Chapter 27 Connectors and APIs

Table of Contents

27.1 MySQL Connector/C++
27.2 MySQL Connector/J
27.3 MySQL Connector/NET
27.4 MySQL Connector/ODBC
27.5 MySQL Connector/Python
27.6 libmysqld, the Embedded MySQL Server Library
27.6.1 Compiling Programs with libmysqld
27.6.2 Restrictions When Using the Embedded MySQL Server
27.6.3 Options with the Embedded Server
27.6.4 Embedded Server Examples
27.7 MySQL C API
27.7.1 MySQL C API Implementations
27.7.2 Example C API Client Programs
27.7.3 Building and Running C API Client Programs
27.7.4 C API Data Structures
27.7.5 C API Function Overview
27.7.6 C API Function Descriptions
27.7.7 C API Prepared Statements
27.7.8 C API Prepared Statement Data Structures
27.7.9 C API Prepared Statement Function Overview
27.7.10 C API Prepared Statement Function Descriptions
27.7.11 C API Threaded Function Descriptions
27.7.12 C API Embedded Server Function Descriptions
27.7.13 C API Client Plugin Functions
27.7.14 C API Encrypted Connection Support
27.7.15 C API Multiple Statement Execution Support
27.7.16 C API Prepared Statement Handling of Date and Time Values
27.7.17 C API Prepared CALL Statement Support
27.7.18 C API Prepared Statement Problems
27.7.19 C API Automatic Reconnection Control
27.7.20 C API Common Issues
27.8 MySQL PHP API
27.9 MySQL Perl API
27.10 MySQL Python API
27.11 MySQL Ruby APIs
27.11.1 The MySQL/Ruby API
27.11.2 The Ruby/MySQL API
27.12 MySQL Tcl API
27.13 MySQL Eiffel Wrapper

MySQL Connectors provide connectivity to the MySQL server for client programs. APIs provide low-level access to the MySQL protocol and MySQL resources. Both Connectors and the APIs enable you to connect and execute MySQL statements from another language or environment, including ODBC, Java (JDBC), Perl, Python, PHP, Ruby, and native C and embedded MySQL instances.

MySQL Connectors

Oracle develops a number of connectors:

The MySQL C API

For direct access to using MySQL natively within a C application, there are two methods:

See also Section 27.7.1, “MySQL C API Implementations”.

To access MySQL from a C application, or to build an interface to MySQL for a language not supported by the Connectors or APIs in this chapter, the C API is where to start. A number of programmer's utilities are available to help with the process; see Section 4.7, “Program Development Utilities”.

Third-Party MySQL APIs

The remaining APIs described in this chapter provide an interface to MySQL from specific application languages. These third-party solutions are not developed or supported by Oracle. Basic information on their usage and abilities is provided here for reference purposes only.

All the third-party language APIs are developed using one of two methods, using libmysqlclient or by implementing a native driver. The two solutions offer different benefits:

Table 27.1, “MySQL APIs and Interfaces” lists many of the libraries and interfaces available for MySQL.

Table 27.1 MySQL APIs and Interfaces

Environment API Type Notes
Ada GNU Ada MySQL Bindings libmysqlclient See MySQL Bindings for GNU Ada
C C API libmysqlclient See Section 27.7, “MySQL C API”.
C++ Connector/C++ libmysqlclient See MySQL Connector/C++ 8.0 Developer Guide.
MySQL++ libmysqlclient See MySQL++ website.
MySQL wrapped libmysqlclient See MySQL wrapped.
Cocoa MySQL-Cocoa libmysqlclient Compatible with the Objective-C Cocoa environment. See http://mysql-cocoa.sourceforge.net/
D MySQL for D libmysqlclient See MySQL for D.
Eiffel Eiffel MySQL libmysqlclient See Section 27.13, “MySQL Eiffel Wrapper”.
Erlang erlang-mysql-driver libmysqlclient See erlang-mysql-driver.
Haskell Haskell MySQL Bindings Native Driver See Brian O'Sullivan's pure Haskell MySQL bindings.
hsql-mysql libmysqlclient See MySQL driver for Haskell.
Java/JDBC Connector/J Native Driver See MySQL Connector/J 5.1 Developer Guide.
Kaya MyDB libmysqlclient See MyDB.
Lua LuaSQL libmysqlclient See LuaSQL.
.NET/Mono Connector/NET Native Driver See MySQL Connector/NET Developer Guide.
Objective Caml OBjective Caml MySQL Bindings libmysqlclient See MySQL Bindings for Objective Caml.
Octave Database bindings for GNU Octave libmysqlclient See Database bindings for GNU Octave.
ODBC Connector/ODBC libmysqlclient See MySQL Connector/ODBC Developer Guide.
Perl DBI/DBD::mysql libmysqlclient See Section 27.9, “MySQL Perl API”.
Net::MySQL Native Driver See Net::MySQL at CPAN
PHP mysql, ext/mysql interface (deprecated) libmysqlclient See Original MySQL API.
mysqli, ext/mysqli interface libmysqlclient See MySQL Improved Extension.
PDO_MYSQL libmysqlclient See MySQL Functions (PDO_MYSQL).
PDO mysqlnd Native Driver
Python Connector/Python Native Driver See MySQL Connector/Python Developer Guide.
Python Connector/Python C Extension libmysqlclient See MySQL Connector/Python Developer Guide.
MySQLdb libmysqlclient See Section 27.10, “MySQL Python API”.
Ruby MySQL/Ruby libmysqlclient Uses libmysqlclient. See Section 27.11.1, “The MySQL/Ruby API”.
Ruby/MySQL Native Driver See Section 27.11.2, “The Ruby/MySQL API”.
Scheme Myscsh libmysqlclient See Myscsh.
SPL sql_mysql libmysqlclient See sql_mysql for SPL.
Tcl MySQLtcl libmysqlclient See Section 27.12, “MySQL Tcl API”.

27.1 MySQL Connector/C++

The MySQL Connector/C++ manual is published in standalone form, not as part of the MySQL Reference Manual. For information, see these documents:

27.2 MySQL Connector/J

The MySQL Connector/J manual is published in standalone form, not as part of the MySQL Reference Manual. For information, see these documents:

27.3 MySQL Connector/NET

The MySQL Connector/NET manual is published in standalone form, not as part of the MySQL Reference Manual. For information, see these documents:

27.4 MySQL Connector/ODBC

The MySQL Connector/ODBC manual is published in standalone form, not as part of the MySQL Reference Manual. For information, see these documents:

27.5 MySQL Connector/Python

The MySQL Connector/Python manual is published in standalone form, not as part of the MySQL Reference Manual. For information, see these documents:

27.6 libmysqld, the Embedded MySQL Server Library

The embedded MySQL server library makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.

Note

The libmysqld embedded server library is deprecated as of MySQL 5.7.19 and will be removed in MySQL 8.0.

The embedded server library is based on the client/server version of MySQL, which is written in C/C++. Consequently, the embedded server also is written in C/C++. There is no embedded server available in other languages.

The API is identical for the embedded MySQL version and the client/server version. To change a threaded application to use the embedded library, you normally only have to add calls to the following functions.

Table 27.2 MySQL Embedded Server Library Functions

Function

When to Call

mysql_library_init()

Call it before any other MySQL function is called, preferably early in the main() function.

mysql_library_end()

Call it before your program exits.

mysql_thread_init()

Call it in each thread you create that accesses MySQL.

mysql_thread_end() Call it before calling pthread_exit().

Then, link your code with libmysqld.a instead of libmysqlclient.a. To ensure binary compatibility between your application and the server library, always compile your application against headers for the same series of MySQL that was used to compile the server library. For example, if libmysqld was compiled against MySQL 5.6 headers, do not compile your application against MySQL 5.7 headers, or vice versa.

Because the mysql_library_xxx() functions are also included in libmysqlclient.a, you can change between the embedded and the client/server version by just linking your application with the right library. See Section 27.7.6.41, “mysql_library_init()”.

One difference between the embedded server and the standalone server is that for the embedded server, authentication for connections is disabled by default.

27.6.1 Compiling Programs with libmysqld

In precompiled binary MySQL distributions that include libmysqld, the embedded server library, MySQL builds the library using the appropriate vendor compiler if there is one.

To get a libmysqld library if you build MySQL from source yourself, you should configure MySQL with the -DWITH_EMBEDDED_SERVER=1 option. See Section 2.9.7, “MySQL Source-Configuration Options”.

When you link your program with libmysqld, you must also include the system-specific pthread libraries and some libraries that the MySQL server uses. You can get the full list of libraries by executing mysql_config --libmysqld-libs.

The correct flags for compiling and linking a threaded program must be used, even if you do not directly call any thread functions in your code.

To compile a C program to include the necessary files to embed the MySQL server library into an executable version of a program, the compiler will need to know where to find various files and need instructions on how to compile the program. The following example shows how a program could be compiled from the command line, assuming that you are using gcc, use the GNU C compiler:

gcc mysql_test.c -o mysql_test \
`/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Immediately following the gcc command is the name of the C program source file. After it, the -o option is given to indicate that the file name that follows is the name that the compiler is to give to the output file, the compiled program. The next line of code tells the compiler to obtain the location of the include files and libraries and other settings for the system on which it is compiled. The mysql_config command is contained in backticks, not single quotation marks.

On some non-gcc platforms, the embedded library depends on C++ runtime libraries and linking against the embedded library might result in missing-symbol errors. To solve this, link using a C++ compiler or explicitly list the required libraries on the link command line.

27.6.2 Restrictions When Using the Embedded MySQL Server

The embedded server has the following limitations:

  • No user-defined functions (UDFs).

  • No stack trace on core dump.

  • You cannot set this up as a master or a slave (no replication).

  • Very large result sets may be unusable on low memory systems.

  • You cannot connect to an embedded server from an outside process with sockets or TCP/IP. However, you can connect to an intermediate application, which in turn can connect to an embedded server on the behalf of a remote client or outside process.

  • libmysqld does not support encrypted connections. An implication is that if an application linked against libmysqld establishes a connection to a remote server, the connection cannot be encrypted.

  • InnoDB is not reentrant in the embedded server and cannot be used for multiple connections, either successively or simultaneously.

  • The Event Scheduler is not available. Because of this, the event_scheduler system variable is disabled.

  • The Performance Schema is not available.

  • The embedded server cannot share the same secure_file_priv directory with another server. As of MySQL 5.7.8, the default value for this directory can be set at build time with the INSTALL_SECURE_FILE_PRIV_EMBEDDEDDIR CMake option.

Some of these limitations can be changed by editing the mysql_embed.h include file and recompiling MySQL.

27.6.3 Options with the Embedded Server

Any options that may be given with the mysqld server daemon, may be used with an embedded server library. Server options may be given in an array as an argument to the mysql_library_init(), which initializes the server. They also may be given in an option file like my.cnf. To specify an option file for a C program, use the --defaults-file option as one of the elements of the second argument of the mysql_library_init() function. See Section 27.7.6.41, “mysql_library_init()”, for more information on the mysql_library_init() function.

Using option files can make it easier to switch between a client/server application and one where MySQL is embedded. Put common options under the [server] group. These are read by both MySQL versions. Client/server-specific options should go under the [mysqld] section. Put options specific to the embedded MySQL server library in the [embedded] section. Options specific to applications go under section labeled [ApplicationName_SERVER]. See Section 4.2.2.2, “Using Option Files”.

27.6.4 Embedded Server Examples

These two example programs should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes are needed, mostly with file paths. These examples are designed to give enough details for you to understand the problem, without the clutter that is a necessary part of a real application. The first example is very straightforward. The second example is a little more advanced with some error checking. The first is followed by a command-line entry for compiling the program. The second is followed by a GNUmake file that may be used for compiling instead.

Example 1

test1_libmysqld.c

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include "mysql.h"

MYSQL *mysql;
MYSQL_RES *results;
MYSQL_ROW record;

static char *server_options[] = \
       { "mysql_test", "--defaults-file=my.cnf", NULL };
int num_elements = (sizeof(server_options) / sizeof(char *)) - 1;

static char *server_groups[] = { "libmysqld_server",
                                 "libmysqld_client", NULL };

int main(void)
{
   mysql_library_init(num_elements, server_options, server_groups);
   mysql = mysql_init(NULL);
   mysql_options(mysql, MYSQL_READ_DEFAULT_GROUP, "libmysqld_client");
   mysql_options(mysql, MYSQL_OPT_USE_EMBEDDED_CONNECTION, NULL);

   mysql_real_connect(mysql, NULL,NULL,NULL, "database1", 0,NULL,0);

   mysql_query(mysql, "SELECT column1, column2 FROM table1");

   results = mysql_store_result(mysql);

   while((record = mysql_fetch_row(results))) {
      printf("%s - %s \n", record[0], record[1]);
   }

   mysql_free_result(results);
   mysql_close(mysql);
   mysql_library_end();

   return 0;
}

Here is the command line for compiling the above program:

gcc test1_libmysqld.c -o test1_libmysqld \
 `/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Example 2

To try the example, create an test2_libmysqld directory at the same level as the MySQL source directory. Save the test2_libmysqld.c source and the GNUmakefile in the directory, and run GNU make from inside the test2_libmysqld directory.

test2_libmysqld.c

/*
 * A simple example client, using the embedded MySQL server library
*/

#include <mysql.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

MYSQL *db_connect(const char *dbname);
void db_disconnect(MYSQL *db);
void db_do_query(MYSQL *db, const char *query);

const char *server_groups[] = {
  "test2_libmysqld_SERVER", "embedded", "server", NULL
};

int
main(int argc, char **argv)
{
  MYSQL *one, *two;

  /* mysql_library_init() must be called before any other mysql
   * functions.
   *
   * You can use mysql_library_init(0, NULL, NULL), and it
   * initializes the server using groups = {
   *   "server", "embedded", NULL
   *  }.
   *
   * In your $HOME/.my.cnf file, you probably want to put:

[test2_libmysqld_SERVER]
language = /path/to/source/of/mysql/sql/share/english

   * You could, of course, modify argc and argv before passing
   * them to this function.  Or you could create new ones in any
   * way you like.  But all of the arguments in argv (except for
   * argv[0], which is the program name) should be valid options
   * for the MySQL server.
   *
   * If you link this client against the normal mysqlclient
   * library, this function is just a stub that does nothing.
   */
  mysql_library_init(argc, argv, (char **)server_groups);

  one = db_connect("test");
  two = db_connect(NULL);

  db_do_query(one, "SHOW TABLE STATUS");
  db_do_query(two, "SHOW DATABASES");

  mysql_close(two);
  mysql_close(one);

  /* This must be called after all other mysql functions */
  mysql_library_end();

  exit(EXIT_SUCCESS);
}

static void
die(MYSQL *db, char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  (void)putc('\n', stderr);
  if (db)
    db_disconnect(db);
  exit(EXIT_FAILURE);
}

MYSQL *
db_connect(const char *dbname)
{
  MYSQL *db = mysql_init(NULL);
  if (!db)
    die(db, "mysql_init failed: no memory");
  /*
   * Notice that the client and server use separate group names.
   * This is critical, because the server does not accept the
   * client's options, and vice versa.
   */
  mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test2_libmysqld_CLIENT");
  if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0))
    die(db, "mysql_real_connect failed: %s", mysql_error(db));

  return db;
}

void
db_disconnect(MYSQL *db)
{
  mysql_close(db);
}

void
db_do_query(MYSQL *db, const char *query)
{
  if (mysql_query(db, query) != 0)
    goto err;

  if (mysql_field_count(db) > 0)
  {
    MYSQL_RES   *res;
    MYSQL_ROW    row, end_row;
    int num_fields;

    if (!(res = mysql_store_result(db)))
      goto err;
    num_fields = mysql_num_fields(res);
    while ((row = mysql_fetch_row(res)))
    {
      (void)fputs(">> ", stdout);
      for (end_row = row + num_fields; row < end_row; ++row)
        (void)printf("%s\t", row ? (char*)*row : "NULL");
      (void)fputc('\n', stdout);
    }
    (void)fputc('\n', stdout);
    mysql_free_result(res);
  }
  else
    (void)printf("Affected rows: %lld\n", mysql_affected_rows(db));

  return;

err:
  die(db, "db_do_query failed: %s [%s]", mysql_error(db), query);
}

GNUmakefile

# This assumes the MySQL software is installed in /usr/local/mysql
inc      := /usr/local/mysql/include/mysql
lib      := /usr/local/mysql/lib

# If you have not installed the MySQL software yet, try this instead
#inc      := $(HOME)/mysql-5.7/include
#lib      := $(HOME)/mysql-5.7/libmysqld

CC       := gcc
CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT
CFLAGS   := -g -W -Wall
LDFLAGS  := -static
# You can change -lmysqld to -lmysqlclient to use the
# client/server library
LDLIBS    = -L$(lib) -lmysqld -lm -ldl -lcrypt

ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null))
# FreeBSD
LDFLAGS += -pthread
else
# Assume Linux
LDLIBS += -lpthread
endif

# This works for simple one-file test programs
sources := $(wildcard *.c)
objects := $(patsubst %c,%o,$(sources))
targets := $(basename $(sources))

all: $(targets)

clean:
rm -f $(targets) $(objects) *.core

27.7 MySQL C API

The C API provides low-level access to the MySQL client/server protocol and enables C programs to access database contents. The C API code is distributed with MySQL and implemented in the libmysqlclient library. See Section 27.7.1, “MySQL C API Implementations”.

Most other client APIs use the libmysqlclient library to communicate with the MySQL server. (Exceptions are Connector/J and Connector/NET.) This means that, for example, you can take advantage of many of the same environment variables that are used by other client programs because they are referenced from the library. For a list of these variables, see Section 4.1, “Overview of MySQL Programs”.

For instructions on building client programs using the C API, see Section 27.7.3.1, “Building C API Client Programs”. For programming with threads, see Section 27.7.3.3, “Writing C API Threaded Client Programs”. To create a standalone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see Section 27.6, “libmysqld, the Embedded MySQL Server Library”.

Note

If, after an upgrade, you experience problems with compiled client programs, such as Commands out of sync or unexpected core dumps, the programs were probably compiled using old header or library files. In this case, check the date of the mysql.h file and libmysqlclient.a library used for compilation to verify that they are from the new MySQL distribution. If not, recompile the programs with the new headers and libraries. Recompilation might also be necessary for programs compiled against the shared client library if the library major version number has changed (for example, from libmysqlclient.so.17 to libmysqlclient.so.18). For additional compatibility information, see Section 27.7.3.4, “Running C API Client Programs”.

Clients have a maximum communication buffer size. The size of the buffer that is allocated initially (16KB) is automatically increased up to the maximum size (16MB by default). Because buffer sizes are increased only as demand warrants, simply increasing the maximum limit does not in itself cause more resources to be used. This size check is mostly a precaution against erroneous statements and communication packets.

The communication buffer must be large enough to contain a single SQL statement (for client-to-server traffic) and one row of returned data (for server-to-client traffic). Each session's communication buffer is dynamically enlarged to handle any query or row up to the maximum limit. For example, if you have BLOB values that contain up to 16MB of data, you must have a communication buffer limit of at least 16MB (in both server and client). The default maximum built into the client library is 1GB, but the default maximum in the server is 1MB. You can increase this by changing the value of the max_allowed_packet parameter at server startup. See Section 5.1.1, “Configuring the Server”.

The MySQL server shrinks each communication buffer to net_buffer_length bytes after each query. For clients, the size of the buffer associated with a connection is not decreased until the connection is closed, at which time client memory is reclaimed.

27.7.1 MySQL C API Implementations

The MySQL C API is a C-based API that client applications written in C can use to communicate with MySQL Server. Client programs refer to C API header files at compile time and link to a C API library file at link time. The library comes in two versions, depending on how the application is intended to communicate with the server:

  • libmysqlclient: The client version of the library, used for applications that communicate over a network connection as a client of a standalone server process.

  • libmysqld: The embedded server version of the library, used for applications intended to include an embedded MySQL server within the application itself. The application communicates with its own private server instance.

    Note

    The libmysqld embedded server library is deprecated as of MySQL 5.7.19 and will be removed in MySQL 8.0.

Both libraries have the same interface. In terms of C API calls, an application communicates with a standalone server the same way it communicates with an embedded server. A given client can be built to communicate with a standalone or embedded server, depending on whether it is linked against libmysqlclient or libmysqld at build time.

To obtain the C API header and library files required to build C API client programs, install a MySQL Server distribution. Server distributions include both libmysqlclient and libmysqld.

You can install a binary distribution that contains the C API files pre-built, or you can use a source distribution and build the C API files yourself.

The names of the library files to use when linking C API client applications depend on the library type and platform for which a distribution is built:

  • On Unix (and Unix-like) systems, the static library is libmysqlclient.a. The dynamic library is libmysqlclient.so on most Unix systems and libmysqlclient.dylib on macOS.

    For distributions that include embedded server libraries, the corresponding library names begin with libmysqld rather than libmysqlclient.

  • On Windows, the static library is mysqlclient.lib and the dynamic library is libmysql.dll. Windows distributions also include libmysql.lib, a static import library needed for using the dynamic library.

    For distributions that include embedded server libraries, the corresponding library names are mysqlserver.lib, libmysqld.dll, and libmysqld.lib.

    Windows distributions also include a set of debug libraries. These have the same names as the nondebug libraries, but are located in the lib/debug library. You must use the debug libraries when compiling clients built using the debug C runtime.

On Unix, you may also see libraries that include _r in the names. Before MySQL 5.5, these were built as thread-safe (re-entrant) libraries separately from the non-_r libraries. As of 5.5, both libraries are the same and the _r names are symbolic links to the corresponding non-_r names. There is no need to use the _r libraries. For example, if you use mysql_config to obtain linker flags, you can use mysql_config --libs in all cases, even for threaded clients. There is no need to use mysql_config --libs_r.

27.7.2 Example C API Client Programs

Many of the clients in MySQL source distributions are written in C, such as mysql, mysqladmin, and mysqlshow. If you are looking for examples that demonstrate how to use the C API, take a look at those clients: Obtain a source distribution and look in its client directory. See Section 2.1.2, “How to Get MySQL”.

For information about individual C API functions, the sections for most functions include usage examples.

27.7.3 Building and Running C API Client Programs

The following sections provide information on building client programs that use the C API. Topics include compiling and linking clients, writing threaded clients, and troubleshooting runtime problems.

27.7.3.1 Building C API Client Programs

This section provides guidelines for compiling C programs that use the MySQL C API.

Compiling MySQL Clients on Unix

The examples here use gcc as the compiler. A different compiler might be appropriate on some systems (for example, clang on macOS or FreeBSD, or Sun Studio on Solaris). Adjust the examples as necessary.

You may need to specify an -I option when you compile client programs that use MySQL header files, so that the compiler can find them. For example, if the header files are installed in /usr/local/mysql/include, use this option in the compile command:

-I/usr/local/mysql/include

You can link your code with either the dynamic or static MySQL C client library. The dynamic library base name is libmysqlclient and the suffix differs by platform (for example, .so for Linux, .dylib for macOS). The static library is named libmysqlclient.a on all platforms.

MySQL clients must be linked using the -lmysqlclient option in the link command. You may also need to specify a -L option to tell the linker where to find the library. For example, if the library is installed in /usr/local/mysql/lib, use these options in the link command:

-L/usr/local/mysql/lib -lmysqlclient

The path names may differ on your system. Adjust the -I and -L options as necessary.

To make it simpler to compile MySQL programs on Unix, use the mysql_config script. See Section 4.7.1, “mysql_config — Display Options for Compiling Clients”.

mysql_config displays the options needed for compiling or linking:

mysql_config --cflags
mysql_config --libs

You can invoke those commands at the command line to get the proper options and add them manually to compilation or link commands. Alternatively, include the output from mysql_config directly within command lines using backticks:

gcc -c `mysql_config --cflags` progname.c
gcc -o progname progname.o `mysql_config --libs`

On Unix, linking uses dynamic libraries by default. To link to the static client library instead, add its path name to the link command. For example, if the library is located in /usr/local/mysql/lib, link like this:

gcc -o progname progname.o /usr/local/mysql/lib/libmysqlclient.a

Or use mysql_config to provide the path to the library:

gcc -o progname progname.o `mysql_config --variable=pkglibdir`/libmysqlclient.a

mysql_config does not currently provide a way to list all libraries needed for static linking, so it might be necessary to name additional libraries on the link command (for example, -lnsl -lsocket on Solaris). To get an idea which libraries to add, use mysql_config --libs and ldd libmysqlclient.so (or otool -L libmysqlclient.dylib on macOS).

pkg-config can be used as an alternative to mysql_config for obtaining information such as compiler flags or link libraries required to compile MySQL applications. For example, the following pairs of commands are equivalent:

mysql_config --cflags
pkg-config --cflags mysqlclient

mysql_config --libs
pkg-config --libs mysqlclient

To produce flags for static linking, use this command:

pkg-config --static --libs mysqlclient

For more information, see Section 27.7.3.2, “Building C API Client Programs Using pkg-config”.

Compiling MySQL Clients on Microsoft Windows

To specify header and library file locations, use the facilities provided by your development environment.

To build C API clients on Windows, you must link in the C client library, as well as the Windows ws2_32 sockets library and Secur32 security library.

You can link your code with either the dynamic or static MySQL C client library:

  • The dynamic library is named libmysql.dll. In addition, the libmysql.lib static import library is needed for using the dynamic library.

  • The static library is named mysqlclient.lib. To link with the static C client library, the client application must be compiled with the same version of Visual Studio used to compile the C client library (which is Visual Studio 2013 for the static C client library built by Oracle).

When using the Oracle-built MySQL C client library, follow these rules when it comes to linking the C runtime for your client application:

  • For the MySQL C client library from a Community distribution of MySQL:

    • For MySQL 5.7.18 and higher: Always link dynamically to the C runtime (use the /MD compiler option), whether you are linking to the static or dynamic C client library. Also, target hosts running the client application must have the Visual C++ Redistributable for Visual Studio 2013 installed.

    • For MySQL 5.7.17 and lower:

      • If linking to the static C client library, link statically to the C runtime (use the /MT compiler option).

      • If linking to the dynamic C client library, link either statically or dynamically to the C runtime (use either /MT or /MD compiler option).

  • For the MySQL C client library from a Commercial distribution of MySQL:

    • If linking to the static C client library, link statically to the C runtime (use the /MT compiler option).

    • If linking to the dynamic C client library, link either statically or dynamically to the C runtime (use either /MT or /MD compiler option).

In general, when linking to a static MySQL C client library, the client library and the client application must use the same compiler options when it comes to linking the C runtime—that is, if your C client library is compiled with the /MT option, your client application should also be compiled with the /MT option, and so on (see the MSDN page describing the C library linking options for more details). Follow this rule when you build your own static MySQL C client library from a source distribution of MySQL and link your client application to it.

Note

Debug Mode: Because of the just-mentioned linking rule, you cannot build your application in debug mode (with the /MTd or /MDd compiler option) and link it to a static C client library built by Oracle, which is not built with the debug options. Instead, you must build the static client library from source with the debug options.

Troubleshooting Problems Linking to the MySQL Client Library

The MySQL client library includes SSL support built in. It is unnecessary to specify either -lssl or -lcrypto at link time. Doing so may in fact result in problems at runtime.

If the linker cannot find the MySQL client library, you might get undefined-reference errors for symbols that start with mysql_, such as those shown here:

/tmp/ccFKsdPa.o: In function `main':
/tmp/ccFKsdPa.o(.text+0xb): undefined reference to `mysql_init'
/tmp/ccFKsdPa.o(.text+0x31): undefined reference to `mysql_real_connect'
/tmp/ccFKsdPa.o(.text+0x69): undefined reference to `mysql_error'
/tmp/ccFKsdPa.o(.text+0x9a): undefined reference to `mysql_close'

You should be able to solve this problem by adding -Ldir_path -lmysqlclient at the end of your link command, where dir_path represents the path name of the directory where the client library is located. To determine the correct directory, try this command:

mysql_config --libs

The output from mysql_config might indicate other libraries that should be specified on the link command as well. You can include mysql_config output directly in your compile or link command using backticks. For example:

gcc -o progname progname.o `mysql_config --libs`

If an error occurs at link time that the floor symbol is undefined, link to the math library by adding -lm to the end of the compile/link line. Similarly, if you get undefined-reference errors for other functions that should exist on your system, such as connect(), check the manual page for the function in question to determine which libraries you should add to the link command.

If you get undefined-reference errors such as the following for functions that do not exist on your system, it usually means that your MySQL client library was compiled on a system that is not 100% compatible with yours:

mf_format.o(.text+0x201): undefined reference to `__lxstat'

In this case, you should download a source distribution for the latest version of MySQL and compile the MySQL client library yourself. See Section 2.9, “Installing MySQL from Source”.

27.7.3.2 Building C API Client Programs Using pkg-config

MySQL distributions contain a mysqlclient.pc file that provides information about MySQL configuration for use by the pkg-config command. This enables pkg-config to be used as an alternative to mysql_config for obtaining information such as compiler flags or link libraries required to compile MySQL applications. For example, the following pairs of commands are equivalent:

mysql_config --cflags
pkg-config --cflags mysqlclient

mysql_config --libs
pkg-config --libs mysqlclient

The last pkg-config command produces flags for dynamic linking. To produce flags for static linking, use this command:

pkg-config --static --libs mysqlclient

On some platforms, the output with and without --static might be the same.

Note

If pkg-config does not find MySQL information, it might be necessary to set the PKG_CONFIG_PATH environment variable to the directory in which the mysqlclient.pc file is located, which by default is usually the pkgconfig directory under the MySQL library directory. For example (adjust the location appropriately):

# For sh, bash, ...
export PKG_CONFIG_PATH=/usr/local/mysql/lib/pkgconfig
# For csh, tcsh, ...
setenv PKG_CONFIG_PATH /usr/local/mysql/lib/pkgconfig

The mysqlconfig.pc installation location can be controlled using the INSTALL_PKGCONFIGDIR CMake option. See Section 2.9.7, “MySQL Source-Configuration Options”.

The --variable option takes a configuration variable name and displays the variable value:

# installation prefix directory
pkg-config --variable=prefix mysqlclient
# header file directory
pkg-config --variable=includedir mysqlclient
# library directory
pkg-config --variable=libdir mysqlclient

To see which variable values pkg-config can display using the --variable option, use this command:

pkg-config --print-variables mysqlclient

You can use pkg-config within a command line using backticks to include the output that it produces for particular options. For example, to compile and link a MySQL client program, use pkg-config as follows:

gcc -c `pkg-config --cflags mysqlclient` progname.c
gcc -o progname progname.o `pkg-config --libs mysqlclient`

27.7.3.3 Writing C API Threaded Client Programs

This section provides guidance for writing client programs that use the thread-related functions in the MySQL C API. For further information about these functions, see Section 27.7.11, “C API Threaded Function Descriptions”. For examples of source code that uses them, look in the client directory of a MySQL source distribution:

  • The source for mysqlimport uses threading in the code associated with the --use-threads option.

  • The source for mysqlslap uses threads to set up simultaneous workloads, to test server operation under high load.

If undefined-reference errors occur when linking a threaded program against the MySQL client library, the most likely cause is that you did not include the thread libraries on the link/compile command.

The client library is almost thread-safe. The biggest problem is that the subroutines in sql/net_serv.cc that read from sockets are not interrupt-safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. If you install interrupt handlers for the SIGPIPE interrupt, socket handling should be thread-safe.

To avoid aborting the program when a connection terminates, MySQL blocks SIGPIPE on the first call to mysql_library_init(), mysql_init(), or mysql_connect(). To use your own SIGPIPE handler, first call mysql_library_init(), then install your handler.

The client library is thread-safe per connection. Two threads can share the same connection with the following caveats:

  • Multiple threads cannot send a query to the MySQL server at the same time on the same connection. In particular, you must ensure that between calls to mysql_query() and mysql_store_result() in one thread, no other thread uses the same connection. To do this, use a mutex lock around your pair of mysql_query() and mysql_store_result() calls. After mysql_store_result() returns, the lock can be released and other threads may query the same connection.

    If you use POSIX threads, you can use pthread_mutex_lock() and pthread_mutex_unlock() to establish and release a mutex lock.

    Note

    If you examine programs in a MySQL source distribution, instead of calls to pthread_mutex_lock() and pthread_mutex_unlock(), you will see calls to native_mutex_lock() and native_mutex_unlock(). The latter functions are defined in the thr_mutex.h header file and map to platform-specific mutex functions.

  • Multiple threads can access different result sets that are retrieved with mysql_store_result().

  • To use mysql_use_result(), you must ensure that no other thread uses the same connection until the result set is closed. However, it really is best for threaded clients that share the same connection to use mysql_store_result().

If a thread does not create the connection to the MySQL database but calls MySQL functions, take the following into account:

When you call mysql_init(), MySQL creates a thread-specific variable for the thread that is used by the debug library (among other things). If you call a MySQL function before the thread has called mysql_init(), the thread does not have the necessary thread-specific variables in place and you are likely to end up with a core dump sooner or later. To avoid problems, you must do the following:

  1. Call mysql_library_init() before any other MySQL functions. It is not thread-safe, so call it before threads are created, or protect the call with a mutex.

  2. Arrange for mysql_thread_init() to be called early in the thread handler before calling any MySQL function. (If you call mysql_init(), it calls mysql_thread_init() for you.)

  3. In the thread, call mysql_thread_end() before calling pthread_exit(). This frees the memory used by MySQL thread-specific variables.

The preceding notes regarding mysql_init() also apply to mysql_connect(), which calls mysql_init().

27.7.3.4 Running C API Client Programs

If, after an upgrade, you experience problems with compiled client programs, such as Commands out of sync or unexpected core dumps, the programs were probably compiled using old header or library files. In this case, check the date of the mysql.h header file and libmysqlclient.a library used for compilation to verify that they are from the new MySQL distribution. If not, recompile the programs with the new headers and libraries. Recompilation might also be necessary for programs compiled against the shared client library if the library major version number has changed (for example, from libmysqlclient.so.17 to libmysqlclient.so.18).

The major shared client library version determines compatibility. (For example, for libmysqlclient.so.18.1.0, the major version is 18.) Libraries shipped with newer versions of MySQL are drop-in replacements for older versions that have the same major number. As long as the major library version is the same, you can upgrade the library and old applications should continue to work with it.

Undefined-reference errors might occur at runtime when you try to execute a MySQL program. If these errors specify symbols that start with mysql_ or indicate that the libmysqlclient library cannot be found, it means that your system cannot find the shared libmysqlclient.so library. The solution to this problem is to tell your system to search for shared libraries in the directory where that library is located. Use whichever of the following methods is appropriate for your system:

  • Add the path of the directory where libmysqlclient.so is located to the LD_LIBRARY_PATH or LD_LIBRARY environment variable.

  • On macOS, add the path of the directory where libmysqlclient.dylib is located to the DYLD_LIBRARY_PATH environment variable.

  • Copy the shared-library files (such as libmysqlclient.so) to some directory that is searched by your system, such as /lib, and update the shared library information by executing ldconfig. Be sure to copy all related files. A shared library might exist under several names, using symlinks to provide the alternate names.

If the application is linked to the embedded server library, runtime error messages indicate the libmysqld rather than libmysqlclient library, but the solution to the problem is the same as just described.

27.7.3.5 C API Server Version and Client Library Version

The string and numeric forms of the MySQL server version are available at compile time as the values of the MYSQL_SERVER_VERSION and MYSQL_VERSION_ID macros, and at runtime as the values of the mysql_get_server_info() and mysql_get_server_version() functions.

The client library version is the MySQL version. The string and numeric forms of this version are available at compile time as the values of the MYSQL_SERVER_VERSION and MYSQL_VERSION_ID macros, and at runtime as the values of the mysql_get_client_info() and mysql_get_client_version() functions.

27.7.4 C API Data Structures

This section describes C API data structures other than those used for prepared statements. For information about the latter, see Section 27.7.8, “C API Prepared Statement Data Structures”.

  • MYSQL

    This structure represents handler for one database connection. It is used for almost all MySQL functions. Do not try to make a copy of a MYSQL structure. There is no guarantee that such a copy will be usable.

  • MYSQL_RES

    This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section.

  • MYSQL_ROW

    This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row().

  • MYSQL_FIELD

    This structure contains metadata: information about a field, such as the field's name, type, and size. Its members are described in more detail later in this section. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure.

  • MYSQL_FIELD_OFFSET

    This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.

  • my_ulonglong

    The type used for the number of rows and for mysql_affected_rows(), mysql_num_rows(), and mysql_insert_id(). This type provides a range of 0 to 1.84e19.

    Some functions that return a row count using this type return -1 as an unsigned value to indicate an error or exceptional condition. You can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

    On some systems, attempting to print a value of type my_ulonglong does not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:

    printf ("Number of rows: %lu\n",
            (unsigned long) mysql_num_rows(result));
  • my_bool

    A boolean type, for values that are true (nonzero) or false (zero).

The MYSQL_FIELD structure contains the members described in the following list. The definitions apply primarily for columns of result sets such as those produced by SELECT statements. MYSQL_FIELD structures are also used to provide metadata for OUT and INOUT parameters returned from stored procedures executed using prepared CALL statements. For such parameters, some of the structure members have a meaning different from the meaning for column values.

  • char * name

    The name of the field, as a null-terminated string. If the field was given an alias with an AS clause, the value of name is the alias. For a procedure parameter, the parameter name.

  • char * org_name

    The name of the field, as a null-terminated string. Aliases are ignored. For expressions, the value is an empty string. For a procedure parameter, the parameter name.

  • char * table

    The name of the table containing this field, if it is not a calculated field. For calculated fields, the table value is an empty string. If the column is selected from a view, table names the view. If the table or view was given an alias with an AS clause, the value of table is the alias. For a UNION, the value is the empty string. For a procedure parameter, the procedure name.

  • char * org_table

    The name of the table, as a null-terminated string. Aliases are ignored. If the column is selected from a view, org_table names the view. If the column is selected from a derived table, org_table names the base table. If a derived table wraps a view, org_table still names the base table. If the column is an expression, org_table is the empty string. For a UNION, the value is the empty string. For a procedure parameter, the value is the procedure name.

  • char * db

    The name of the database that the field comes from, as a null-terminated string. If the field is a calculated field, db is an empty string. For a UNION, the value is the empty string. For a procedure parameter, the name of the database containing the procedure.

  • char * catalog

    The catalog name. This value is always "def".

  • char * def

    The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields().

  • unsigned long length

    The width of the field. This corresponds to the display length, in bytes.

    The server determines the length value before it generates the result set, so this is the minimum length required for a data type capable of holding the largest possible value from the result column, without knowing in advance the actual values that will be produced by the query for the result set.

  • unsigned long max_length

    The maximum width of the field for the result set (the length in bytes of the longest field value for the rows actually in the result set). If you use mysql_store_result() or mysql_list_fields(), this contains the maximum length for the field. If you use mysql_use_result(), the value of this variable is zero.

    The value of max_length is the length of the string representation of the values in the result set. For example, if you retrieve a FLOAT column and the widest value is -12.345, max_length is 7 (the length of '-12.345').

    If you are using prepared statements, max_length is not set by default because for the binary protocol the lengths of the values depend on the types of the values in the result set. (See Section 27.7.8, “C API Prepared Statement Data Structures”.) If you want the max_length values anyway, enable the STMT_ATTR_UPDATE_MAX_LENGTH option with mysql_stmt_attr_set() and the lengths will be set when you call mysql_stmt_store_result(). (See Section 27.7.10.3, “mysql_stmt_attr_set()”, and Section 27.7.10.28, “mysql_stmt_store_result()”.)

  • unsigned int name_length

    The length of name.

  • unsigned int org_name_length

    The length of org_name.

  • unsigned int table_length

    The length of table.

  • unsigned int org_table_length

    The length of org_table.

  • unsigned int db_length

    The length of db.

  • unsigned int catalog_length

    The length of catalog.

  • unsigned int def_length

    The length of def.

  • unsigned int flags

    Bit-flags that describe the field. The flags value may have zero or more of the bits set that are shown in the following table.

    Flag Value Flag Description
    NOT_NULL_FLAG Field cannot be NULL
    PRI_KEY_FLAG Field is part of a primary key
    UNIQUE_KEY_FLAG Field is part of a unique key
    MULTIPLE_KEY_FLAG Field is part of a nonunique key
    UNSIGNED_FLAG Field has the UNSIGNED attribute
    ZEROFILL_FLAG Field has the ZEROFILL attribute
    BINARY_FLAG Field has the BINARY attribute
    AUTO_INCREMENT_FLAG Field has the AUTO_INCREMENT attribute
    ENUM_FLAG Field is an ENUM
    SET_FLAG Field is a SET
    BLOB_FLAG Field is a BLOB or TEXT (deprecated)
    TIMESTAMP_FLAG Field is a TIMESTAMP (deprecated)
    NUM_FLAG Field is numeric; see additional notes following table
    NO_DEFAULT_VALUE_FLAG Field has no default value; see additional notes following table

    Some of these flags indicate data type information and are superseded by or used in conjunction with the MYSQL_TYPE_xxx value in the field->type member described later:

    • To check for BLOB or TIMESTAMP values, check whether type is MYSQL_TYPE_BLOB or MYSQL_TYPE_TIMESTAMP. (The BLOB_FLAG and TIMESTAMP_FLAG flags are unneeded.)

    • ENUM and SET values are returned as strings. For these, check that the type value is MYSQL_TYPE_STRING and that the ENUM_FLAG or SET_FLAG flag is set in the flags value.

    NUM_FLAG indicates that a column is numeric. This includes columns with a type of MYSQL_TYPE_DECIMAL, MYSQL_TYPE_NEWDECIMAL, MYSQL_TYPE_TINY, MYSQL_TYPE_SHORT, MYSQL_TYPE_LONG, MYSQL_TYPE_FLOAT, MYSQL_TYPE_DOUBLE, MYSQL_TYPE_NULL, MYSQL_TYPE_LONGLONG, MYSQL_TYPE_INT24, and MYSQL_TYPE_YEAR.

    NO_DEFAULT_VALUE_FLAG indicates that a column has no DEFAULT clause in its definition. This does not apply to NULL columns (because such columns have a default of NULL), or to AUTO_INCREMENT columns (which have an implied default value).

    The following example illustrates a typical use of the flags value:

    if (field->flags & NOT_NULL_FLAG)
        printf("Field cannot be null\n");

    You may use the convenience macros shown in the following table to determine the boolean status of the flags value.

    Flag Status Description
    IS_NOT_NULL(flags) True if this field is defined as NOT NULL
    IS_PRI_KEY(flags) True if this field is a primary key
    IS_BLOB(flags) True if this field is a BLOB or TEXT (deprecated; test field->type instead)
  • unsigned int decimals

    The number of decimals for numeric fields, and the fractional seconds precision for temporal fields.

  • unsigned int charsetnr

    An ID number that indicates the character set/collation pair for the field.

    Normally, character values in result sets are converted to the character set indicated by the character_set_results system variable. In this case, charsetnr corresponds to the character set indicated by that variable. Character set conversion can be suppressed by setting character_set_results to NULL. In this case, charsetnr corresponds to the character set of the original table column or expression. See also Section 10.4, “Connection Character Sets and Collations”.

    To distinguish between binary and nonbinary data for string data types, check whether the charsetnr value is 63. If so, the character set is binary, which indicates binary rather than nonbinary data. This enables you to distinguish BINARY from CHAR, VARBINARY from VARCHAR, and the BLOB types from the TEXT types.

    charsetnr values are the same as those displayed in the Id column of the SHOW COLLATION statement or the ID column of the INFORMATION_SCHEMA COLLATIONS table. You can use those information sources to see which character set and collation specific charsetnr values indicate:

    mysql> SHOW COLLATION WHERE Id = 63;
    +-----------+---------+----+---------+----------+---------+
    | Collation | Charset | Id | Default | Compiled | Sortlen |
    +-----------+---------+----+---------+----------+---------+
    | binary    | binary  | 63 | Yes     | Yes      |       1 |
    +-----------+---------+----+---------+----------+---------+
    
    mysql> SELECT COLLATION_NAME, CHARACTER_SET_NAME
           FROM INFORMATION_SCHEMA.COLLATIONS WHERE ID = 33;
    +-----------------+--------------------+
    | COLLATION_NAME  | CHARACTER_SET_NAME |
    +-----------------+--------------------+
    | utf8_general_ci | utf8               |
    +-----------------+--------------------+
    
  • enum enum_field_types type

    The type of the field. The type value may be one of the MYSQL_TYPE_ symbols shown in the following table.

    Type Value Type Description
    MYSQL_TYPE_TINY TINYINT field
    MYSQL_TYPE_SHORT SMALLINT field
    MYSQL_TYPE_LONG INTEGER field
    MYSQL_TYPE_INT24 MEDIUMINT field
    MYSQL_TYPE_LONGLONG BIGINT field
    MYSQL_TYPE_DECIMAL DECIMAL or NUMERIC field
    MYSQL_TYPE_NEWDECIMAL Precision math DECIMAL or NUMERIC
    MYSQL_TYPE_FLOAT FLOAT field
    MYSQL_TYPE_DOUBLE DOUBLE or REAL field
    MYSQL_TYPE_BIT BIT field
    MYSQL_TYPE_TIMESTAMP TIMESTAMP field
    MYSQL_TYPE_DATE DATE field
    MYSQL_TYPE_TIME TIME field
    MYSQL_TYPE_DATETIME DATETIME field
    MYSQL_TYPE_YEAR YEAR field
    MYSQL_TYPE_STRING CHAR or BINARY field
    MYSQL_TYPE_VAR_STRING VARCHAR or VARBINARY field
    MYSQL_TYPE_BLOB BLOB or TEXT field (use max_length to determine the maximum length)
    MYSQL_TYPE_SET SET field
    MYSQL_TYPE_ENUM ENUM field
    MYSQL_TYPE_GEOMETRY Spatial field
    MYSQL_TYPE_NULL NULL-type field

    The MYSQL_TYPE_TIME2, MYSQL_TYPE_DATETIME2, and MYSQL_TYPE_TIMESTAMP2) type codes are used only on the server side. Clients see the MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, and MYSQL_TYPE_TIMESTAMP codes.

    You can use the IS_NUM() macro to test whether a field has a numeric type. Pass the type value to IS_NUM() and it evaluates to TRUE if the field is numeric:

    if (IS_NUM(field->type))
        printf("Field is numeric\n");

    ENUM and SET values are returned as strings. For these, check that the type value is MYSQL_TYPE_STRING and that the ENUM_FLAG or SET_FLAG flag is set in the flags value.

27.7.5 C API Function Overview

The following list summarizes the functions available in the C API. For greater detail, see the descriptions in Section 27.7.6, “C API Function Descriptions”.

Application programs should use this general outline for interacting with MySQL:

  1. Initialize the MySQL client library by calling mysql_library_init(). This function exists in both the libmysqlclient C client library and the libmysqld embedded server library, so it is used whether you build a regular client program by linking with the -libmysqlclient flag, or an embedded server application by linking with the -libmysqld flag.

  2. Initialize a connection handler by calling mysql_init() and connect to the server by calling mysql_real_connect().

  3. Issue SQL statements and process their results. (The following discussion provides more information about how to do this.)

  4. Close the connection to the MySQL server by calling mysql_close().

  5. End use of the MySQL client library by calling mysql_library_end().

The purpose of calling mysql_library_init() and mysql_library_end() is to provide proper initialization and finalization of the MySQL client library. For applications that are linked with the client library, they provide improved memory management. If you do not call mysql_library_end(), a block of memory remains allocated. (This does not increase the amount of memory used by the application, but some memory leak detectors will complain about it.) For applications that are linked with the embedded server, these calls start and stop the server.

In a nonmultithreaded environment, the call to mysql_library_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, mysql_library_init() is not thread-safe in a multithreaded environment, and thus neither is mysql_init(), which calls mysql_library_init(). You must either call mysql_library_init() prior to spawning any threads, or else use a mutex to protect the call, whether you invoke mysql_library_init() or indirectly through mysql_init(). This should be done prior to any other client library call.

To connect to the server, call mysql_init() to initialize a connection handler, then call mysql_real_connect() with that handler (along with other information such as the host name, user name, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1 in versions of the API older than 5.0.3, or 0 in newer versions. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. You can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior. When you are done with the connection, call mysql_close() to terminate it. Do not use the handler after it has been closed.

While a connection is active, the client may send SQL statements to the server using mysql_query() or mysql_real_query(). The difference between the two is that mysql_query() expects the query to be specified as a null-terminated string whereas mysql_real_query() expects a counted string. If the string contains binary data (which may include null bytes), you must use mysql_real_query().

For each non-SELECT query (for example, INSERT, UPDATE, DELETE), you can find out how many rows were changed (affected) by calling mysql_affected_rows().

For SELECT queries, you retrieve the selected rows as a result set. (Note that some statements are SELECT-like in that they return rows. These include SHOW, DESCRIBE, and EXPLAIN. Treat these statements the same way as SELECT statements.)

There are two ways for a client to process result sets. One way is to retrieve the entire result set all at once by calling mysql_store_result(). This function acquires from the server all the rows returned by the query and stores them in the client. The second way is for the client to initiate a row-by-row result set retrieval by calling mysql_use_result(). This function initializes the retrieval, but does not actually get any rows from the server.

In both cases, you access rows by calling mysql_fetch_row(). With mysql_store_result(), mysql_fetch_row() accesses rows that have previously been fetched from the server. With mysql_use_result(), mysql_fetch_row() actually retrieves the row from the server. Information about the size of the data in each row is available by calling mysql_fetch_lengths().

After you are done with a result set, call mysql_free_result() to free the memory used for it.

The two retrieval mechanisms are complementary. Choose the approach that is most appropriate for each client application. In practice, clients tend to use mysql_store_result() more commonly.

An advantage of mysql_store_result() is that because the rows have all been fetched to the client, you not only can access rows sequentially, you can move back and forth in the result set using mysql_data_seek() or mysql_row_seek() to change the current row position within the result set. You can also find out how many rows there are by calling mysql_num_rows(). On the other hand, the memory requirements for mysql_store_result() may be very high for large result sets and you are more likely to encounter out-of-memory conditions.

An advantage of mysql_use_result() is that the client requires less memory for the result set because it maintains only one row at a time (and because there is less allocation overhead, mysql_use_result() can be faster). Disadvantages are that you must process each row quickly to avoid tying up the server, you do not have random access to rows within the result set (you can only access rows sequentially), and the number of rows in the result set is unknown until you have retrieved them all. Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for.

The API makes it possible for clients to respond appropriately to statements (retrieving rows only as necessary) without knowing whether the statement is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the statement was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the statement returned no data (indicating that it was an INSERT, UPDATE, DELETE, and so forth), and was not expected to return rows. If mysql_field_count() is nonzero, the statement should have returned rows, but did not. This indicates that the statement was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.

Both mysql_store_result() and mysql_use_result() enable you to obtain information about the fields that make up the result set (the number of fields, their names and types, and so forth). You can access field information sequentially within the row by calling mysql_fetch_field() repeatedly, or by field number within the row by calling mysql_fetch_field_direct(). The current field cursor position may be changed by calling mysql_field_seek(). Setting the field cursor affects subsequent calls to mysql_fetch_field(). You can also get information for fields all at once by calling mysql_fetch_fields().

For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, enabling you to determine when an error occurred and what it was.

27.7.6 C API Function Descriptions

27.7.6.1 mysql_affected_rows()
27.7.6.2 mysql_autocommit()
27.7.6.3 mysql_change_user()
27.7.6.4 mysql_character_set_name()
27.7.6.5 mysql_close()
27.7.6.6 mysql_commit()
27.7.6.7 mysql_connect()
27.7.6.8 mysql_create_db()
27.7.6.9 mysql_data_seek()
27.7.6.10 mysql_debug()
27.7.6.11 mysql_drop_db()
27.7.6.12 mysql_dump_debug_info()
27.7.6.13 mysql_eof()
27.7.6.14 mysql_errno()
27.7.6.15 mysql_error()
27.7.6.16 mysql_escape_string()
27.7.6.17 mysql_fetch_field()
27.7.6.18 mysql_fetch_field_direct()
27.7.6.19 mysql_fetch_fields()
27.7.6.20 mysql_fetch_lengths()
27.7.6.21 mysql_fetch_row()
27.7.6.22 mysql_field_count()
27.7.6.23 mysql_field_seek()
27.7.6.24 mysql_field_tell()
27.7.6.25 mysql_free_result()
27.7.6.26 mysql_get_character_set_info()
27.7.6.27 mysql_get_client_info()
27.7.6.28 mysql_get_client_version()
27.7.6.29 mysql_get_host_info()
27.7.6.30 mysql_get_option()
27.7.6.31 mysql_get_proto_info()
27.7.6.32 mysql_get_server_info()
27.7.6.33 mysql_get_server_version()
27.7.6.34 mysql_get_ssl_cipher()
27.7.6.35 mysql_hex_string()
27.7.6.36 mysql_info()
27.7.6.37 mysql_init()
27.7.6.38 mysql_insert_id()
27.7.6.39 mysql_kill()
27.7.6.40 mysql_library_end()
27.7.6.41 mysql_library_init()
27.7.6.42 mysql_list_dbs()
27.7.6.43 mysql_list_fields()
27.7.6.44 mysql_list_processes()
27.7.6.45 mysql_list_tables()
27.7.6.46 mysql_more_results()
27.7.6.47 mysql_next_result()
27.7.6.48 mysql_num_fields()
27.7.6.49 mysql_num_rows()
27.7.6.50 mysql_options()
27.7.6.51 mysql_options4()
27.7.6.52 mysql_ping()
27.7.6.53 mysql_query()
27.7.6.54 mysql_real_connect()
27.7.6.55 mysql_real_escape_string()
27.7.6.56 mysql_real_escape_string_quote()
27.7.6.57 mysql_real_query()
27.7.6.58 mysql_refresh()
27.7.6.59 mysql_reload()
27.7.6.60 mysql_reset_connection()
27.7.6.61 mysql_rollback()
27.7.6.62 mysql_row_seek()
27.7.6.63 mysql_row_tell()
27.7.6.64 mysql_select_db()
27.7.6.65 mysql_session_track_get_first()
27.7.6.66 mysql_session_track_get_next()
27.7.6.67 mysql_set_character_set()
27.7.6.68 mysql_set_local_infile_default()
27.7.6.69 mysql_set_local_infile_handler()
27.7.6.70 mysql_set_server_option()
27.7.6.71 mysql_shutdown()
27.7.6.72 mysql_sqlstate()
27.7.6.73 mysql_ssl_set()
27.7.6.74 mysql_stat()
27.7.6.75 mysql_store_result()
27.7.6.76 mysql_thread_id()
27.7.6.77 mysql_use_result()
27.7.6.78 mysql_warning_count()

This section describes C API functions other than those used for prepared statements or the replication stream interface. For information about those, see Section 27.7.10, “C API Prepared Statement Function Descriptions”, and C API Binary Log Function Descriptions.

In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value.

Functions that return a value generally return a pointer or an integer. Unless specified otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or nonzero to indicate an error. Note that nonzero means just that. Unless the function description says otherwise, do not test against a value other than zero:

if (result)                   /* correct */
    ... error ...

if (result < 0)               /* incorrect */
    ... error ...

if (result == -1)             /* incorrect */
    ... error ...

When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can find out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().

27.7.6.1 mysql_affected_rows()

my_ulonglong mysql_affected_rows(MYSQL *mysql)

Description

mysql_affected_rows() may be called immediately after executing a statement with mysql_query() or mysql_real_query(). It returns the number of rows changed, deleted, or inserted by the last statement if it was an UPDATE, DELETE, or INSERT. For SELECT statements, mysql_affected_rows() works like mysql_num_rows().

For UPDATE statements, the affected-rows value by default is the number of rows actually changed. If you specify the CLIENT_FOUND_ROWS flag to mysql_real_connect() when connecting to mysqld, the affected-rows value is the number of rows found; that is, matched by the WHERE clause.

For REPLACE statements, the affected-rows value is 2 if the new row replaced an old row, because in this case, one row was inserted after the duplicate was deleted.

For INSERT ... ON DUPLICATE KEY UPDATE statements, the affected-rows value per row is 1 if the row is inserted as a new row, 2 if an existing row is updated, and 0 if an existing row is set to its current values. If you specify the CLIENT_FOUND_ROWS flag, the affected-rows value is 1 (not 0) if an existing row is set to its current values.

Following a CALL statement for a stored procedure, mysql_affected_rows() returns the value that it would return for the last statement executed within the procedure, or 0 if that statement would return -1. Within the procedure, you can use ROW_COUNT() at the SQL level to obtain the affected-rows value for individual statements.

In MySQL 5.7, mysql_affected_rows() returns a meaningful value for a wider range of statements. For details, see the description for ROW_COUNT() in Section 12.15, “Information Functions”.

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_affected_rows() was called prior to calling mysql_store_result().

Because mysql_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

Errors

None.

Example
char *stmt = "UPDATE products SET cost=cost*1.25
              WHERE group=10";
mysql_query(&mysql,stmt);
printf("%ld products updated",
(long) mysql_affected_rows(&mysql));

27.7.6.2 mysql_autocommit()

my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)

Description

Sets autocommit mode on if mode is 1, off if mode is 0.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

None.

27.7.6.3 mysql_change_user()

my_bool mysql_change_user(MYSQL *mysql, const char *user, const char *password, const char *db)

Description

Changes the user and causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that include no explicit database specifier.

mysql_change_user() fails if the connected user cannot be authenticated or does not have permission to use the database. In this case, the user and database are not changed.

Pass a db parameter of NULL if you do not want to have a default database.

This function resets the session state as if one had done a new connect and reauthenticated. (See Section 27.7.19, “C API Automatic Reconnection Control”.) It always performs a ROLLBACK of any active transactions, closes and drops all temporary tables, and unlocks all locked tables. Session system variables are reset to the values of the corresponding global system variables. Prepared statements are released and HANDLER variables are closed. Locks acquired with GET_LOCK() are released. These effects occur even if the user did not change.

To reset the connection state in a more lightweight manner without changing the user, use mysql_reset_connection().

Return Values

Zero for success. Nonzero if an error occurred.

Errors

The same that you can get from mysql_real_connect(), plus:

Example
if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
   fprintf(stderr, "Failed to change user.  Error: %s\n",
           mysql_error(&mysql));
}

27.7.6.4 mysql_character_set_name()

const char *mysql_character_set_name(MYSQL *mysql)

Description

Returns the default character set name for the current connection.

Return Values

The default character set name

Errors

None.

27.7.6.5 mysql_close()

void mysql_close(MYSQL *mysql)

Description

Closes a previously opened connection. mysql_close() also deallocates the connection handler pointed to by mysql if the handler was allocated automatically by mysql_init() or mysql_connect(). Do not use the handler after it has been closed.

Return Values

None.

Errors

None.

27.7.6.6 mysql_commit()

my_bool mysql_commit(MYSQL *mysql)

Description

Commits the current transaction.

The action of this function is subject to the value of the completion_type system variable. In particular, if the value of completion_type is RELEASE (or 2), the server performs a release after terminating a transaction and closes the client connection. Call mysql_close() from the client program to close the connection from the client side.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

None.

27.7.6.7 mysql_connect()

MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)

Description

This function is deprecated. Use mysql_real_connect() instead.

mysql_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().

The meanings of the parameters are the same as for the corresponding parameters for mysql_real_connect() with the difference that the connection parameter may be NULL. In this case, the C API allocates memory for the connection structure automatically and frees it when you call mysql_close(). The disadvantage of this approach is that you cannot retrieve an error message if the connection fails. (To get error information from mysql_errno() or mysql_error(), you must provide a valid MYSQL pointer.)

Return Values

Same as for mysql_real_connect().

Errors

Same as for mysql_real_connect().

27.7.6.8 mysql_create_db()

int mysql_create_db(MYSQL *mysql, const char *db)

Description

Creates the database named by the db parameter.

This function is deprecated. Use mysql_query() to issue an SQL CREATE DATABASE statement instead.

Return Values

Zero for success. Nonzero if an error occurred.

Errors
Example
if(mysql_create_db(&mysql, "my_database"))
{
   fprintf(stderr, "Failed to create new database.  Error: %s\n",
           mysql_error(&mysql));
}

27.7.6.9 mysql_data_seek()

void mysql_data_seek(MYSQL_RES *result, my_ulonglong offset)

Description

Seeks to an arbitrary row in a query result set. The offset value is a row number. Specify a value in the range from 0 to mysql_num_rows(result)-1.

This function requires that the result set structure contains the entire result of the query, so mysql_data_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

None.

Errors

None.

27.7.6.10 mysql_debug()

void mysql_debug(const char *debug)

Description

Does a DBUG_PUSH with the given string. mysql_debug() uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. See Section 28.5.3, “The DBUG Package”.

Return Values

None.

Errors

None.

Example

The call shown here causes the client library to generate a trace file in /tmp/client.trace on the client machine:

mysql_debug("d:t:O,/tmp/client.trace");

27.7.6.11 mysql_drop_db()

int mysql_drop_db(MYSQL *mysql, const char *db)

Description

Drops the database named by the db parameter.

This function is deprecated. Use mysql_query() to issue an SQL DROP DATABASE statement instead.

Return Values

Zero for success. Nonzero if an error occurred.

Errors
Example
if(mysql_drop_db(&mysql, "my_database"))
  fprintf(stderr, "Failed to drop the database: Error: %s\n",
mysql_error(&mysql));

27.7.6.12 mysql_dump_debug_info()

int mysql_dump_debug_info(MYSQL *mysql)

Description

Instructs the server to write debugging information to the error log. The connected user must have the SUPER privilege.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.13 mysql_eof()

my_bool mysql_eof(MYSQL_RES *result)

Description

This function is deprecated. mysql_errno() or mysql_error() may be used instead.

mysql_eof() determines whether the last row of a result set has been read.

If you acquire a result set from a successful call to mysql_store_result(), the client receives the entire set in one operation. In this case, a NULL return from mysql_fetch_row() always means the end of the result set has been reached and it is unnecessary to call mysql_eof(). When used with mysql_store_result(), mysql_eof() always returns true.

On the other hand, if you use mysql_use_result() to initiate a result set retrieval, the rows of the set are obtained from the server one by one as you call mysql_fetch_row() repeatedly. Because an error may occur on the connection during this process, a NULL return value from mysql_fetch_row() does not necessarily mean the end of the result set was reached normally. In this case, you can use mysql_eof() to determine what happened. mysql_eof() returns a nonzero value if the end of the result set was reached and zero if an error occurred.

Historically, mysql_eof() predates the standard MySQL error functions mysql_errno() and mysql_error(). Because those error functions provide the same information, their use is preferred over mysql_eof(), which is deprecated. (In fact, they provide more information, because mysql_eof() returns only a boolean value whereas the error functions indicate a reason for the error when one occurs.)

Return Values

Zero for success. Nonzero if the end of the result set has been reached.

Errors

None.

Example

The following example shows how you might use mysql_eof():

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(!mysql_eof(result))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

However, you can achieve the same effect with the standard MySQL error functions:

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(mysql_errno(&mysql))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

27.7.6.14 mysql_errno()

unsigned int mysql_errno(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_errno() returns the error code for the most recently invoked API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix B, Errors, Error Codes, and Common Problems.

Note

Some functions such as mysql_fetch_row() do not set mysql_errno() if they succeed. A rule of thumb is that all functions that have to ask the server for information reset mysql_errno() if they succeed.

MySQL-specific error numbers returned by mysql_errno() differ from SQLSTATE values returned by mysql_sqlstate(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist
Return Values

An error code value for the last mysql_xxx() call, if it failed. zero means no error occurred.

Errors

None.

27.7.6.15 mysql_error()

const char *mysql_error(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_error() returns a null-terminated string containing the error message for the most recently invoked API function that failed. If a function did not fail, the return value of mysql_error() may be the previous error or an empty string to indicate no error.

A rule of thumb is that all functions that have to ask the server for information reset mysql_error() if they succeed.

For functions that reset mysql_error(), either of these two tests can be used to check for an error:

if(*mysql_error(&mysql))
{
  // an error occurred
}

if(mysql_error(&mysql)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. You can choose error messages in several different languages. See Section 10.12, “Setting the Error Message Language”.

Return Values

A null-terminated character string that describes the error. An empty string if no error occurred.

Errors

None.

27.7.6.16 mysql_escape_string()

Note

Do not use this function. mysql_escape_string() does not have arguments that enable it to respect the current character set or the quoting context. Use mysql_real_escape_string_quote() instead.

27.7.6.17 mysql_fetch_field()

MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)

Description

Returns the definition of one column of a result set as a MYSQL_FIELD structure. Call this function repeatedly to retrieve information about all columns in the result set. mysql_fetch_field() returns NULL when no more fields are left.

mysql_fetch_field() is reset to return information about the first field each time you execute a new SELECT query. The field returned by mysql_fetch_field() is also affected by calls to mysql_field_seek().

If you've called mysql_query() to perform a SELECT on a table but have not called mysql_store_result(), MySQL returns the default blob length (8KB) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8KB size is chosen because MySQL does not know the maximum length for the BLOB. This should be made configurable sometime.) Once you've retrieved the result set, field->max_length contains the length of the largest value for this column in the specific query.

Return Values

The MYSQL_FIELD structure for the current column. NULL if no columns are left.

Errors

None.

Example
MYSQL_FIELD *field;

while((field = mysql_fetch_field(result)))
{
    printf("field name %s\n", field->name);
}

27.7.6.18 mysql_fetch_field_direct()

MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)

Description

Given a field number fieldnr for a column within a result set, returns that column's field definition as a MYSQL_FIELD structure. Use this function to retrieve the definition for an arbitrary column. Specify a value for fieldnr in the range from 0 to mysql_num_fields(result)-1.

Return Values

The MYSQL_FIELD structure for the specified column.

Errors

None.

Example
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;

num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
    field = mysql_fetch_field_direct(result, i);
    printf("Field %u is %s\n", i, field->name);
}

27.7.6.19 mysql_fetch_fields()

MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)

Description

Returns an array of all MYSQL_FIELD structures for a result set. Each structure provides the field definition for one column of the result set.

Return Values

An array of MYSQL_FIELD structures for all columns of a result set.

Errors

None.

Example
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;

num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
   printf("Field %u is %s\n", i, fields[i].name);
}

27.7.6.20 mysql_fetch_lengths()

unsigned long *mysql_fetch_lengths(MYSQL_RES *result)

Description

Returns the lengths of the columns of the current row within a result set. If you plan to copy field values, this length information is also useful for optimization, because you can avoid calling strlen(). In addition, if the result set contains binary data, you must use this function to determine the size of the data, because strlen() returns incorrect results for any field containing null characters.

The length for empty columns and for columns containing NULL values is zero. To see how to distinguish these two cases, see the description for mysql_fetch_row().

Return Values

An array of unsigned long integers representing the size of each column (not including any terminating null bytes). NULL if an error occurred.

Errors

mysql_fetch_lengths() is valid only for the current row of the result set. It returns NULL if you call it before calling mysql_fetch_row() or after retrieving all rows in the result.

Example
MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;

row = mysql_fetch_row(result);
if (row)
{
    num_fields = mysql_num_fields(result);
    lengths = mysql_fetch_lengths(result);
    for(i = 0; i < num_fields; i++)
    {
         printf("Column %u is %lu bytes in length.\n",
                i, lengths[i]);
    }
}

27.7.6.21 mysql_fetch_row()

MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)

Description

mysql_fetch_row() retrieves the next row of a result set:

The number of values in the row is given by mysql_num_fields(result). If row holds the return value from a call to mysql_fetch_row(), pointers to the values are accessed as row[0] to row[mysql_num_fields(result)-1]. NULL values in the row are indicated by NULL pointers.

The lengths of the field values in the row may be obtained by calling mysql_fetch_lengths(). Empty fields and fields containing NULL both have length 0; you can distinguish these by checking the pointer for the field value. If the pointer is NULL, the field is NULL; otherwise, the field is empty.

Return Values

A MYSQL_ROW structure for the next row, or NULL. The meaning of a NULL return depends on which function was called preceding mysql_fetch_row():

Errors

Errors are not reset between calls to mysql_fetch_row()

Example
MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;

num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
   unsigned long *lengths;
   lengths = mysql_fetch_lengths(result);
   for(i = 0; i < num_fields; i++)
   {
       printf("[%.*s] ", (int) lengths[i],
              row[i] ? row[i] : "NULL");
   }
   printf("\n");
}

27.7.6.22 mysql_field_count()

unsigned int mysql_field_count(MYSQL *mysql)

Description

Returns the number of columns for the most recent query on the connection.

The normal use of this function is when mysql_store_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a nonempty result. This enables the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 27.7.20.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if(mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
        else // mysql_store_result() should have returned data
        {
            fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
    }
}

An alternative is to replace the mysql_field_count(&mysql) call with mysql_errno(&mysql). In this case, you are checking directly for an error from mysql_store_result() rather than inferring from the value of mysql_field_count() whether the statement was a SELECT.

27.7.6.23 mysql_field_seek()

MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)

Description

Sets the field cursor to the given offset. The next call to mysql_fetch_field() retrieves the field definition of the column associated with that offset.

To seek to the beginning of a row, pass an offset value of zero.

Return Values

The previous value of the field cursor.

Errors

None.

27.7.6.24 mysql_field_tell()

MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)

Description

Returns the position of the field cursor used for the last mysql_fetch_field(). This value can be used as an argument to mysql_field_seek().

Return Values

The current offset of the field cursor.

Errors

None.

27.7.6.25 mysql_free_result()

void mysql_free_result(MYSQL_RES *result)

Description

mysql_free_result() frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), and so forth. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().

Do not attempt to access a result set after freeing it.

Return Values

None.

Errors

None.

27.7.6.26 mysql_get_character_set_info()

void mysql_get_character_set_info(MYSQL *mysql, MY_CHARSET_INFO *cs)

Description

This function provides information about the default client character set. The default character set may be changed with the mysql_set_character_set() function.

Example

This example shows the fields that are available in the MY_CHARSET_INFO structure:

if (!mysql_set_character_set(&mysql, "utf8"))
{
    MY_CHARSET_INFO cs;
    mysql_get_character_set_info(&mysql, &cs);
    printf("character set information:\n");
    printf("character set+collation number: %d\n", cs.number);
    printf("character set name: %s\n", cs.name);
    printf("collation name: %s\n", cs.csname);
    printf("comment: %s\n", cs.comment);
    printf("directory: %s\n", cs.dir);
    printf("multi byte character min. length: %d\n", cs.mbminlen);
    printf("multi byte character max. length: %d\n", cs.mbmaxlen);
}

27.7.6.27 mysql_get_client_info()

const char *mysql_get_client_info(void)

Description

Returns a string that represents the MySQL client library version (for example, "5.7.30").

The function value is the version of MySQL that provides the client library. For more information, see Section 27.7.3.5, “C API Server Version and Client Library Version”.

Return Values

A character string that represents the MySQL client library version.

Errors

None.

27.7.6.28 mysql_get_client_version()

unsigned long mysql_get_client_version(void)

Description

Returns an integer that represents the MySQL client library version. The value has the format XYYZZ where X is the major version, YY is the release level (or minor version), and ZZ is the sub-version within the release level:

major_version*10000 + release_level*100 + sub_version

For example, "5.7.30" is returned as 50730.

The function value is the version of MySQL that provides the client library. For more information, see Section 27.7.3.5, “C API Server Version and Client Library Version”.

Return Values

An integer that represents the MySQL client library version.

Errors

None.

27.7.6.29 mysql_get_host_info()

const char *mysql_get_host_info(MYSQL *mysql)

Description

Returns a string describing the type of connection in use, including the server host name.

Return Values

A character string representing the server host name and the connection type.

Errors

None.

27.7.6.30 mysql_get_option()

int mysql_get_option(MYSQL *mysql, enum mysql_option option, const void *arg)

Description

Returns the current value of an option settable using mysql_options(). The value should be treated as read only.

The option argument is the option for which you want its value. The arg argument is a pointer to a variable in which to store the option value. arg must be a pointer to a variable of the type appropriate for the option argument. The following table shows which variable type to use for each option value.

arg Type Applicable option Values
unsigned int MYSQL_OPT_CONNECT_TIMEOUT, MYSQL_OPT_PROTOCOL, MYSQL_OPT_READ_TIMEOUT, MYSQL_OPT_RETRY_COUNT, MYSQL_OPT_SSL_MODE, MYSQL_OPT_WRITE_TIMEOUT
unsigned long MYSQL_OPT_MAX_ALLOWED_PACKET, MYSQL_OPT_NET_BUFFER_LENGTH
my_bool MYSQL_ENABLE_CLEARTEXT_PLUGIN, MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS, MYSQL_OPT_GET_SERVER_PUBLIC_KEY, MYSQL_OPT_GUESS_CONNECTION, MYSQL_OPT_LOCAL_INFILE, MYSQL_OPT_RECONNECT, MYSQL_OPT_SSL_ENFORCE, MYSQL_OPT_SSL_VERIFY_SERVER_CERT, MYSQL_OPT_USE_EMBEDDED_CONNECTION, MYSQL_OPT_USE_REMOTE_CONNECTION, MYSQL_REPORT_DATA_TRUNCATION, MYSQL_SECURE_AUTH
const char * MYSQL_DEFAULT_AUTH, MYSQL_OPT_BIND, MYSQL_OPT_SSL_CA, MYSQL_OPT_SSL_CAPATH, MYSQL_OPT_SSL_CERT, MYSQL_OPT_SSL_CIPHER, MYSQL_OPT_SSL_CRL, MYSQL_OPT_SSL_CRLPATH, MYSQL_OPT_SSL_KEY, MYSQL_OPT_TLS_VERSION, MYSQL_PLUGIN_DIR, MYSQL_READ_DEFAULT_FILE, MYSQL_READ_DEFAULT_GROUP, MYSQL_SERVER_PUBLIC_KEY, MYSQL_SET_CHARSET_DIR, MYSQL_SET_CHARSET_NAME, MYSQL_SET_CLIENT_IP, MYSQL_SHARED_MEMORY_BASE_NAME
argument not used MYSQL_OPT_COMPRESS
cannot be queried (error is returned) MYSQL_INIT_COMMAND, MYSQL_OPT_CONNECT_ATTR_DELETE, MYSQL_OPT_CONNECT_ATTR_RESET, MYSQL_OPT_NAMED_PIPE
Return Values

Zero for success. Nonzero if an error occurred; this occurs for option values that cannot be queried.

Example

The following call tests the MYSQL_OPT_RECONNECT option. After the call returns successfully, the value of reconnect is true or false to indicate whether automatic reconnection is enabled.

my_bool reconnect;

if (mysql_get_option(mysql, MYSQL_OPT_RECONNECT, &reconnect))
fprintf(stderr, "mysql_get_options() failed\n");

27.7.6.31 mysql_get_proto_info()

unsigned int mysql_get_proto_info(MYSQL *mysql)

Description

Returns the protocol version used by current connection.

Return Values

An unsigned integer representing the protocol version used by the current connection.

Errors

None.

27.7.6.32 mysql_get_server_info()

const char *mysql_get_server_info(MYSQL *mysql)

Description

Returns a string that represents the MySQL server version (for example, "5.7.30").

Return Values

A character string that represents the MySQL server version.

Errors

None.

27.7.6.33 mysql_get_server_version()

unsigned long mysql_get_server_version(MYSQL *mysql)

Description

Returns an integer that represents the MySQL server version. The value has the format XYYZZ where X is the major version, YY is the release level (or minor version), and ZZ is the sub-version within the release level:

major_version*10000 + release_level*100 + sub_version

For example, "5.7.30" is returned as 50730.

This function is useful in client programs for determining whether some version-specific server capability exists.

Return Values

An integer that represents the MySQL server version.

Errors

None.

27.7.6.34 mysql_get_ssl_cipher()

const char *mysql_get_ssl_cipher(MYSQL *mysql)

Description

mysql_get_ssl_cipher() returns the encryption cipher used for the given connection to the server. mysql is the connection handler returned from mysql_init().

Return Values

A string naming the encryption cipher used for the connection, or NULL if the connection is not encrypted.

27.7.6.35 mysql_hex_string()

unsigned long mysql_hex_string(char *to, const char *from, unsigned long length)

Description

This function creates a legal SQL string for use in an SQL statement. See Section 9.1.1, “String Literals”.

The string in the from argument is encoded in hexadecimal format, with each character encoded as two hexadecimal digits. The result is placed in the to argument, followed by a terminating null byte.

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. When mysql_hex_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null byte.

The return value can be placed into an SQL statement using either X'value' or 0xvalue format. However, the return value does not include the X'...' or 0x. The caller must supply whichever of those is desired.

Example
char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
end = strmov(end,"X'");
end += mysql_hex_string(end,"What is this",12);
end = strmov(end,"',X'");
end += mysql_hex_string(end,"binary data: \0\r\n",16);
end = strmov(end,"')");

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the libmysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the encoded string that is placed into to, not including the terminating null character.

Errors

None.

27.7.6.36 mysql_info()

const char *mysql_info(MYSQL *mysql)

Description

Retrieves a string providing information about the most recently executed statement, but only for the statements listed here. For other statements, mysql_info() returns NULL. The format of the string varies depending on the type of statement, as described here. The numbers are illustrative only; the string contains values appropriate for the statement.

  • INSERT INTO ... SELECT ...

    String format: Records: 100 Duplicates: 0 Warnings: 0

  • INSERT INTO ... VALUES (...),(...),(...)...

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • LOAD DATA

    String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0

  • ALTER TABLE

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • UPDATE

    String format: Rows matched: 40 Changed: 40 Warnings: 0

mysql_info() returns a non-NULL value for INSERT ... VALUES only for the multiple-row form of the statement (that is, only if multiple value lists are specified).

Return Values

A character string representing additional information about the most recently executed statement. NULL if no information is available for the statement.

Errors

None.

27.7.6.37 mysql_init()

MYSQL *mysql_init(MYSQL *mysql)

Description

Allocates or initializes a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initializes, and returns a new object. Otherwise, the object is initialized and the address of the object is returned. If mysql_init() allocates a new object, it is freed when mysql_close() is called to close the connection.

In a nonmultithreaded environment, mysql_init() invokes mysql_library_init() automatically as necessary. However, mysql_library_init() is not thread-safe in a multithreaded environment, and thus neither is mysql_init(). Before calling mysql_init(), either call mysql_library_init() prior to spawning any threads, or use a mutex to protect the mysql_library_init() call. This should be done prior to any other client library call.

Return Values

An initialized MYSQL* handler. NULL if there was insufficient memory to allocate a new object.

Errors

In case of insufficient memory, NULL is returned.

27.7.6.38 mysql_insert_id()

my_ulonglong mysql_insert_id(MYSQL *mysql)

Description

Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field, or have used INSERT or UPDATE to set a column value with LAST_INSERT_ID(expr).

The return value of mysql_insert_id() is always zero unless explicitly updated under one of the following conditions:

The return value of mysql_insert_id() can be simplified to the following sequence:

  1. If there is an AUTO_INCREMENT column, and an automatically generated value was successfully inserted, return the first such value.

  2. If LAST_INSERT_ID(expr) occurred in the statement, return expr, even if there was an AUTO_INCREMENT column in the affected table.

  3. The return value varies depending on the statement used. When called after an INSERT statement:

    • If there is an AUTO_INCREMENT column in the table, and there were some explicit values for this column that were successfully inserted into the table, return the last of the explicit values.

    When called after an INSERT ... ON DUPLICATE KEY UPDATE statement:

    • If there is an AUTO_INCREMENT column in the table and there were some explicit successfully inserted values or some updated values, return the last of the inserted or updated values.

mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you must save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.

The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.

The LAST_INSERT_ID() SQL function will contain the value of the first automatically generated value that was successfully inserted. LAST_INSERT_ID() is not reset between statements because the value of that function is maintained in the server. Another difference from mysql_insert_id() is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific nonspecial value. See Section 12.15, “Information Functions”.

mysql_insert_id() returns 0 following a CALL statement for a stored procedure that generates an AUTO_INCREMENT value because in this case mysql_insert_id() applies to CALL and not the statement within the procedure. Within the procedure, you can use LAST_INSERT_ID() at the SQL level to obtain the AUTO_INCREMENT value.

The reason for the differences between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide more exact information about what happens to the AUTO_INCREMENT column.

Note

The OK packet used in the client/server protocol holds information such as is used for session state tracking. When clients read the OK packet to know whether there is a session state change, this resets values such as the last insert ID and the number of affected rows. Such changes cause mysql_insert_id() to return 0 after execution of commands including but not necessarily limited to COM_PING, COM_REFRESH, and COM_INIT_DB.

Return Values

Described in the preceding discussion.

Errors
  • ER_AUTO_INCREMENT_CONFLICT

    A user-specified AUTO_INCREMENT value in a multi INSERT statement falls within the range between the current AUTO_INCREMENT value and the sum of the current and number of rows affected values.

27.7.6.39 mysql_kill()

int mysql_kill(MYSQL *mysql, unsigned long pid)

Description
Note

As of MySQL 5.7.11, mysql_kill() is deprecated and will be removed in a future version of MySQL. Instead, use mysql_query() to execute a KILL statement.

Asks the server to kill the thread specified by pid.

This function is deprecated. Use mysql_query() to issue an SQL KILL statement instead.

mysql_kill() cannot handle values larger than 32 bits, but to guard against killing the wrong thread returns an error in these cases:

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.40 mysql_library_end()

void mysql_library_end(void)

Description

This function finalizes the MySQL library. Call it when you are done using the library (for example, after disconnecting from the server). The action taken by the call depends on whether your application is linked to the MySQL client library or the MySQL embedded server library. For a client program linked against the libmysqlclient library by using the -lmysqlclient flag, mysql_library_end() performs some memory management to clean up. For an embedded server application linked against the libmysqld library by using the -lmysqld flag, mysql_library_end() shuts down the embedded server and then cleans up.

Note

To avoid memory leaks after the application is done using the library (for example, after closing the connection to the server), be sure to call mysql_library_end() explicitly. This enables memory managment to be performed to clean up and free resources used by the library.

For usage information, see Section 27.7.5, “C API Function Overview”, and Section 27.7.6.41, “mysql_library_init()”.

27.7.6.41 mysql_library_init()

int mysql_library_init(int argc, char **argv, char **groups)

Description

Call this function to initialize the MySQL client library before you call any other MySQL function, whether your application is a regular client program or uses the embedded server. If the application uses the embedded server, this call starts the server and initializes any subsystems (mysys, InnoDB, and so forth) that the server uses.

Note

To avoid memory leaks after the application is done using the library (for example, after closing the connection to the server), be sure to call mysql_library_end() explicitly. This enables memory managment to be performed to clean up and free resources used by the library. See Section 27.7.6.40, “mysql_library_end()”.

The choice of whether the application operates as a regular client or uses the embedded server depends on whether you use the libmysqlclient or libmysqld library at link time to produce the final executable. For additional information, see Section 27.7.5, “C API Function Overview”.

In a nonmultithreaded environment, the call to mysql_library_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, mysql_library_init() is not thread-safe in a multithreaded environment, and thus neither is mysql_init(), which calls mysql_library_init(). You must either call mysql_library_init() prior to spawning any threads, or else use a mutex to protect the call, whether you invoke mysql_library_init() or indirectly through mysql_init(). Do this prior to any other client library call.

The argc and argv arguments are analogous to the arguments to main(), and enable passing of options to the embedded server. For convenience, argc may be 0 (zero) if there are no command-line arguments for the server. This is the usual case for applications intended for use only as regular (nonembedded) clients, and the call typically is written as mysql_library_init(0, NULL, NULL).

#include <mysql.h>
#include <stdlib.h>

int main(void) {
  if (mysql_library_init(0, NULL, NULL)) {
    fprintf(stderr, "could not initialize MySQL client library\n");
    exit(1);
  }

  /* Use any MySQL API functions here */

  mysql_library_end();

  return EXIT_SUCCESS;
}

When arguments are to be passed (argc is greater than 0), the first element of argv is ignored (it typically contains the program name). mysql_library_init() makes a copy of the arguments so it is safe to destroy argv or groups after the call.

For embedded applications, if you want to connect to an external server without starting the embedded server, you have to specify a negative value for argc.

The groups argument is an array of strings that indicate the groups in option files from which to read options. See Section 4.2.2.2, “Using Option Files”. Make the final entry in the array NULL. For convenience, if the groups argument itself is NULL, the [server] and [embedded] groups are used by default.

#include <mysql.h>
#include <stdlib.h>

static char *server_args[] = {
  "this_program",       /* this string is not used */
  "--datadir=.",
  "--key_buffer_size=32M"
};
static char *server_groups[] = {
  "embedded",
  "server",
  "this_program_SERVER",
  (char *)NULL
};

int main(void) {
  if (mysql_library_init(sizeof(server_args) / sizeof(char *),
                        server_args, server_groups)) {
    fprintf(stderr, "could not initialize MySQL client library\n");
    exit(1);
  }

  /* Use any MySQL API functions here */

  mysql_library_end();

  return EXIT_SUCCESS;
}
Return Values

Zero for success. Nonzero if an error occurred.

27.7.6.42 mysql_list_dbs()

MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of database names on the server that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all databases. Calling mysql_list_dbs() is similar to executing the query SHOW DATABASES [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

27.7.6.43 mysql_list_fields()

MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)

Description
Note

As of MySQL 5.7.11, mysql_list_fields() is deprecated and will be removed in a future version of MySQL. Instead, use mysql_query() to execute a SHOW COLUMNS statement.

Returns an empty result set for which the metadata provides information about the columns in the given table that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all fields. Calling mysql_list_fields() is similar to executing the query SHOW COLUMNS FROM tbl_name [LIKE wild].

It is preferable to use SHOW COLUMNS FROM tbl_name instead of mysql_list_fields().

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors
Example
int i;
MYSQL_RES *tbl_cols = mysql_list_fields(mysql, "mytbl", "f%");

unsigned int field_cnt = mysql_num_fields(tbl_cols);
printf("Number of columns: %d\n", field_cnt);

for (i=0; i < field_cnt; ++i)
{
  /* col describes i-th column of the table */
  MYSQL_FIELD *col = mysql_fetch_field_direct(tbl_cols, i);
  printf ("Column %d: %s\n", i, col->name);
}
mysql_free_result(tbl_cols);

27.7.6.44 mysql_list_processes()

MYSQL_RES *mysql_list_processes(MYSQL *mysql)

Description
Note

As of MySQL 5.7.11, mysql_list_processes() is deprecated and will be removed in a future version of MySQL. Instead, use mysql_query() to execute a SHOW PROCESSLIST statement.

Returns a result set describing the current server threads. This is the same kind of information as that reported by mysqladmin processlist or a SHOW PROCESSLIST query.

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

27.7.6.45 mysql_list_tables()

MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of table names in the current database that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all tables. Calling mysql_list_tables() is similar to executing the query SHOW TABLES [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

27.7.6.46 mysql_more_results()

my_bool mysql_more_results(MYSQL *mysql)

Description

This function is used when you execute multiple statements specified as a single statement string, or when you execute CALL statements, which can return multiple result sets.

mysql_more_results() true if more results exist from the currently executed statement, in which case the application must call mysql_next_result() to fetch the results.

Return Values

TRUE (1) if more results exist. FALSE (0) if no more results exist.

In most cases, you can call mysql_next_result() instead to test whether more results exist and initiate retrieval if so.

See Section 27.7.15, “C API Multiple Statement Execution Support”, and Section 27.7.6.47, “mysql_next_result()”.

Errors

None.

27.7.6.47 mysql_next_result()

int mysql_next_result(MYSQL *mysql)

Description

mysql_next_result() is used when you execute multiple statements specified as a single statement string, or when you use CALL statements to execute stored procedures, which can return multiple result sets.

mysql_next_result() reads the next statement result and returns a status to indicate whether more results exist. If mysql_next_result() returns an error, there are no more results.

Before each call to mysql_next_result(), you must call mysql_free_result() for the current statement if it is a statement that returned a result set (rather than just a result status).

After calling mysql_next_result() the state of the connection is as if you had called mysql_real_query() or mysql_query() for the next statement. This means that you can call mysql_store_result(), mysql_warning_count(), mysql_affected_rows(), and so forth.

If your program uses CALL statements to execute stored procedures, the CLIENT_MULTI_RESULTS flag must be enabled. This is because each CALL returns a result to indicate the call status, in addition to any result sets that might be returned by statements executed within the procedure. Because CALL can return multiple results, process them using a loop that calls mysql_next_result() to determine whether there are more results.

CLIENT_MULTI_RESULTS can be enabled when you call mysql_real_connect(), either explicitly by passing the CLIENT_MULTI_RESULTS flag itself, or implicitly by passing CLIENT_MULTI_STATEMENTS (which also enables CLIENT_MULTI_RESULTS). In MySQL 5.7, CLIENT_MULTI_RESULTS is enabled by default.

It is also possible to test whether there are more results by calling mysql_more_results(). However, this function does not change the connection state, so if it returns true, you must still call mysql_next_result() to advance to the next result.

For an example that shows how to use mysql_next_result(), see Section 27.7.15, “C API Multiple Statement Execution Support”.

Return Values
Return Value Description
0 Successful and there are more results
-1 Successful and there are no more results
>0 An error occurred
Errors

27.7.6.48 mysql_num_fields()

unsigned int mysql_num_fields(MYSQL_RES *result)

To pass a MYSQL* argument instead, use unsigned int mysql_field_count(MYSQL *mysql).

Description

Returns the number of columns in a result set.

You can get the number of columns either from a pointer to a result set or to a connection handler. You would use the connection handler if mysql_store_result() or mysql_use_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a nonempty result. This enables the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 27.7.20.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if (mysql_errno(&mysql))
        {
           fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
        else if (mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
    }
}

An alternative (if you know that your query should have returned a result set) is to replace the mysql_errno(&mysql) call with a check whether mysql_field_count(&mysql) returns 0. This happens only if something went wrong.

27.7.6.49 mysql_num_rows()

my_ulonglong mysql_num_rows(MYSQL_RES *result)

Description

Returns the number of rows in the result set.

The use of mysql_num_rows() depends on whether you use mysql_store_result() or mysql_use_result() to return the result set. If you use mysql_store_result(), mysql_num_rows() may be called immediately. If you use mysql_use_result(), mysql_num_rows() does not return the correct value until all the rows in the result set have been retrieved.

mysql_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_affected_rows().

Return Values

The number of rows in the result set.

Errors

None.

27.7.6.50 mysql_options()

int mysql_options(MYSQL *mysql, enum mysql_option option, const void *arg)

Description

Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options. To retrieve option values, use mysql_get_option().

Call mysql_options() after mysql_init() and before mysql_connect() or mysql_real_connect().

The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, specify a pointer to the value of the integer as the arg argument.

Options for information such as SSL certificate and key files are used to establish an encrypted connection if such connections are available, but do not enforce any requirement that the connection obtained be encrypted. To require an encrypted connection, use the technique described in Section 27.7.14, “C API Encrypted Connection Support”.

The following list describes the possible options, their effect, and how arg is used for each option. For option descriptions that indicate arg is unused, its value is irrelevant; it is conventional to pass 0. Several of the options apply only when the application is linked against the libmysqld embedded server library and are unused for applications linked against the libmysqlclient client library.

  • MYSQL_DEFAULT_AUTH (argument type: char *)

    The name of the authentication plugin to use.

  • MYSQL_ENABLE_CLEARTEXT_PLUGIN (argument type: my_bool *)

    Enable the mysql_clear_password cleartext authentication plugin. See Section 6.4.1.6, “Client-Side Cleartext Pluggable Authentication”.

  • MYSQL_INIT_COMMAND (argument type: char *)

    SQL statement to execute when connecting to the MySQL server. Automatically re-executed if reconnection occurs.

  • MYSQL_OPT_BIND (argument: char *)

    The network interface from which to connect to the server. This is used when the client host has multiple network interfaces. The argument is a host name or IP address (specified as a string).

  • MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS (argument type: my_bool *)

    Indicate whether the client can handle expired passwords. See Section 6.2.12, “Server Handling of Expired Passwords”.

  • MYSQL_OPT_COMPRESS (argument: not used)

    Compress all information sent between the client and the server if possible. See Section 4.2.5, “Connection Compression Control”.

  • MYSQL_OPT_CONNECT_ATTR_DELETE (argument type: char *)

    Given a key name, this option deletes a key-value pair from the current set of connection attributes to pass to the server at connect time. The argument is a pointer to a null-terminated string naming the key. Comparison of the key name with existing keys is case-sensitive.

    See also the description for the MYSQL_OPT_CONNECT_ATTR_RESET option, as well as the description for the MYSQL_OPT_CONNECT_ATTR_ADD option in the description of the mysql_options4() function. That function description also includes a usage example.

    The Performance Schema exposes connection attributes through the session_connect_attrs and session_account_connect_attrs tables. See Section 25.12.9, “Performance Schema Connection Attribute Tables”.

  • MYSQL_OPT_CONNECT_ATTR_RESET (argument not used)

    This option resets (clears) the current set of connection attributes to pass to the server at connect time.

    See also the description for the MYSQL_OPT_CONNECT_ATTR_DELETE option, as well as the description for the MYSQL_OPT_CONNECT_ATTR_ADD option in the description of the mysql_options4() function. That function description also includes a usage example.

    The Performance Schema exposes connection attributes through the session_connect_attrs and session_account_connect_attrs tables. See Section 25.12.9, “Performance Schema Connection Attribute Tables”.

  • MYSQL_OPT_CONNECT_TIMEOUT (argument type: unsigned int *)

    The connect timeout in seconds.

  • MYSQL_OPT_GET_SERVER_PUBLIC_KEY (argument type: my_bool *)

    Enables the client to request from the server the public key required for RSA key pair-based password exchange. This option applies to clients that authenticate with the caching_sha2_password authentication plugin. For that plugin, the server does not send the public key unless requested. This option is ignored for accounts that do not authenticate with that plugin. It is also ignored if RSA-based password exchange is not used, as is the case when the client connects to the server using a secure connection.

    If MYSQL_SERVER_PUBLIC_KEY is given and specifies a valid public key file, it takes precedence over MYSQL_OPT_GET_SERVER_PUBLIC_KEY.

    For information about the caching_sha2_password plugin, see Section 6.4.1.4, “Caching SHA-2 Pluggable Authentication”.

    This option was added in MySQL 5.7.23.

  • MYSQL_OPT_GUESS_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this option enables the library to guess whether to use the embedded server or a remote server. Guess means that if the host name is set and is not localhost, it uses a remote server. This behavior is the default. MYSQL_OPT_USE_EMBEDDED_CONNECTION and MYSQL_OPT_USE_REMOTE_CONNECTION can be used to override it. This option is ignored for applications linked against the libmysqlclient client library.

  • MYSQL_OPT_LOCAL_INFILE (argument type: optional pointer to unsigned int)

    This option affects client-side LOCAL capability for LOAD DATA operations. By default, LOCAL capability is determined by the default compiled into the MySQL client library (see Section 13.2.6, “LOAD DATA Statement”). To control this capability explicitly, invoke mysql_options() to set the MYSQL_OPT_LOCAL_INFILE option:

    • LOCAL is disabled if the pointer points to an unsigned int that has a zero value.

    • LOCAL is enabled if no pointer is given or if the pointer points to an unsigned int that has a nonzero value.

    Successful use of a LOCAL load operation by a client also requires that the server permits it.

  • MYSQL_OPT_MAX_ALLOWED_PACKET (argument: unsigned long *)

    This option sets the max_allowed_packet system variable. If the mysql argument is non-NULL, the call sets the session system variable value for that session. If mysql is NULL, the call sets the global system variable value.

  • MYSQL_OPT_NAMED_PIPE (argument: not used)

    Use a named pipe to connect to the MySQL server on Windows, if the server permits named-pipe connections.

  • MYSQL_OPT_NET_BUFFER_LENGTH (argument: unsigned long *)

    This option sets the net_buffer_length system variable. If the mysql argument is non-NULL, the call sets the session system variable value for that session. If mysql is NULL, the call sets the global system variable value.

  • MYSQL_OPT_PROTOCOL (argument type: unsigned int *)

    Type of protocol to use. Specify one of the enum values of mysql_protocol_type defined in mysql.h.

  • MYSQL_OPT_READ_TIMEOUT (argument type: unsigned int *)

    The timeout in seconds for each attempt to read from the server. There are retries if necessary, so the total effective timeout value is three times the option value. You can set the value so that a lost connection can be detected earlier than the TCP/IP Close_Wait_Timeout value of 10 minutes.

  • MYSQL_OPT_RECONNECT (argument type: my_bool *)

    Enable or disable automatic reconnection to the server if the connection is found to have been lost. Reconnect is off by default; this option provides a way to set reconnection behavior explicitly. See Section 27.7.19, “C API Automatic Reconnection Control”.

  • MYSQL_OPT_RETRY_COUNT (argument type: unsigned int *)

    The retry count for I/O-related system calls that are interrupted while connecting to the server or communicating with it. If this option is not specified, the default value is 1 (1 retry if the initial call is interrupted for 2 tries total).

    This option can be used only by clients that link against a C client library compiiled with NDB Cluster support. It is available as of MySQL NDB Cluster 7.5.1.

  • MYSQL_OPT_SSL_CA (argument type: char *)

    The path name of the Certificate Authority (CA) certificate file. This option, if used, must specify the same certificate used by the server.

  • MYSQL_OPT_SSL_CAPATH (argument type: char *)

    The path name of the directory that contains trusted SSL CA certificate files.

  • MYSQL_OPT_SSL_CERT (argument type: char *)

    The path name of the client public key certificate file.

  • MYSQL_OPT_SSL_CIPHER (argument type: char *)

    The list of permissible ciphers for SSL encryption.

  • MYSQL_OPT_SSL_CRL (argument type: char *)

    The path name of the file containing certificate revocation lists.

  • MYSQL_OPT_SSL_CRLPATH (argument type: char *)

    The path name of the directory that contains files containing certificate revocation lists.

  • MYSQL_OPT_SSL_ENFORCE (argument type: my_bool *)

    Whether to require the connection to use SSL. If enabled and an encrypted connection cannot be established, the connection attempt fails.

    This option is deprecated as of MySQL 5.7.11 and is removed in MySQL 8.0. Instead, use MYSQL_OPT_SSL_MODE with a value of SSL_MODE_REQUIRED.

  • MYSQL_OPT_SSL_KEY (argument type: char *)

    The path name of the client private key file.

  • MYSQL_OPT_SSL_MODE (argument type: unsigned int *)

    The security state to use for the connection to the server: SSL_MODE_DISABLED, SSL_MODE_PREFERRED, SSL_MODE_REQUIRED, SSL_MODE_VERIFY_CA, SSL_MODE_VERIFY_IDENTITY. If this option is not specified, the default is SSL_MODE_PREFERRED. These modes are the permitted values of the mysql_ssl_mode enumeration defined in mysql.h. For more information about the security states, see the description of --ssl-mode in Command Options for Encrypted Connections.

    This option was added in MySQL 5.7.11.

  • MYSQL_OPT_SSL_VERIFY_SERVER_CERT (argument type: my_bool *)

    Enable or disable verification of the server's Common Name identity in its certificate against the host name used when connecting to the server. The connection is rejected if there is a mismatch. For encrypted connections, this feature can be used to prevent man-in-the-middle attacks. Identity verification is disabled by default.

    This option does not work with self-signed certificates, which do not contain the server name as the Common Name value.

    This option is deprecated as of MySQL 5.7.11 and is removed in MySQL 8.0. Instead, use MYSQL_OPT_SSL_MODE with a value of SSL_MODE_VERIFY_IDENTITY.

  • MYSQL_OPT_TLS_VERSION (argument type: char *)

    Which protocols the client permits for encrypted connections. The value is a list of one or more comma-separated protocol versions. The protocols that can be named for this option depend on the SSL library used to compile MySQL. For details, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

    This option was added in MySQL 5.7.10.

  • MYSQL_OPT_USE_EMBEDDED_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this option forces the use of the embedded server for the connection. It is ignored for applications linked against the libmysqlclient client library.

  • MYSQL_OPT_USE_REMOTE_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this option forces the use of a remote server for the connection. It is ignored for applications linked against the libmysqlclient client library.

  • MYSQL_OPT_USE_RESULT (argument: not used)

    This option is unused.

  • MYSQL_OPT_WRITE_TIMEOUT (argument type: unsigned int *)

    The timeout in seconds for each attempt to write to the server. There is a retry if necessary, so the total effective timeout value is two times the option value.

  • MYSQL_PLUGIN_DIR (argument type: char *)

    The directory in which to look for client plugins.

  • MYSQL_READ_DEFAULT_FILE (argument type: char *)

    Read options from the named option file instead of from my.cnf.

  • MYSQL_READ_DEFAULT_GROUP (argument type: char *)

    Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE.

  • MYSQL_REPORT_DATA_TRUNCATION (argument type: my_bool *)

    Enable or disable reporting of data truncation errors for prepared statements using the error member of MYSQL_BIND structures. (Default: enabled.)

  • MYSQL_SECURE_AUTH (argument type: my_bool *)

    Whether to connect to a server that does not support the password hashing used in MySQL 4.1.1 and later. This option is enabled by default.

  • MYSQL_SERVER_PUBLIC_KEY (argument type: char *)

    The path name to a file containing a client-side copy of the public key required by the server for RSA key pair-based password exchange. The file must be in PEM format. This option applies to clients that authenticate with the sha256_password authentication plugin. This option is ignored for accounts that do not authenticate with one of those plugins. It is also ignored if RSA-based password exchange is not used, as is the case when the client connects to the server using a secure connection.

    If MYSQL_SERVER_PUBLIC_KEY is given and specifies a valid public key file, it takes precedence over MYSQL_OPT_GET_SERVER_PUBLIC_KEY.

    For information about the sha256_password and caching_sha2_password plugins, see Section 6.4.1.5, “SHA-256 Pluggable Authentication”, and Section 6.4.1.4, “Caching SHA-2 Pluggable Authentication”.

  • MYSQL_SET_CHARSET_DIR (argument type: char *)

    The path name of the directory that contains character set definition files.

  • MYSQL_SET_CHARSET_NAME (argument type: char *)

    The name of the character set to use as the default character set. The argument can be MYSQL_AUTODETECT_CHARSET_NAME to cause the character set to be autodetected based on the operating system setting (see Section 10.4, “Connection Character Sets and Collations”).

  • MYSQL_SET_CLIENT_IP (argument type: char *)

    For an application linked against the libmysqld embedded server library (when libmysqld is compiled with authentication support), this option means that the user is considered to have connected from the specified IP address (specified as a string) for authentication purposes. It is ignored for applications linked against the libmysqlclient client library.

  • MYSQL_SHARED_MEMORY_BASE_NAME (argument type: char *)

    The name of the shared-memory object for communication to the server on Windows, if the server supports shared-memory connections. Specify the same value as used for the shared_memory_base_name system variable. of the mysqld server you want to connect to.

The client group is always read if you use MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.

The specified group in the option file may contain the following options.

Option Description
character-sets-dir=dir_name The directory where character sets are installed.
compress Use the compressed client/server protocol.
connect-timeout=seconds The connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server.
database=db_name Connect to this database if no database was specified in the connect command.
debug Debug options.
default-character-set=charset_name The default character set to use.
disable-local-infile Disable use of LOAD DATA LOCAL.
enable-cleartext-plugin Enable the mysql_clear_password cleartext authentication plugin.
host=host_name Default host name.
init-command=stmt Statement to execute when connecting to MySQL server. Automatically re-executed if reconnection occurs.
interactive-timeout=seconds Same as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See Section 27.7.6.54, “mysql_real_connect()”.
local-infile[={0|1}] If no argument or nonzero argument, enable use of LOAD DATA LOCAL; otherwise disable.
max_allowed_packet=bytes Maximum size of packet that client can read from server.
multi-queries, multi-results Enable multiple result sets from multiple-statement executions or stored procedures.
multi-statements Enable the client to send multiple statements in a single string (separated by ; characters).
password=password Default password.
pipe Use named pipes to connect to a MySQL server on Windows.
port=port_num Default port number.
protocol={TCP|SOCKET|PIPE|MEMORY} The protocol to use when connecting to the server.
return-found-rows Tell mysql_info() to return found rows instead of updated rows when using UPDATE.
shared-memory-base-name=name Shared-memory name to use to connect to server.
socket={file_name|pipe_name} Default socket file.
ssl-ca=file_name Certificate Authority file.
ssl-capath=dir_name Certificate Authority directory.
ssl-cert=file_name Certificate file.
ssl-cipher=cipher_list Permissible SSL ciphers.
ssl-key=file_name Key file.
timeout=seconds Like connect-timeout.
user Default user.

timeout has been replaced by connect-timeout, but timeout is still supported for backward compatibility.

For more information about option files used by MySQL programs, see Section 4.2.2.2, “Using Option Files”.

Return Values

Zero for success. Nonzero if you specify an unknown option.

Example

The following mysql_options() calls request the use of compression in the client/server protocol, cause options to be read from the [odbc] group in option files, and disable transaction autocommit mode:

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
mysql_options(&mysql,MYSQL_INIT_COMMAND,"SET autocommit=0");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

27.7.6.51 mysql_options4()

int mysql_options4(MYSQL *mysql, enum mysql_option option, const void *arg1, const void *arg2)

Description

mysql_options4() is similar to mysql_options() but has an extra fourth argument so that two values can be passed for the option specified in the second argument.

The following list describes the permitted options, their effect, and how arg1 and arg2 are used.

  • MYSQL_OPT_CONNECT_ATTR_ADD (argument types: char *, char *)

    This option adds an attribute key-value pair to the current set of connection attributes to pass to the server at connect time. Both arguments are pointers to null-terminated strings. The first and second strings indicate the key and value, respectively. If the key is empty or already exists in the current set of connection attributes, an error occurs. Comparison of the key name with existing keys is case-sensitive.

    Key names that begin with an underscore (_) are reserved for internal use and should not be created by application programs. This convention permits new attributes to be introduced by MySQL without colliding with application attributes.

    mysql_options4() imposes a limit of 64KB on the aggregate size of connection attribute data it will accept. For calls that cause this limit to be exceeded, a CR_INVALID_PARAMETER_NO error occurs. Attribute size-limit checks also occur on the server side. For details, see Section 25.12.9, “Performance Schema Connection Attribute Tables”, which also describes how the Performance Schema exposes connection attributes through the session_connect_attrs and session_account_connect_attrs tables.

    See also the descriptions for the MYSQL_OPT_CONNECT_ATTR_RESET and MYSQL_OPT_CONNECT_ATTR_DELETE options in the description of the mysql_options() function.

Return Values

Zero for success. Nonzero if you specify an unknown option.

Errors
Example

This example demonstrates the calls that specify connection attributes:

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_CONNECT_ATTR_RESET, 0);
mysql_options4(&mysql,MYSQL_OPT_CONNECT_ATTR_ADD, "key1", "value1");
mysql_options4(&mysql,MYSQL_OPT_CONNECT_ATTR_ADD, "key2", "value2");
mysql_options4(&mysql,MYSQL_OPT_CONNECT_ATTR_ADD, "key3", "value3");
mysql_options(&mysql,MYSQL_OPT_CONNECT_ATTR_DELETE, "key1");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
        mysql_error(&mysql));
}

27.7.6.52 mysql_ping()

int mysql_ping(MYSQL *mysql)

Description

Checks whether the connection to the server is working. If the connection has gone down and auto-reconnect is enabled an attempt to reconnect is made. If the connection is down and auto-reconnect is disabled, mysql_ping() returns an error.

Auto-reconnect is disabled by default. To enable it, call mysql_options() with the MYSQL_OPT_RECONNECT option. For details, see Section 27.7.6.50, “mysql_options()”.

mysql_ping() can be used by clients that remain idle for a long while, to check whether the server has closed the connection and reconnect if necessary.

If mysql_ping()) does cause a reconnect, there is no explicit indication of it. To determine whether a reconnect occurs, call mysql_thread_id() to get the original connection identifier before calling mysql_ping(), then call mysql_thread_id() again to see whether the identifier has changed.

If reconnect occurs, some characteristics of the connection will have been reset. For details about these characteristics, see Section 27.7.19, “C API Automatic Reconnection Control”.

Return Values

Zero if the connection to the server is active. Nonzero if an error occurred. A nonzero return does not indicate whether the MySQL server itself is down; the connection might be broken for other reasons such as network problems.

Errors

27.7.6.53 mysql_query()

int mysql_query(MYSQL *mysql, const char *stmt_str)

Description

Executes the SQL statement pointed to by the null-terminated string stmt_str. Normally, the string must consist of a single SQL statement without a terminating semicolon (;) or \g. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 27.7.15, “C API Multiple Statement Execution Support”.

mysql_query() cannot be used for statements that contain binary data; you must use mysql_real_query() instead. (Binary data may contain the \0 character, which mysql_query() interprets as the end of the statement string.)

If you want to know whether the statement returns a result set, you can use mysql_field_count() to check for this. See Section 27.7.6.22, “mysql_field_count()”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.54 mysql_real_connect()

MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)

Description

mysql_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any other API functions that require a valid MYSQL connection handler structure.

The parameters are specified as follows:

  • For the first parameter, specify the address of an existing MYSQL structure. Before calling mysql_real_connect(), call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See Section 27.7.6.50, “mysql_options()”.

  • The value of host may be either a host name or an IP address. The client attempts to connect as follows:

    • If host is NULL or the string "localhost", a connection to the local host is assumed:

      • On Windows, the client connects using a shared-memory connection, if the server has shared-memory connections enabled.

      • On Unix, the client connects using a Unix socket file. The unix_socket parameter or the MYSQL_UNIX_PORT environment variable may be used to specify the socket name.

    • On Windows, if host is ".", or TCP/IP is not enabled and no unix_socket is specified or the host is empty, the client connects using a named pipe, if the server has named-pipe connections enabled. If named-pipe connections are not enabled, an error occurs.

    • Otherwise, TCP/IP is used.

    You can also influence the type of connection to use with the MYSQL_OPT_PROTOCOL or MYSQL_OPT_NAMED_PIPE options to mysql_options(). The type of connection must be supported by the server.

  • The user parameter contains the user's MySQL login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current user name must be specified explicitly. See the Connector/ODBC section of Chapter 27, Connectors and APIs.

  • The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field are checked for a match. This enables the database administrator to set up the MySQL privilege system in such a way that users get different privileges depending on whether they have specified a password.

    Note

    Do not attempt to encrypt the password before calling mysql_real_connect(); password encryption is handled automatically by the client API.

  • The user and passwd parameters use whatever character set has been configured for the MYSQL object. By default, this is latin1, but can be changed by calling mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "charset_name") prior to connecting.

  • db is the database name. If db is not NULL, the connection sets the default database to this value.

  • If port is not 0, the value is used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection.

  • If unix_socket is not NULL, the string specifies the socket or named pipe to use. Note that the host parameter determines the type of the connection.

  • The value of client_flag is usually 0, but can be set to a combination of the following flags to enable certain features:

    • CAN_HANDLE_EXPIRED_PASSWORDS: The client can handle expired passwords. For more information, see Section 6.2.12, “Server Handling of Expired Passwords”.

    • CLIENT_COMPRESS: Use compression in the client/server protocol.

    • CLIENT_FOUND_ROWS: Return the number of found (matched) rows, not the number of changed rows.

    • CLIENT_IGNORE_SIGPIPE: Prevents the client library from installing a SIGPIPE signal handler. This can be used to avoid conflicts with a handler that the application has already installed.

    • CLIENT_IGNORE_SPACE: Permit spaces after function names. Makes all functions names reserved words.

    • CLIENT_INTERACTIVE: Permit interactive_timeout seconds of inactivity (rather than wait_timeout seconds) before closing the connection. The client's session wait_timeout variable is set to the value of the session interactive_timeout variable.

    • CLIENT_LOCAL_FILES: Enable LOAD DATA LOCAL handling.

    • CLIENT_MULTI_RESULTS: Tell the server that the client can handle multiple result sets from multiple-statement executions or stored procedures. This flag is automatically enabled if CLIENT_MULTI_STATEMENTS is enabled. See the note following this table for more information about this flag.

    • CLIENT_MULTI_STATEMENTS: Tell the server that the client may send multiple statements in a single string (separated by ; characters). If this flag is not set, multiple-statement execution is disabled. See the note following this table for more information about this flag.

    • CLIENT_NO_SCHEMA Do not permit db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.

    • CLIENT_ODBC: Unused.

    • CLIENT_SSL: Use SSL (encrypted protocol). Do not set this option within an application program; it is set internally in the client library. Instead, use mysql_options() or mysql_ssl_set() before calling mysql_real_connect().

    • CLIENT_REMEMBER_OPTIONS Remember options specified by calls to mysql_options(). Without this option, if mysql_real_connect() fails, you must repeat the mysql_options() calls before trying to connect again. With this option, the mysql_options() calls need not be repeated.

If your program uses CALL statements to execute stored procedures, the CLIENT_MULTI_RESULTS flag must be enabled. This is because each CALL returns a result to indicate the call status, in addition to any result sets that might be returned by statements executed within the procedure. Because CALL can return multiple results, process them using a loop that calls mysql_next_result() to determine whether there are more results.

CLIENT_MULTI_RESULTS can be enabled when you call mysql_real_connect(), either explicitly by passing the CLIENT_MULTI_RESULTS flag itself, or implicitly by passing CLIENT_MULTI_STATEMENTS (which also enables CLIENT_MULTI_RESULTS). In MySQL 5.7, CLIENT_MULTI_RESULTS is enabled by default.

If you enable CLIENT_MULTI_STATEMENTS or CLIENT_MULTI_RESULTS, process the result for every call to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 27.7.15, “C API Multiple Statement Execution Support”.

For some parameters, it is possible to have the value taken from an option file rather than from an explicit value in the mysql_real_connect() call. To do this, call mysql_options() with the MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP option before calling mysql_real_connect(). Then, in the mysql_real_connect() call, specify the no-value value for each parameter to be read from an option file:

  • For host, specify a value of NULL or the empty string ("").

  • For user, specify a value of NULL or the empty string.

  • For passwd, specify a value of NULL. (For the password, a value of the empty string in the mysql_real_connect() call cannot be overridden in an option file, because the empty string indicates explicitly that the MySQL account must have an empty password.)

  • For db, specify a value of NULL or the empty string.

  • For port, specify a value of 0.

  • For unix_socket, specify a value of NULL.

If no value is found in an option file for a parameter, its default value is used as indicated in the descriptions given earlier in this section.

Return Values

A MYSQL* connection handler if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.

Errors
Example
MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

By using mysql_options() the MySQL client library reads the [client] and [your_prog_name] sections in the my.cnf file which ensures that your program works, even if someone has set up MySQL in some nonstandard way.

Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1 in versions of the API older than 5.0.3, or 0 in newer versions. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. You can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior.

27.7.6.55 mysql_real_escape_string()

unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)

Description

This function creates a legal SQL string for use in an SQL statement. See Section 9.1.1, “String Literals”.

Note

mysql_real_escape_string() fails and produces an CR_INSECURE_API_ERR error if the NO_BACKSLASH_ESCAPES SQL mode is enabled. In this case, the function cannot escape quote characters except by doubling them, and to do this properly, it must know more information about the quoting context than is available. Instead, use mysql_real_escape_string_quote(), which takes an extra argument for specifying the quoting context.

The mysql argument must be a valid, open connection because character escaping depends on the character set in use by the server.

The string in the from argument is encoded to produce an escaped SQL string, taking into account the current character set of the connection. The result is placed in the to argument, followed by a terminating null byte.

Characters encoded are \, ', ", NUL (ASCII 0), \n, \r, and Control+Z. Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. mysql_real_escape_string() quotes the other characters to make them easier to read in log files. For comparison, see the quoting rules for literal strings and the QUOTE() SQL function in Section 9.1.1, “String Literals”, and Section 12.7, “String Functions and Operators”.

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and there must be room for the terminating null byte.) When mysql_real_escape_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null byte.

If you must change the character set of the connection, use the mysql_set_character_set() function rather than executing a SET NAMES (or SET CHARACTER SET) statement. mysql_set_character_set() works like SET NAMES but also affects the character set used by mysql_real_escape_string(), which SET NAMES does not.

Example

The following example inserts two escaped strings into an INSERT statement, each within single quote characters:

char query[1000],*end;

end = my_stpcpy(query,"INSERT INTO test_table VALUES('");
end += mysql_real_escape_string(&mysql,end,"What is this",12);
end = my_stpcpy(end,"','");
end += mysql_real_escape_string(&mysql,end,"binary data: \0\r\n",16);
end = my_stpcpy(end,"')");

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The my_stpcpy() function used in the example is included in the libmysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the encoded string that is placed into the to argument, not including the terminating null byte, or -1 if an error occurs.

Because mysql_real_escape_string() returns an unsigned value, you can check for -1 by comparing the return value to (unsigned long)-1 (or to (unsigned long)~0, which is equivalent).

Errors

27.7.6.56 mysql_real_escape_string_quote()

unsigned long mysql_real_escape_string_quote(MYSQL *mysql, char *to, const char *from, unsigned long length, char quote)

Description

This function creates a legal SQL string for use in an SQL statement. See Section 9.1.1, “String Literals”.

The mysql argument must be a valid, open connection because character escaping depends on the character set in use by the server.

The string in the from argument is encoded to produce an escaped SQL string, taking into account the current character set of the connection. The result is placed in the to argument, followed by a terminating null byte.

Characters encoded are \, ', ", NUL (ASCII 0), \n, \r, Control+Z, and `. Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. mysql_real_escape_string_quote() quotes the other characters to make them easier to read in log files. For comparison, see the quoting rules for literal strings and the QUOTE() SQL function in Section 9.1.1, “String Literals”, and Section 12.7, “String Functions and Operators”.

Note

If the ANSI_QUOTES SQL mode is enabled, mysql_real_escape_string_quote() cannot be used to escape double quote characters for use within double-quoted identifiers. (The function cannot tell whether the mode is enabled to determine the proper escaping character.)

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and there must be room for the terminating null byte.) When mysql_real_escape_string_quote() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null byte.

The quote argument indicates the context in which the escaped string is to be placed. Suppose that you intend to escape the from argument and insert the escaped string (designated here by str) into one of the following statements:

1) SELECT * FROM table WHERE name = 'str'
2) SELECT * FROM table WHERE name = "str"
3) SELECT * FROM `str` WHERE id = 103

To perform escaping properly for each statement, call mysql_real_escape_string_quote() as follows, where the final argument indicates the quoting context:

1) len = mysql_real_escape_string_quote(&mysql,to,from,from_len,'\'');
2) len = mysql_real_escape_string_quote(&mysql,to,from,from_len,'"');
3) len = mysql_real_escape_string_quote(&mysql,to,from,from_len,'`');

If you must change the character set of the connection, use the mysql_set_character_set() function rather than executing a SET NAMES (or SET CHARACTER SET) statement. mysql_set_character_set() works like SET NAMES but also affects the character set used by mysql_real_escape_string_quote(), which SET NAMES does not.

Example

The following example inserts two escaped strings into an INSERT statement, each within single quote characters:

char query[1000],*end;

end = my_stpcpy(query,"INSERT INTO test_table VALUES('");
end += mysql_real_escape_string_quote(&mysql,end,"What is this",12,'\'');
end = my_stpcpy(end,"','");
end += mysql_real_escape_string_quote(&mysql,end,"binary data: \0\r\n",16,'\'');
end = my_stpcpy(end,"')");

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The my_stpcpy() function used in the example is included in the libmysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the encoded string that is placed into the to argument, not including the terminating null byte.

Errors

None.

27.7.6.57 mysql_real_query()

int mysql_real_query(MYSQL *mysql, const char *stmt_str, unsigned long length)

Description

mysql_real_query() executes the SQL statement pointed to by stmt_str, a string length bytes long. Normally, the string must consist of a single SQL statement without a terminating semicolon (;) or \g. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 27.7.15, “C API Multiple Statement Execution Support”.

mysql_query() cannot be used for statements that contain binary data; you must use mysql_real_query() instead. (Binary data may contain the \0 character, which mysql_query() interprets as the end of the statement string.) In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the statement string.

If you want to know whether the statement returns a result set, you can use mysql_field_count() to check for this. See Section 27.7.6.22, “mysql_field_count()”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.58 mysql_refresh()

int mysql_refresh(MYSQL *mysql, unsigned int options)

Description
Note

As of MySQL 5.7.11, mysql_refresh() is deprecated and will be removed in a future version of MySQL. Instead, use mysql_query() to execute a FLUSH statement.

This function flushes tables or caches, or resets replication server information. The connected user must have the RELOAD privilege.

The options argument is a bitmask composed from any combination of the following values. Multiple values can be OR'ed together to perform multiple operations with a single call.

  • REFRESH_GRANT

    Refresh the grant tables, like FLUSH PRIVILEGES.

  • REFRESH_LOG

    Flush the logs, like FLUSH LOGS.

  • REFRESH_TABLES

    Flush the table cache, like FLUSH TABLES.

  • REFRESH_HOSTS

    Flush the host cache, like FLUSH HOSTS.

  • REFRESH_STATUS

    Reset status variables, like FLUSH STATUS.

  • REFRESH_THREADS

    Flush the thread cache.

  • REFRESH_SLAVE

    On a slave replication server, reset the master server information and restart the slave, like RESET SLAVE.

  • REFRESH_MASTER

    On a master replication server, remove the binary log files listed in the binary log index and truncate the index file, like RESET MASTER.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.59 mysql_reload()

int mysql_reload(MYSQL *mysql)

Description

Asks the MySQL server to reload the grant tables. The connected user must have the RELOAD privilege.

This function is deprecated. Use mysql_query() to issue an SQL FLUSH PRIVILEGES statement instead.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.60 mysql_reset_connection()

int mysql_reset_connection(MYSQL *mysql)

Description

Resets the connection to clear the session state.

mysql_reset_connection() has effects similar to mysql_change_user() or an auto-reconnect except that the connection is not closed and reopened, and reauthentication is not done. See Section 27.7.6.3, “mysql_change_user()”, and Section 27.7.19, “C API Automatic Reconnection Control”.

The connection-related state is affected as follows:

  • Any active transactions are rolled back and autocommit mode is reset.

  • All table locks are released.

  • All TEMPORARY tables are closed (and dropped).

  • Session system variables are reinitialized to the values of the corresponding global system variables, including system variables that are set implicitly by statements such as SET NAMES.

  • User variable settings are lost.

  • Prepared statements are released.

  • HANDLER variables are closed.

  • The value of LAST_INSERT_ID() is reset to 0.

  • Locks acquired with GET_LOCK() are released.

Return Values

Zero for success. Nonzero if an error occurred.

27.7.6.61 mysql_rollback()

my_bool mysql_rollback(MYSQL *mysql)

Description

Rolls back the current transaction.

The action of this function is subject to the value of the completion_type system variable. In particular, if the value of completion_type is RELEASE (or 2), the server performs a release after terminating a transaction and closes the client connection. Call mysql_close() from the client program to close the connection from the client side.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

None.

27.7.6.62 mysql_row_seek()

MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a query result set. The offset value is a row offset, typically a value returned from mysql_row_tell() or from mysql_row_seek(). This value is not a row number; to seek to a row within a result set by number, use mysql_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_row_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_row_seek().

Errors

None.

27.7.6.63 mysql_row_tell()

MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)

Description

Returns the current position of the row cursor for the last mysql_fetch_row(). This value can be used as an argument to mysql_row_seek().

Use mysql_row_tell() only after mysql_store_result(), not after mysql_use_result().

Return Values

The current offset of the row cursor.

Errors

None.

27.7.6.64 mysql_select_db()

int mysql_select_db(MYSQL *mysql, const char *db)

Description

Causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that include no explicit database specifier.

mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database or some object within it.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.65 mysql_session_track_get_first()

int mysql_session_track_get_first(MYSQL *mysql, enum enum_session_state_type type, const char **data, size_t *length)

Description

MySQL implements a session tracker mechanism whereby the server returns information about session state changes to clients. To control which notifications the server provides about state changes, client applications set system variables having names of the form session_track_xxx, such as session_track_state_change, session_track_schema, and session_track_system_variables. See Section 5.1.14, “Server Tracking of Client Session State Changes”.

Change notification occurs in the MySQL client/server protocol, which includes tracker information in OK packets so that session state changes can be detected. To enable client applications to extract state-change information from OK packets, the MySQL C API provides a pair of functions:

The mysql_session_track_get_first() parameters are used as follows. These descriptions also apply to mysql_session_track_get_next(), which takes the same parameters.

  • mysql: The connection handler.

  • type: The tracker type indicating what kind of information to retrieve. Permitted tracker values are the members of the enum_session_state_type enumeration defined in mysql_com.h:

    enum enum_session_state_type
    {
      SESSION_TRACK_SYSTEM_VARIABLES,            /* Session system variables */
      SESSION_TRACK_SCHEMA,                      /* Current schema */
      SESSION_TRACK_STATE_CHANGE,                /* Session state changes */
      SESSION_TRACK_GTIDS,                       /* GTIDs */
      SESSION_TRACK_TRANSACTION_CHARACTERISTICS, /* Transaction characteristics */
      SESSION_TRACK_TRANSACTION_STATE            /* Transaction state */
    };

    The members of that enumeration may change over time as MySQL implements additional session-information trackers. To make it easy for applications to loop over all possible tracker types regardless of the number of members, the SESSION_TRACK_BEGIN and SESSION_TRACK_END symbols are defined to be equal to the first and last members of the enum_session_state_type enumeration. The example code shown later in this section demonstrates this technique. (Of course, if the enumeration members change, you must recompile your application to enable it to take account of new trackers.)

  • data: The address of a const char * variable. Following a successful call, this variable points to the returned data, which should be considered read only.

  • length: The address of a size_t variable. Following a successful call, this variable contains the length of the data pointed to by the data parameter.

The following discussion describes how to interpret the data and length values according to the type value. It also indicates which system variable enables notifications for each tracker type.

  • SESSION_TRACK_SCHEMA: This tracker type indicates that the default schema has been set. data is a string containing the new default schema name. length is the string length.

    To enable notifications for this tracker type, enable the session_track_schema system variable.

  • SESSION_TRACK_SYSTEM_VARIABLES: This tracker type indicates that one or more tracked session system variables have been assigned a value. When a session system variable is assigned, two values per variable are returned (in separate calls). For the first call, data is a string containing the variable name and length is the string length. For the second call, data is a string containing the variable value and length is the string length.

    By default, notification is enabled for these session system variables:

    To change the default notification for this tracker type, set the session_track_schema system variable to a list of comma-separated variables for which to track changes, or * to track changes for all variables. To disable notification of session variable assignments, set session_track_system_variables to the empty string.

  • SESSION_TRACK_STATE_CHANGE: This tracker type indicates a change to some tracked attribute of session state. data is a byte containing a boolean flag that indicates whether session state changes occurred. length should be 1. The flag is represented as an ASCII value, not a binary (for example, '1', not 0x01).

    To enable notifications for this tracker type, enable the session_track_state_change system variable.

    This tracker reports changes for these attributes of session state:

    • The default schema (database).

    • Session-specific values for system variables.

    • User-defined variables.

    • Temporary tables.

    • Prepared statements.

  • SESSION_TRACK_GTIDS: This tracker type indicates that GTIDs are available. data contains the GTID string. length is the string length. The GTID string is in the standard format for specifying a set of GTID values; see GTID Sets.

    To enable notifications for this tracker type, set the session_track_gtids system variable.

  • SESSION_TRACK_TRANSACTION_CHARACTERISTICS: This tracker type indicates that transaction characteristics are available. data is a string containing the characteristics data. length is the string length. The characteristics tracker data string may be empty, or it may contain one or more SQL statements, each terminated by a semicolon:

    • If no characteristics apply, the string is empty. The session defaults apply. (For isolation level and access mode, these defaults are given by the session values of the transaction_isolation and transaction_read_only system variables.)

    • If a transaction was explicitly started, the string contains the statement or statements required to restart the transaction with the same characteristics. As a general rule, this is a START TRANSACTION statement (possibly with one or more of READ ONLY, READ WRITE, and WITH CONSISTENT SNAPSHOT). If any characteristics apply that cannot be passed to START TRANSACTION, such as ISOLATION LEVEL, a suitable SET TRANSACTION statement is prepended (for example, SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION READ WRITE;).

    • If a transaction was not explicitly started, but one-shot characteristics that apply only to the next transaction were set up, a SET TRANSACTION statement suitable for replicating that setup is generated (for example, SET TRANSACTION READ ONLY;).

      Next-transaction characteristics can be set using SET TRANSACTION without any GLOBAL or SESSION keyword, or by setting the transaction_isolation and transaction_read_only system variables using the syntax that applies only to the next transaction:

      SET @@transaction_isolation = value;
      SET @@transaction_read_only = value;
      

      For more information about transaction characteristic scope levels and how they are set, see Transaction Characteristic Scope.

    To enable notifications for this tracker type, set the session_track_transaction_info system variable to CHARACTERISTICS (which also enables the SESSION_TRACK_TRANSACTION_STATE tracker type).

    Transaction characteristics tracking enables the client to determine how to restart a transaction in another session so it has the same characteristics as in the original session.

    Because characteristics may be set using SET TRANSACTION before a transaction is started, it is not safe for the client to assume that there are no transaction characteristics if no transaction is active. It is therefore unsafe not to track transaction characteristics and just switch the connection when no transaction is active (whether this is detected by the transaction state tracker or the traditional SERVER_STATUS_IN_TRANS flag). A client must subscribe to the transaction characteristics tracker if it may wish to switch its session to another connection at some point and transactions may be used.

    The characteristics tracker tracks changes to the one-shot characteristics that apply only to the next transaction. It does not track changes to the session variables. Therefore, the client additionally must track the transaction_isolation and transaction_read_only system variables to correctly determine the session defaults that apply when next-transaction characteristic values are empty. (To track these variables, list them in the value of the session_track_system_variables system variable.)

  • SESSION_TRACK_TRANSACTION_STATE: This tracker type indicates that transaction state information is available. data is a string containing ASCII characters, each of which indicates some aspect of the transaction state. length is the string length (always 8).

    To enable notifications for this tracker type, set the session_track_transaction_info system variable to STATE.

    Transaction state tracking enables the client to determine whether a transaction is in progress and whether it could be moved to a different session without being rolled back.

    The scope of the tracker item is the transaction. All state-indicating flags persist until the transaction is committed or rolled back. As statements are added to the transaction, additional flags may be set in successive tracker data values. However, no flags are cleared until the transaction ends.

    Transaction state is reported as a string containing a sequence of ASCII characters. Each active state has a unique character assigned to it as well as a fixed position in the sequence. The following list describes the permitted values for positions 1 through 8 of the sequence:

    • Position 1: Whether an active transaction is ongoing.

      • T: An explicitly started transaction is ongoing.

      • I: An implicitly started transaction (autocommit=0) is ongoing.

      • _: There is no active transaction.

    • Position 2: Whether nontransactional tables were read in the context of the current transaction.

      • r: One or more nontransactional tables were read.

      • _: No nontransactional tables were read so far.

    • Position 3: Whether transactional tables were read in the context of the current transaction.

      • R: One or more transactional tables were read.

      • _: No transactional tables were read so far.

    • Position 4: Whether unsafe writes (writes to nontransactional tables) were performed in the context of the current transaction.

      • w: One or more nontransactional tables were written.

      • _: No nontransactional tables were written so far.

    • Position 5: Whether any transactional tables were written in the context of the current transaction.

      • W: One or more transactional tables were written.

      • _: No transactional tables were written so far.

    • Position 6: Whether any unsafe statements were executed in the context of the current transaction. Statements containing nondeterministic constructs such as RAND() or UUID() are unsafe for statement-based replication.

      • s: One or more unsafe statements were executed.

      • _: No unsafe statements were executed so far.

    • Position 7: Whether a result set was sent to the client during the current transaction.

      • S: A result set was sent.

      • _: No result sets were sent so far.

    • Position 8: Whether a LOCK TABLES statement is in effect.

    Consider a session consisting of the following statements, including one to enable the transaction state tracker:

    1. SET @@SESSION.session_track_transaction_info='STATE';
    2. START TRANSACTION;
    3. SELECT 1;
    4. INSERT INTO t1 () VALUES();
    5. INSERT INTO t1 () VALUES(1, RAND());
    6. COMMIT;

    With transaction state tracking enabled, the following data values result from those statements:

    1. ________
    2. T_______
    3. T_____S_
    4. T___W_S_
    5. T___WsS_
    6. ________
Return Values

Zero for success. Nonzero if an error occurred.

Errors

None.

Example

The following example shows how to call mysql_session_track_get_first() and mysql_session_track_get_next() to retrieve and display all available session state-change information following successful execution of an SQL statement string (represented by stmt_str). It is assumed that the application has set the session_track_xxx system variables that enable the notifications it wishes to receive.

printf("Execute: %s\n", stmt_str);

if (mysql_query(mysql, stmt_str) != 0)
{
  fprintf(stderr, "Error %u: %s\n",
           mysql_errno(mysql), mysql_error(mysql));
  return;
}

MYSQL_RES *result = mysql_store_result(mysql);
if (result) /* there is a result set to fetch */
{
  /* ... process rows here ... */
  printf("Number of rows returned: %lu\n",
          (unsigned long) mysql_num_rows(result));
  mysql_free_result(result);
}
else        /* there is no result set */
{
  if (mysql_field_count(mysql) == 0)
  {
    printf("Number of rows affected: %lu\n",
            (unsigned long) mysql_affected_rows(mysql));
  }
  else      /* an error occurred */
  {
    fprintf(stderr, "Error %u: %s\n",
             mysql_errno(mysql), mysql_error(mysql));
  }
}

/* extract any available session state-change information */
enum enum_session_state_type type;
for (type = SESSION_TRACK_BEGIN; type <= SESSION_TRACK_END; type++)
{
  const char *data;
  size_t length;

  if (mysql_session_track_get_first(mysql, type, &data, &length) == 0)
  {
    /* print info type and initial data */
    printf("Type=%d:\n", type);
    printf("mysql_session_track_get_first(): length=%d; data=%*.*s\n",
           (int) length, (int) length, (int) length, data);

    /* check for more data */
    while (mysql_session_track_get_next(mysql, type, &data, &length) == 0)
    {
      printf("mysql_session_track_get_next(): length=%d; data=%*.*s\n",
             (int) length, (int) length, (int) length, data);
    }
  }
}

27.7.6.66 mysql_session_track_get_next()

int mysql_session_track_get_next(MYSQL *mysql, enum enum_session_state_type type, const char **data, size_t *length)

Description

This function fetches additional session state-change information received from the server, following that retrieved by mysql_session_track_get_first(). The parameters for mysql_session_track_get_next() are the same as for mysql_session_track_get_first().

Following a successful call to mysql_session_track_get_first(), call mysql_session_track_get_next() repeatedly until it returns nonzero to indicate no more information is available. The calling sequence for mysql_session_track_get_next() is similar to that for mysql_session_track_get_first(). For more information and an example that demonstrates both functions, see Section 27.7.6.65, “mysql_session_track_get_first()”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

None.

27.7.6.67 mysql_set_character_set()

int mysql_set_character_set(MYSQL *mysql, const char *csname)

Description

This function is used to set the default character set for the current connection. The string csname specifies a valid character set name. The connection collation becomes the default collation of the character set. This function works like the SET NAMES statement, but also sets the value of mysql->charset, and thus affects the character set used by mysql_real_escape_string()

Return Values

Zero for success. Nonzero if an error occurred.

Example
MYSQL mysql;

mysql_init(&mysql);
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

if (!mysql_set_character_set(&mysql, "utf8"))
{
    printf("New client character set: %s\n",
           mysql_character_set_name(&mysql));
}

27.7.6.68 mysql_set_local_infile_default()

void mysql_set_local_infile_default(MYSQL *mysql);

Description

Sets the LOAD DATA LOCAL callback functions to the defaults used internally by the C client library. The library calls this function automatically if mysql_set_local_infile_handler() has not been called or does not supply valid functions for each of its callbacks.

Return Values

None.

Errors

None.

27.7.6.69 mysql_set_local_infile_handler()

void mysql_set_local_infile_handler(MYSQL *mysql, int (*local_infile_init)(void **, const char *, void *), int (*local_infile_read)(void *, char *, unsigned int), void (*local_infile_end)(void *), int (*local_infile_error)(void *, char*, unsigned int), void *userdata);

Description

This function installs callbacks to be used during the execution of LOAD DATA LOCAL statements. It enables application programs to exert control over local (client-side) data file reading. The arguments are the connection handler, a set of pointers to callback functions, and a pointer to a data area that the callbacks can use to share information.

To use mysql_set_local_infile_handler(), you must write the following callback functions:

int
local_infile_init(void **ptr, const char *filename, void *userdata);

The initialization function. This is called once to do any setup necessary, open the data file, allocate data structures, and so forth. The first void** argument is a pointer to a pointer. You can set the pointer (that is, *ptr) to a value that will be passed to each of the other callbacks (as a void*). The callbacks can use this pointed-to value to maintain state information. The userdata argument is the same value that is passed to mysql_set_local_infile_handler().

Make the initialization function return zero for success, nonzero for an error.

int
local_infile_read(void *ptr, char *buf, unsigned int buf_len);

The data-reading function. This is called repeatedly to read the data file. buf points to the buffer where the read data is stored, and buf_len is the maximum number of bytes that the callback can read and store in the buffer. (It can read fewer bytes, but should not read more.)

The return value is the number of bytes read, or zero when no more data could be read (this indicates EOF). Return a value less than zero if an error occurs.

void
local_infile_end(void *ptr)

The termination function. This is called once after local_infile_read() has returned zero (EOF) or an error. Within this function, deallocate any memory allocated by local_infile_init() and perform any other cleanup necessary. It is invoked even if the initialization function returns an error.

int
local_infile_error(void *ptr,
                   char *error_msg,
                   unsigned int error_msg_len);

The error-handling function. This is called to get a textual error message to return to the user in case any of your other functions returns an error. error_msg points to the buffer into which the message is written, and error_msg_len is the length of the buffer. Write the message as a null-terminated string, at most error_msg_len−1 bytes long.

The return value is the error number.

Typically, the other callbacks store the error message in the data structure pointed to by ptr, so that local_infile_error() can copy the message from there into error_msg.

After calling mysql_set_local_infile_handler() in your C code and passing pointers to your callback functions, you can then issue a LOAD DATA LOCAL statement (for example, by using mysql_query()). The client library automatically invokes your callbacks. The file name specified in LOAD DATA LOCAL will be passed as the second parameter to the local_infile_init() callback.

Return Values

None.

Errors

None.

27.7.6.70 mysql_set_server_option()

int mysql_set_server_option(MYSQL *mysql, enum enum_mysql_set_option option)

Description

Enables or disables an option for the connection. option can have one of the following values.

Option Description
MYSQL_OPTION_MULTI_STATEMENTS_ON Enable multiple-statement support
MYSQL_OPTION_MULTI_STATEMENTS_OFF Disable multiple-statement support

If you enable multiple-statement support, you should retrieve results from calls to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 27.7.15, “C API Multiple Statement Execution Support”.

Enabling multiple-statement support with MYSQL_OPTION_MULTI_STATEMENTS_ON does not have quite the same effect as enabling it by passing the CLIENT_MULTI_STATEMENTS flag to mysql_real_connect(): CLIENT_MULTI_STATEMENTS also enables CLIENT_MULTI_RESULTS. If you are using the CALL SQL statement in your programs, multiple-result support must be enabled; this means that MYSQL_OPTION_MULTI_STATEMENTS_ON by itself is insufficient to permit the use of CALL.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.71 mysql_shutdown()

int mysql_shutdown(MYSQL *mysql, enum mysql_enum_shutdown_level shutdown_level)

Description
Note

mysql_shutdown() is deprecated and will be removed in a future version of MySQL. Instead, use mysql_query() to execute a SHUTDOWN statement.

Asks the database server to shut down. The connected user must have the SHUTDOWN privilege. MySQL servers support only one type of shutdown; shutdown_level must be equal to SHUTDOWN_DEFAULT. Dynamically linked executables that have been compiled with older versions of the libmysqlclient headers and call mysql_shutdown() must be used with the old libmysqlclient dynamic library.

An alternative to mysql_shutdown() is to use the SHUTDOWN SQL statement.

The shutdown process is described in Section 5.1.15, “The Server Shutdown Process”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.6.72 mysql_sqlstate()

const char *mysql_sqlstate(MYSQL *mysql)

Description

Returns a null-terminated string containing the SQLSTATE error code for the most recently executed SQL statement. The error code consists of five characters. '00000' means no error. The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix B, Errors, Error Codes, and Common Problems.

SQLSTATE values returned by mysql_sqlstate() differ from MySQL-specific error numbers returned by mysql_errno(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist

Not all MySQL error numbers are mapped to SQLSTATE error codes. The value 'HY000' (general error) is used for unmapped error numbers.

If you call mysql_sqlstate() after mysql_real_connect() fails, mysql_sqlstate() might not return a useful value. For example, this happens if a host is blocked by the server and the connection is closed without any SQLSTATE value being sent to the client.

Return Values

A null-terminated character string containing the SQLSTATE error code.

27.7.6.73 mysql_ssl_set()

my_bool mysql_ssl_set(MYSQL *mysql, const char *key, const char *cert, const char *ca, const char *capath, const char *cipher)

Description

mysql_ssl_set() is used for establishing encrypted connections using SSL. The mysql argument must be a valid connection handler. Any unused SSL arguments may be given as NULL.

If used, mysql_ssl_set() must be called before mysql_real_connect(). mysql_ssl_set() does nothing unless SSL support is enabled in the client library.

It is optional to call mysql_ssl_set() to obtain an encrypted connection because by default, MySQL programs attempt to connect using encryption if the server supports encrypted connections, falling back to an unencrypted connection if an encrypted connection cannot be established (see Section 6.3.1, “Configuring MySQL to Use Encrypted Connections”). mysql_ssl_set() may be useful to applications that must specify particular certificate and key files, encryption ciphers, and so forth.

mysql_ssl_set() specifies SSL information such as certificate and key files for establishing an encrypted connection if such connections are available, but does not enforce any requirement that the connection obtained be encrypted. To require an encrypted connection, use the technique described in Section 27.7.14, “C API Encrypted Connection Support”.

For additional security relative to that provided by the default encryption, clients can supply a CA certificate matching the one used by the server and enable host name identity verification. In this way, the server and client place their trust in the same CA certificate and the client verifies that the host to which it connected is the one intended. For details, see Section 27.7.14, “C API Encrypted Connection Support”.

mysql_ssl_set() is a convenience function that is essentially equivalent to this set of mysql_options() calls:

mysql_options(mysql, MYSQL_OPT_SSL_KEY,    key);
mysql_options(mysql, MYSQL_OPT_SSL_CERT,   cert);
mysql_options(mysql, MYSQL_OPT_SSL_CA,     ca);
mysql_options(mysql, MYSQL_OPT_SSL_CAPATH, capath);
mysql_options(mysql, MYSQL_OPT_SSL_CIPHER, cipher);

Because of that equivalence, applications can, instead of calling mysql_ssl_set(), call mysql_options() directly, omitting calls for those options for which the option value is NULL. Moreover, mysql_options() offers encrypted-connection options not available using mysql_ssl_set(), such as MYSQL_OPT_SSL_MODE to specify the security state of the connection, and MYSQL_OPT_TLS_VERSION to specify the protocols the client permits for encrypted connections.

Arguments:

  • mysql: The connection handler returned from mysql_init().

  • key: The path name of the client private key file.

  • cert: The path name of the client public key certificate file.

  • ca: The path name of the Certificate Authority (CA) certificate file. This option, if used, must specify the same certificate used by the server.

  • capath: The path name of the directory that contains trusted SSL CA certificate files.

  • cipher: The list of permissible ciphers for SSL encryption.

Return Values

This function always returns 0. If SSL setup is incorrect, a subsequent mysql_real_connect() call returns an error when you attempt to connect.

27.7.6.74 mysql_stat()

const char *mysql_stat(MYSQL *mysql)

Description

Returns a character string containing information similar to that provided by the mysqladmin status command. This includes uptime in seconds and the number of running threads, questions, reloads, and open tables.

Return Values

A character string describing the server status. NULL if an error occurred.

Errors

27.7.6.75 mysql_store_result()

MYSQL_RES *mysql_store_result(MYSQL *mysql)

Description

After invoking mysql_query() or mysql_real_query(), you must call mysql_store_result() or mysql_use_result() for every statement that successfully produces a result set (SELECT, SHOW, DESCRIBE, EXPLAIN, CHECK TABLE, and so forth). You must also call mysql_free_result() after you are done with the result set.

You need not call mysql_store_result() or mysql_use_result() for other statements, but it does not do any harm or cause any notable performance degradation if you call mysql_store_result() in all cases. You can detect whether the statement has a result set by checking whether mysql_store_result() returns a nonzero value (more about this later).

If you enable multiple-statement support, you should retrieve results from calls to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 27.7.15, “C API Multiple Statement Execution Support”.

If you want to know whether a statement should return a result set, you can use mysql_field_count() to check for this. See Section 27.7.6.22, “mysql_field_count()”.

mysql_store_result() reads the entire result of a query to the client, allocates a MYSQL_RES structure, and places the result into this structure.

mysql_store_result() returns NULL if the statement did not return a result set (for example, if it was an INSERT statement), or an error occurred and reading of the result set failed.

An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)

After you have called mysql_store_result() and gotten back a result that is not a null pointer, you can call mysql_num_rows() to find out how many rows are in the result set.

You can call mysql_fetch_row() to fetch rows from the result set, or mysql_row_seek() and mysql_row_tell() to obtain or set the current row position within the result set.

See Section 27.7.20.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

A pointer to a MYSQL_RES result structure with the results. NULL if the statement did not return a result set or an error occurred. To determine whether an error occurred, check whether mysql_error() returns a nonempty string, mysql_errno() returns nonzero, or mysql_field_count() returns zero.

Errors

mysql_store_result() resets mysql_error() and mysql_errno() if it succeeds.

27.7.6.76 mysql_thread_id()

unsigned long mysql_thread_id(MYSQL *mysql)

Description

Returns the thread ID of the current connection. This value can be used as an argument to mysql_kill() to kill the thread.

If the connection is lost and you reconnect with mysql_ping(), the thread ID changes. This means you should not get the thread ID and store it for later. You should get it when you need it.

Note

This function does not work correctly if thread IDs become larger than 32 bits, which can occur on some systems. To avoid problems with mysql_thread_id(), do not use it. To get the connection ID, execute a SELECT CONNECTION_ID() query and retrieve the result.

Return Values

The thread ID of the current connection.

Errors

None.

27.7.6.77 mysql_use_result()

MYSQL_RES *mysql_use_result(MYSQL *mysql)

Description

After invoking mysql_query() or mysql_real_query(), you must call mysql_store_result() or mysql_use_result() for every statement that successfully produces a result set (SELECT, SHOW, DESCRIBE, EXPLAIN, CHECK TABLE, and so forth). You must also call mysql_free_result() after you are done with the result set.

mysql_use_result() initiates a result set retrieval but does not actually read the result set into the client like mysql_store_result() does. Instead, each row must be retrieved individually by making calls to mysql_fetch_row(). This reads the result of a query directly from the server without storing it in a temporary table or local buffer, which is somewhat faster and uses much less memory than mysql_store_result(). The client allocates memory only for the current row and a communication buffer that may grow up to max_allowed_packet bytes.

On the other hand, you should not use mysql_use_result() for locking reads if you are doing a lot of processing for each row on the client side, or if the output is sent to a screen on which the user may type a ^S (stop scroll). This ties up the server and prevent other threads from updating any tables from which the data is being fetched.

When using mysql_use_result(), you must execute mysql_fetch_row() until a NULL value is returned, otherwise, the unfetched rows are returned as part of the result set for your next query. The C API gives the error Commands out of sync; you can't run this command now if you forget to do this!

You may not use mysql_data_seek(), mysql_row_seek(), mysql_row_tell(), mysql_num_rows(), or mysql_affected_rows() with a result returned from mysql_use_result(), nor may you issue other queries until mysql_use_result() has finished. (However, after you have fetched all the rows, mysql_num_rows() accurately returns the number of rows fetched.)

You must call mysql_free_result() once you are done with the result set.

When using the libmysqld embedded server, the memory benefits are essentially lost because memory usage incrementally increases with each row retrieved until mysql_free_result() is called.

Return Values

A MYSQL_RES result structure. NULL if an error occurred.

Errors

mysql_use_result() resets mysql_error() and mysql_errno() if it succeeds.

27.7.6.78 mysql_warning_count()

unsigned int mysql_warning_count(MYSQL *mysql)

Description

Returns the number of errors, warnings, and notes generated during execution of the previous SQL statement.

Return Values

The warning count.

Errors

None.

27.7.7 C API Prepared Statements

The MySQL client/server protocol provides for the use of prepared statements. This capability uses the MYSQL_STMT statement handler data structure returned by the mysql_stmt_init() initialization function. Prepared execution is an efficient way to execute a statement more than once. The statement is first parsed to prepare it for execution. Then it is executed one or more times at a later time, using the statement handler returned by the initialization function.

Prepared execution is faster than direct execution for statements executed more than once, primarily because the query is parsed only once. In the case of direct execution, the query is parsed every time it is executed. Prepared execution also can provide a reduction of network traffic because for each execution of the prepared statement, it is necessary only to send the data for the parameters.

Prepared statements might not provide a performance increase in some situations. For best results, test your application both with prepared and nonprepared statements and choose whichever yields best performance.

Another advantage of prepared statements is that it uses a binary protocol that makes data transfer between client and server more efficient.

For a list of SQL statements that can be used as prepared statements, see Section 13.5, “Prepared Statements”.

Metadata changes to tables or views referred to by prepared statements are detected and cause automatic repreparation of the statement when it is next executed. For more information, see Section 8.10.4, “Caching of Prepared Statements and Stored Programs”.

27.7.8 C API Prepared Statement Data Structures

Prepared statements use several data structures:

  • To obtain a statement handler, pass a MYSQL connection handler to mysql_stmt_init(), which returns a pointer to a MYSQL_STMT data structure. This structure is used for further operations with the statement. To specify the statement to prepare, pass the MYSQL_STMT pointer and the statement string to mysql_stmt_prepare().

  • To provide input parameters for a prepared statement, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_param(). To receive output column values, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_result().

  • The MYSQL_TIME structure is used to transfer temporal data in both directions.

The following discussion describes the prepared statement data types in detail. For examples that show how to use them, see Section 27.7.10.10, “mysql_stmt_execute()”, and Section 27.7.10.11, “mysql_stmt_fetch()”.

  • MYSQL_STMT

    This structure is a handler for a prepared statement. A handler is created by calling mysql_stmt_init(), which returns a pointer to a MYSQL_STMT. The handler is used for all subsequent operations with the statement until you close it with mysql_stmt_close(), at which point the handler becomes invalid and should no longer be used.

    The MYSQL_STMT structure has no members intended for application use. Applications should not try to copy a MYSQL_STMT structure. There is no guarantee that such a copy will be usable.

    Multiple statement handlers can be associated with a single connection. The limit on the number of handlers depends on the available system resources.

  • MYSQL_BIND

    This structure is used both for statement input (data values sent to the server) and output (result values returned from the server):

    To use a MYSQL_BIND structure, zero its contents to initialize it, then set its members appropriately. For example, to declare and initialize an array of three MYSQL_BIND structures, use this code:

    MYSQL_BIND bind[3];
    memset(bind, 0, sizeof(bind));

    The MYSQL_BIND structure contains the following members for use by application programs. For several of the members, the manner of use depends on whether the structure is used for input or output.

    • enum enum_field_types buffer_type

      The type of the buffer. This member indicates the data type of the C language variable bound to a statement parameter or result set column. For input, buffer_type indicates the type of the variable containing the value to be sent to the server. For output, it indicates the type of the variable into which a value received from the server should be stored. For permissible buffer_type values, see Section 27.7.8.1, “C API Prepared Statement Type Codes”.

    • void *buffer

      A pointer to the buffer to be used for data transfer. This is the address of a C language variable.

      For input, buffer is a pointer to the variable in which you store the data value for a statement parameter. When you call mysql_stmt_execute(), MySQL use the value stored in the variable in place of the corresponding parameter marker in the statement (specified with ? in the statement string).

      For output, buffer is a pointer to the variable in which to return a result set column value. When you call mysql_stmt_fetch(), MySQL stores a column value from the current row of the result set in this variable. You can access the value when the call returns.

      To minimize the need for MySQL to perform type conversions between C language values on the client side and SQL values on the server side, use C variables that have types similar to those of the corresponding SQL values:

      • For numeric data types, buffer should point to a variable of the proper numeric C type. For integer variables (which can be char for single-byte values or an integer type for larger values), you should also indicate whether the variable has the unsigned attribute by setting the is_unsigned member, described later.

      • For character (nonbinary) and binary string data types, buffer should point to a character buffer.

      • For date and time data types, buffer should point to a MYSQL_TIME structure.

      For guidelines about mapping between C types and SQL types and notes about type conversions, see Section 27.7.8.1, “C API Prepared Statement Type Codes”, and Section 27.7.8.2, “C API Prepared Statement Type Conversions”.

    • unsigned long buffer_length

      The actual size of *buffer in bytes. This indicates the maximum amount of data that can be stored in the buffer. For character and binary C data, the buffer_length value specifies the length of *buffer when used with mysql_stmt_bind_param() to specify input values, or the maximum number of output data bytes that can be fetched into the buffer when used with mysql_stmt_bind_result().

    • unsigned long *length

      A pointer to an unsigned long variable that indicates the actual number of bytes of data stored in *buffer. length is used for character or binary C data.

      For input parameter data binding, set *length to indicate the actual length of the parameter value stored in *buffer. This is used by mysql_stmt_execute().

      For output value binding, MySQL sets *length when you call mysql_stmt_fetch(). The mysql_stmt_fetch() return value determines how to interpret the length:

      • If the return value is 0, *length indicates the actual length of the parameter value.

      • If the return value is MYSQL_DATA_TRUNCATED, *length indicates the nontruncated length of the parameter value. In this case, the minimum of *length and buffer_length indicates the actual length of the value.

      length is ignored for numeric and temporal data types because the buffer_type value determines the length of the data value.

      If you must determine the length of a returned value before fetching it, see Section 27.7.10.11, “mysql_stmt_fetch()”, for some strategies.

    • my_bool *is_null

      This member points to a my_bool variable that is true if a value is NULL, false if it is not NULL. For input, set *is_null to true to indicate that you are passing a NULL value as a statement parameter.

      is_null is a pointer to a boolean scalar, not a boolean scalar, to provide flexibility in how you specify NULL values:

      • If your data values are always NULL, use MYSQL_TYPE_NULL as the buffer_type value when you bind the column. The other MYSQL_BIND members, including is_null, do not matter.

      • If your data values are always NOT NULL, set is_null = (my_bool*) 0, and set the other members appropriately for the variable you are binding.

      • In all other cases, set the other members appropriately and set is_null to the address of a my_bool variable. Set that variable's value to true or false appropriately between executions to indicate whether the corresponding data value is NULL or NOT NULL, respectively.

      For output, when you fetch a row, MySQL sets the value pointed to by is_null to true or false according to whether the result set column value returned from the statement is or is not NULL.

    • my_bool is_unsigned

      This member applies for C variables with data types that can be unsigned (char, short int, int, long long int). Set is_unsigned to true if the variable pointed to by buffer is unsigned and false otherwise. For example, if you bind a signed char variable to buffer, specify a type code of MYSQL_TYPE_TINY and set is_unsigned to false. If you bind an unsigned char instead, the type code is the same but is_unsigned should be true. (For char, it is not defined whether it is signed or unsigned, so it is best to be explicit about signedness by using signed char or unsigned char.)

      is_unsigned applies only to the C language variable on the client side. It indicates nothing about the signedness of the corresponding SQL value on the server side. For example, if you use an int variable to supply a value for a BIGINT UNSIGNED column, is_unsigned should be false because int is a signed type. If you use an unsigned int variable to supply a value for a BIGINT column, is_unsigned should be true because unsigned int is an unsigned type. MySQL performs the proper conversion between signed and unsigned values in both directions, although a warning occurs if truncation results.

    • my_bool *error

      For output, set this member to point to a my_bool variable to have truncation information for the parameter stored there after a row fetching operation. When truncation reporting is enabled, mysql_stmt_fetch() returns MYSQL_DATA_TRUNCATED and *error is true in the MYSQL_BIND structures for parameters in which truncation occurred. Truncation indicates loss of sign or significant digits, or that a string was too long to fit in a column. Truncation reporting is enabled by default, but can be controlled by calling mysql_options() with the MYSQL_REPORT_DATA_TRUNCATION option.

  • MYSQL_TIME

    This structure is used to send and receive DATE, TIME, DATETIME, and TIMESTAMP data directly to and from the server. Set the buffer member to point to a MYSQL_TIME structure, and set the buffer_type member of a MYSQL_BIND structure to one of the temporal types (MYSQL_TYPE_TIME, MYSQL_TYPE_DATE, MYSQL_TYPE_DATETIME, MYSQL_TYPE_TIMESTAMP).

    The MYSQL_TIME structure contains the members listed in the following table.

    Member Description
    unsigned int year The year
    unsigned int month The month of the year
    unsigned int day The day of the month
    unsigned int hour The hour of the day
    unsigned int minute The minute of the hour
    unsigned int second The second of the minute
    my_bool neg A boolean flag indicating whether the time is negative
    unsigned long second_part The fractional part of the second in microseconds

    Only those parts of a MYSQL_TIME structure that apply to a given type of temporal value are used. The year, month, and day elements are used for DATE, DATETIME, and TIMESTAMP values. The hour, minute, and second elements are used for TIME, DATETIME, and TIMESTAMP values. See Section 27.7.16, “C API Prepared Statement Handling of Date and Time Values”.

27.7.8.1 C API Prepared Statement Type Codes

The buffer_type member of MYSQL_BIND structures indicates the data type of the C language variable bound to a statement parameter or result set column. For input, buffer_type indicates the type of the variable containing the value to be sent to the server. For output, it indicates the type of the variable into which a value received from the server should be stored.

The following table shows the permissible values for the buffer_type member of MYSQL_BIND structures for input values sent to the server. The table shows the C variable types that you can use, the corresponding type codes, and the SQL data types for which the supplied value can be used without conversion. Choose the buffer_type value according to the data type of the C language variable that you are binding. For the integer types, you should also set the is_unsigned member to indicate whether the variable is signed or unsigned.

Input Variable C Type buffer_type Value SQL Type of Destination Value
signed char MYSQL_TYPE_TINY TINYINT
short int MYSQL_TYPE_SHORT SMALLINT
int MYSQL_TYPE_LONG INT
long long int MYSQL_TYPE_LONGLONG BIGINT
float MYSQL_TYPE_FLOAT FLOAT
double MYSQL_TYPE_DOUBLE DOUBLE
MYSQL_TIME MYSQL_TYPE_TIME TIME
MYSQL_TIME MYSQL_TYPE_DATE DATE
MYSQL_TIME MYSQL_TYPE_DATETIME DATETIME
MYSQL_TIME MYSQL_TYPE_TIMESTAMP TIMESTAMP
char[] MYSQL_TYPE_STRING TEXT, CHAR, VARCHAR
char[] MYSQL_TYPE_BLOB BLOB, BINARY, VARBINARY
MYSQL_TYPE_NULL NULL

Use MYSQL_TYPE_NULL as indicated in the description for the is_null member in Section 27.7.8, “C API Prepared Statement Data Structures”.

For input string data, use MYSQL_TYPE_STRING or MYSQL_TYPE_BLOB depending on whether the value is a character (nonbinary) or binary string:

  • MYSQL_TYPE_STRING indicates character input string data. The value is assumed to be in the character set indicated by the character_set_client system variable. If the server stores the value into a column with a different character set, it converts the value to that character set.

  • MYSQL_TYPE_BLOB indicates binary input string data. The value is treated as having the binary character set. That is, it is treated as a byte string and no conversion occurs.

The following table shows the permissible values for the buffer_type member of MYSQL_BIND structures for output values received from the server. The table shows the SQL types of received values, the corresponding type codes that such values have in result set metadata, and the recommended C language data types to bind to the MYSQL_BIND structure to receive the SQL values without conversion. Choose the buffer_type value according to the data type of the C language variable that you are binding. For the integer types, you should also set the is_unsigned member to indicate whether the variable is signed or unsigned.

SQL Type of Received Value buffer_type Value Output Variable C Type
TINYINT MYSQL_TYPE_TINY signed char
SMALLINT MYSQL_TYPE_SHORT short int
MEDIUMINT MYSQL_TYPE_INT24 int
INT MYSQL_TYPE_LONG int
BIGINT MYSQL_TYPE_LONGLONG long long int
FLOAT MYSQL_TYPE_FLOAT float
DOUBLE MYSQL_TYPE_DOUBLE double
DECIMAL MYSQL_TYPE_NEWDECIMAL char[]
YEAR MYSQL_TYPE_SHORT short int
TIME MYSQL_TYPE_TIME MYSQL_TIME
DATE MYSQL_TYPE_DATE MYSQL_TIME
DATETIME MYSQL_TYPE_DATETIME MYSQL_TIME
TIMESTAMP MYSQL_TYPE_TIMESTAMP MYSQL_TIME
CHAR, BINARY MYSQL_TYPE_STRING char[]
VARCHAR, VARBINARY MYSQL_TYPE_VAR_STRING char[]
TINYBLOB, TINYTEXT MYSQL_TYPE_TINY_BLOB char[]
BLOB, TEXT MYSQL_TYPE_BLOB char[]
MEDIUMBLOB, MEDIUMTEXT MYSQL_TYPE_MEDIUM_BLOB char[]
LONGBLOB, LONGTEXT MYSQL_TYPE_LONG_BLOB char[]
BIT MYSQL_TYPE_BIT char[]

27.7.8.2 C API Prepared Statement Type Conversions

Prepared statements transmit data between the client and server using C language variables on the client side that correspond to SQL values on the server side. If there is a mismatch between the C variable type on the client side and the corresponding SQL value type on the server side, MySQL performs implicit type conversions in both directions.

MySQL knows the type code for the SQL value on the server side. The buffer_type value in the MYSQL_BIND structure indicates the type code of the C variable that holds the value on the client side. The two codes together tell MySQL what conversion must be performed, if any. Here are some examples:

  • If you use MYSQL_TYPE_LONG with an int variable to pass an integer value to the server that is to be stored into a FLOAT column, MySQL converts the value to floating-point format before storing it.

  • If you fetch an SQL MEDIUMINT column value, but specify a buffer_type value of MYSQL_TYPE_LONGLONG and use a C variable of type long long int as the destination buffer, MySQL converts the MEDIUMINT value (which requires less than 8 bytes) for storage into the long long int (an 8-byte variable).

  • If you fetch a numeric column with a value of 255 into a char[4] character array and specify a buffer_type value of MYSQL_TYPE_STRING, the resulting value in the array is a 4-byte string '255\0'.

  • MySQL returns DECIMAL values as the string representation of the original server-side value, which is why the corresponding C type is char[]. For example, 12.345 is returned to the client as '12.345'. If you specify MYSQL_TYPE_NEWDECIMAL and bind a string buffer to the MYSQL_BIND structure, mysql_stmt_fetch() stores the value in the buffer as a string without conversion. If instead you specify a numeric variable and type code, mysql_stmt_fetch() converts the string-format DECIMAL value to numeric form.

  • For the MYSQL_TYPE_BIT type code, BIT values are returned into a string buffer, which is why the corresponding C type is char[]. The value represents a bit string that requires interpretation on the client side. To return the value as a type that is easier to deal with, you can cause the value to be cast to integer using either of the following types of expressions:

    SELECT bit_col + 0 FROM t
    SELECT CAST(bit_col AS UNSIGNED) FROM t

    To retrieve the value, bind an integer variable large enough to hold the value and specify the appropriate corresponding integer type code.

Before binding variables to the MYSQL_BIND structures that are to be used for fetching column values, you can check the type codes for each column of the result set. This might be desirable if you want to determine which variable types would be best to use to avoid type conversions. To get the type codes, call mysql_stmt_result_metadata() after executing the prepared statement with mysql_stmt_execute(). The metadata provides access to the type codes for the result set as described in Section 27.7.10.23, “mysql_stmt_result_metadata()”, and Section 27.7.4, “C API Data Structures”.

To determine whether output string values in a result set returned from the server contain binary or nonbinary data, check whether the charsetnr value of the result set metadata is 63 (see Section 27.7.4, “C API Data Structures”). If so, the character set is binary, which indicates binary rather than nonbinary data. This enables you to distinguish BINARY from CHAR, VARBINARY from VARCHAR, and the BLOB types from the TEXT types.

If you cause the max_length member of the MYSQL_FIELD column metadata structures to be set (by calling mysql_stmt_attr_set()), be aware that the max_length values for the result set indicate the lengths of the longest string representation of the result values, not the lengths of the binary representation. That is, max_length does not necessarily correspond to the size of the buffers needed to fetch the values with the binary protocol used for prepared statements. Choose the size of the buffers according to the types of the variables into which you fetch the values. For example, a TINYINT column containing the value -128 might have a max_length value of 4. But the binary representation of any TINYINT value requires only 1 byte for storage, so you can supply a signed char variable in which to store the value and set is_unsigned to indicate that values are signed.

Metadata changes to tables or views referred to by prepared statements are detected and cause automatic repreparation of the statement when it is next executed. For more information, see Section 8.10.4, “Caching of Prepared Statements and Stored Programs”.

27.7.9 C API Prepared Statement Function Overview

The following list summarizes the functions available for prepared statement processing. For greater detail, see the descriptions in Section 27.7.10, “C API Prepared Statement Function Descriptions”.

Call mysql_stmt_init() to create a statement handler, then mysql_stmt_prepare() to prepare the statement string, mysql_stmt_bind_param() to supply the parameter data, and mysql_stmt_execute() to execute the statement. You can repeat the mysql_stmt_execute() by changing parameter values in the respective buffers supplied through mysql_stmt_bind_param().

You can send text or binary data in chunks to server using mysql_stmt_send_long_data(). See Section 27.7.10.26, “mysql_stmt_send_long_data()”.

If the statement is a SELECT or any other statement that produces a result set, mysql_stmt_prepare() also returns the result set metadata information in the form of a MYSQL_RES result set through mysql_stmt_result_metadata().

You can supply the result buffers using mysql_stmt_bind_result(), so that the mysql_stmt_fetch() automatically returns data to these buffers. This is row-by-row fetching.

When statement execution has been completed, close the statement handler using mysql_stmt_close() so that all resources associated with it can be freed. At that point the handler becomes invalid and should no longer be used.

If you obtained a SELECT statement's result set metadata by calling mysql_stmt_result_metadata(), you should also free the metadata using mysql_free_result().

Execution Steps

To prepare and execute a statement, an application follows these steps:

  1. Create a prepared statement handler with mysql_stmt_init(). To prepare the statement on the server, call mysql_stmt_prepare() and pass it a string containing the SQL statement.

  2. If the statement will produce a result set, call mysql_stmt_result_metadata() to obtain the result set metadata. This metadata is itself in the form of result set, albeit a separate one from the one that contains the rows returned by the query. The metadata result set indicates how many columns are in the result and contains information about each column.

  3. Set the values of any parameters using mysql_stmt_bind_param(). All parameters must be set. Otherwise, statement execution returns an error or produces unexpected results.

  4. Call mysql_stmt_execute() to execute the statement.

  5. If the statement produces a result set, bind the data buffers to use for retrieving the row values by calling mysql_stmt_bind_result().

  6. Fetch the data into the buffers row by row by calling mysql_stmt_fetch() repeatedly until no more rows are found.

  7. Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the statement.

When mysql_stmt_prepare() is called, the MySQL client/server protocol performs these actions:

  • The server parses the statement and sends the okay status back to the client by assigning a statement ID. It also sends total number of parameters, a column count, and its metadata if it is a result set oriented statement. All syntax and semantics of the statement are checked by the server during this call.

  • The client uses this statement ID for the further operations, so that the server can identify the statement from among its pool of statements.

When mysql_stmt_execute() is called, the MySQL client/server protocol performs these actions:

  • The client uses the statement handler and sends the parameter data to the server.

  • The server identifies the statement using the ID provided by the client, replaces the parameter markers with the newly supplied data, and executes the statement. If the statement produces a result set, the server sends the data back to the client. Otherwise, it sends an okay status and the number of rows changed, deleted, or inserted.

When mysql_stmt_fetch() is called, the MySQL client/server protocol performs these actions:

  • The client reads the data from the current row of the result set and places it into the application data buffers by doing the necessary conversions. If the application buffer type is same as that of the field type returned from the server, the conversions are straightforward.

If an error occurs, you can get the statement error number, error message, and SQLSTATE code using mysql_stmt_errno(), mysql_stmt_error(), and mysql_stmt_sqlstate(), respectively.

Prepared Statement Logging

For prepared statements that are executed with the mysql_stmt_prepare() and mysql_stmt_execute() C API functions, the server writes Prepare and Execute lines to the general query log so that you can tell when statements are prepared and executed.

Suppose that you prepare and execute a statement as follows:

  1. Call mysql_stmt_prepare() to prepare the statement string "SELECT ?".

  2. Call mysql_stmt_bind_param() to bind the value 3 to the parameter in the prepared statement.

  3. Call mysql_stmt_execute() to execute the prepared statement.

As a result of the preceding calls, the server writes the following lines to the general query log:

Prepare  [1] SELECT ?
Execute  [1] SELECT 3

Each Prepare and Execute line in the log is tagged with a [N] statement identifier so that you can keep track of which prepared statement is being logged. N is a positive integer. If there are multiple prepared statements active simultaneously for the client, N may be greater than 1. Each Execute lines shows a prepared statement after substitution of data values for ? parameters.

27.7.10 C API Prepared Statement Function Descriptions

To prepare and execute queries, use the functions described in detail in the following sections.

All functions that operate with a MYSQL_STMT structure begin with the prefix mysql_stmt_.

To create a MYSQL_STMT handler, use the mysql_stmt_init() function.

27.7.10.1 mysql_stmt_affected_rows()

my_ulonglong mysql_stmt_affected_rows(MYSQL_STMT *stmt)

Description

mysql_stmt_affected_rows() may be called immediately after executing a statement with mysql_stmt_execute(). It is like mysql_affected_rows() but for prepared statements. For a description of what the affected-rows value returned by this function means, See Section 27.7.6.1, “mysql_affected_rows()”.

Errors

None.

27.7.10.2 mysql_stmt_attr_get()

my_bool mysql_stmt_attr_get(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, void *arg)

Description

Can be used to get the current value for a statement attribute.

The option argument is the option that you want to get; the arg should point to a variable that should contain the option value. If the option is an integer, arg should point to the value of the integer.

See Section 27.7.10.3, “mysql_stmt_attr_set()”, for a list of options and option types.

Return Values

Zero for success. Nonzero if option is unknown.

Errors

None.

27.7.10.3 mysql_stmt_attr_set()

my_bool mysql_stmt_attr_set(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, const void *arg)

Description

Can be used to affect behavior for a prepared statement. This function may be called multiple times to set several options.

The option argument is the option that you want to set. The arg argument is the value for the option. arg should point to a variable that is set to the desired attribute value. The variable type is as indicated in the following table.

The following table shows the possible option values.

Option Argument Type Function
STMT_ATTR_UPDATE_MAX_LENGTH my_bool * If set to 1, causes mysql_stmt_store_result() to update the metadata MYSQL_FIELD->max_length value.
STMT_ATTR_CURSOR_TYPE unsigned long * Type of cursor to open for statement when mysql_stmt_execute() is invoked. *arg can be CURSOR_TYPE_NO_CURSOR (the default) or CURSOR_TYPE_READ_ONLY.
STMT_ATTR_PREFETCH_ROWS unsigned long * Number of rows to fetch from server at a time when using a cursor. *arg can be in the range from 1 to the maximum value of unsigned long. The default is 1.

If you use the STMT_ATTR_CURSOR_TYPE option with CURSOR_TYPE_READ_ONLY, a cursor is opened for the statement when you invoke mysql_stmt_execute(). If there is already an open cursor from a previous mysql_stmt_execute() call, it closes the cursor before opening a new one. mysql_stmt_reset() also closes any open cursor before preparing the statement for re-execution. mysql_stmt_free_result() closes any open cursor.

If you open a cursor for a prepared statement, mysql_stmt_store_result() is unnecessary, because that function causes the result set to be buffered on the client side.

Return Values

Zero for success. Nonzero if option is unknown.

Errors

None.

Example

The following example opens a cursor for a prepared statement and sets the number of rows to fetch at a time to 5:

MYSQL_STMT *stmt;
int rc;
unsigned long type;
unsigned long prefetch_rows = 5;

stmt = mysql_stmt_init(mysql);
type = (unsigned long) CURSOR_TYPE_READ_ONLY;
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, (void*) &type);
/* ... check return value ... */
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_PREFETCH_ROWS,
                         (void*) &prefetch_rows);
/* ... check return value ... */

27.7.10.4 mysql_stmt_bind_param()

my_bool mysql_stmt_bind_param(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_param() is used to bind input data for the parameter markers in the SQL statement that was passed to mysql_stmt_prepare(). It uses MYSQL_BIND structures to supply the data. bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each ? parameter marker that is present in the query.

Suppose that you prepare the following statement:

INSERT INTO mytbl VALUES(?,?,?)

When you bind the parameters, the array of MYSQL_BIND structures must contain three elements, and can be declared like this:

MYSQL_BIND bind[3];

Section 27.7.8, “C API Prepared Statement Data Structures”, describes the members of each MYSQL_BIND element and how they should be set to provide input values.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.10.5 mysql_stmt_bind_result()

my_bool mysql_stmt_bind_result(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_result() is used to associate (that is, bind) output columns in the result set to data buffers and length buffers. When mysql_stmt_fetch() is called to fetch data, the MySQL client/server protocol places the data for the bound columns into the specified buffers.

All columns must be bound to buffers prior to calling mysql_stmt_fetch(). bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each column of the result set. If you do not bind columns to MYSQL_BIND structures, mysql_stmt_fetch() simply ignores the data fetch. The buffers should be large enough to hold the data values, because the protocol does not return data values in chunks.

A column can be bound or rebound at any time, even after a result set has been partially retrieved. The new binding takes effect the next time mysql_stmt_fetch() is called. Suppose that an application binds the columns in a result set and calls mysql_stmt_fetch(). The client/server protocol returns data in the bound buffers. Then suppose that the application binds the columns to a different set of buffers. The protocol places data into the newly bound buffers when the next call to mysql_stmt_fetch() occurs.

To bind a column, an application calls mysql_stmt_bind_result() and passes the type, address, and length of the output buffer into which the value should be stored. Section 27.7.8, “C API Prepared Statement Data Structures”, describes the members of each MYSQL_BIND element and how they should be set to receive output values.

Return Values

Zero for success. Nonzero if an error occurred.

Errors
Example

See the Example in Section 27.7.10.11, “mysql_stmt_fetch()”.

27.7.10.6 mysql_stmt_close()

my_bool mysql_stmt_close(MYSQL_STMT *stmt)

Description

Closes the prepared statement. mysql_stmt_close() also deallocates the statement handler pointed to by stmt, which at that point becomes invalid and should no longer be used. For a failed mysql_stmt_close() call, do not call mysql_stmt_error(), or mysql_stmt_errno(), or mysql_stmt_sqlstate() to obtain error information because mysql_stmt_close() makes the statement handler invalid. Call mysql_error(), mysql_errno(), or mysql_sqlstate() instead.

If the current statement has pending or unread results, this function cancels them so that the next query can be executed.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.10.7 mysql_stmt_data_seek()

void mysql_stmt_data_seek(MYSQL_STMT *stmt, my_ulonglong offset)

Description

Seeks to an arbitrary row in a statement result set. The offset value is a row number and should be in the range from 0 to mysql_stmt_num_rows(stmt)-1.

This function requires that the statement result set structure contains the entire result of the last executed query, so mysql_stmt_data_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

None.

Errors

None.

27.7.10.8 mysql_stmt_errno()

unsigned int mysql_stmt_errno(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_errno() returns the error code for the most recently invoked statement API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix B, Errors, Error Codes, and Common Problems.

If the failed statement API function was mysql_stmt_close(), do not call or mysql_stmt_errno() to obtain error information because mysql_stmt_close() makes the statement handler invalid. Call mysql_errno() instead.

Return Values

An error code value. Zero if no error occurred.

Errors

None.

27.7.10.9 mysql_stmt_error()

const char *mysql_stmt_error(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_error() returns a null-terminated string containing the error message for the most recently invoked statement API function that can succeed or fail. An empty string ("") is returned if no error occurred. Either of these two tests can be used to check for an error:

if(*mysql_stmt_errno(stmt))
{
  // an error occurred
}

if (mysql_stmt_error(stmt)[0])
{
  // an error occurred
}

If the failed statement API function was mysql_stmt_close(), do not call mysql_stmt_error() to obtain error information because mysql_stmt_close() makes the statement handler invalid. Call mysql_error() instead.

The language of the client error messages may be changed by recompiling the MySQL client library. You can choose error messages in several different languages.

Return Values

A character string that describes the error. An empty string if no error occurred.

Errors

None.

27.7.10.10 mysql_stmt_execute()

int mysql_stmt_execute(MYSQL_STMT *stmt)

Description

mysql_stmt_execute() executes the prepared query associated with the statement handler. The currently bound parameter marker values are sent to server during this call, and the server replaces the markers with this newly supplied data.

Statement processing following mysql_stmt_execute() depends on the type of statement:

For statements that generate a result set, you can request that mysql_stmt_execute() open a cursor for the statement by calling mysql_stmt_attr_set() before executing the statement. If you execute a statement multiple times, mysql_stmt_execute() closes any open cursor before opening a new one.

Metadata changes to tables or views referred to by prepared statements are detected and cause automatic repreparation of the statement when it is next executed. For more information, see Section 8.10.4, “Caching of Prepared Statements and Stored Programs”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors
Example

The following example demonstrates how to create and populate a table using mysql_stmt_init(), mysql_stmt_prepare(), mysql_stmt_param_count(), mysql_stmt_bind_param(), mysql_stmt_execute(), and mysql_stmt_affected_rows(). The mysql variable is assumed to be a valid connection handler. For an example that shows how to retrieve data, see Section 27.7.10.11, “mysql_stmt_fetch()”.

#define STRING_SIZE 50

#define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table"
#define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(col1 INT,\
                                                 col2 VARCHAR(40),\
                                                 col3 SMALLINT,\
                                                 col4 TIMESTAMP)"
#define INSERT_SAMPLE "INSERT INTO \
                       test_table(col1,col2,col3) \
                       VALUES(?,?,?)"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[3];
my_ulonglong  affected_rows;
int           param_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
unsigned long str_length;
my_bool       is_null;

if (mysql_query(mysql, DROP_SAMPLE_TABLE))
{
  fprintf(stderr, " DROP TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

if (mysql_query(mysql, CREATE_SAMPLE_TABLE))
{
  fprintf(stderr, " CREATE TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

/* Prepare an INSERT query with 3 parameters */
/* (the TIMESTAMP column is not named; the server */
/*  sets it to the current date and time) */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_SAMPLE, strlen(INSERT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, INSERT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in INSERT: %d\n", param_count);

if (param_count != 3) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Bind the data for all 3 parameters */

memset(bind, 0, sizeof(bind));

/* INTEGER PARAM */
/* This is a number type, so there is no need
   to specify buffer_length */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= 0;
bind[0].length= 0;

/* STRING PARAM */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= 0;
bind[1].length= &str_length;

/* SMALLINT PARAM */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null;
bind[2].length= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_param() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Specify the data values for the first row */
int_data= 10;             /* integer */
strncpy(str_data, "MySQL", STRING_SIZE); /* string  */
str_length= strlen(str_data);

/* INSERT SMALLINT data as NULL */
is_null= 1;

/* Execute the INSERT statement - 1*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the number of affected rows */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 1): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Specify data values for second row,
   then re-execute the statement */
int_data= 1000;
strncpy(str_data, "
        The most popular Open Source database",
        STRING_SIZE);
str_length= strlen(str_data);
small_data= 1000;         /* smallint */
is_null= 0;               /* reset */

/* Execute the INSERT statement - 2*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute, 2 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the total rows affected */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 2): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Close the statement */
if (mysql_stmt_close(stmt))
{
  /* mysql_stmt_close() invalidates stmt, so call          */
  /* mysql_error(mysql) rather than mysql_stmt_error(stmt) */
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}
Note

For complete examples on the use of prepared statement functions, refer to the file tests/mysql_client_test.c. This file can be obtained from a MySQL source distribution or from the source repository (see Section 2.9, “Installing MySQL from Source”).

27.7.10.11 mysql_stmt_fetch()

int mysql_stmt_fetch(MYSQL_STMT *stmt)

Description

mysql_stmt_fetch() returns the next row in the result set. It can be called only while the result set exists; that is, after a call to mysql_stmt_execute() for a statement such as SELECT that produces a result set.

mysql_stmt_fetch() returns row data using the buffers bound by mysql_stmt_bind_result(). It returns the data in those buffers for all the columns in the current row set and the lengths are returned to the length pointer. All columns must be bound by the application before it calls mysql_stmt_fetch().

mysql_stmt_fetch() typically occurs within a loop, to ensure that all result set rows are fetched. For example:

int status;

while (1)
{
  status = mysql_stmt_fetch(stmt);

  if (status == 1 || status == MYSQL_NO_DATA)
    break;

  /* handle current row here */
}

/* if desired, handle status == 1 case and display error here */

By default, result sets are fetched unbuffered a row at a time from the server. To buffer the entire result set on the client, call mysql_stmt_store_result() after binding the data buffers and before calling mysql_stmt_fetch().

If a fetched data value is a NULL value, the *is_null value of the corresponding MYSQL_BIND structure contains TRUE (1). Otherwise, the data and its length are returned in the *buffer and *length elements based on the buffer type specified by the application. Each numeric and temporal type has a fixed length, as listed in the following table. The length of the string types depends on the length of the actual data value, as indicated by data_length.

Type Length
MYSQL_TYPE_TINY 1
MYSQL_TYPE_SHORT 2
MYSQL_TYPE_LONG 4
MYSQL_TYPE_LONGLONG 8
MYSQL_TYPE_FLOAT 4
MYSQL_TYPE_DOUBLE 8
MYSQL_TYPE_TIME sizeof(MYSQL_TIME)
MYSQL_TYPE_DATE sizeof(MYSQL_TIME)
MYSQL_TYPE_DATETIME sizeof(MYSQL_TIME)
MYSQL_TYPE_STRING data length
MYSQL_TYPE_BLOB data_length

In some cases, you might want to determine the length of a column value before fetching it with mysql_stmt_fetch(). For example, the value might be a long string or BLOB value for which you want to know how much space must be allocated. To accomplish this, use one of these strategies:

  • Before invoking mysql_stmt_fetch() to retrieve individual rows, pass STMT_ATTR_UPDATE_MAX_LENGTH to mysql_stmt_attr_set(), then invoke mysql_stmt_store_result() to buffer the entire result on the client side. Setting the STMT_ATTR_UPDATE_MAX_LENGTH attribute causes the maximal length of column values to be indicated by the max_length member of the result set metadata returned by mysql_stmt_result_metadata().

  • Invoke mysql_stmt_fetch() with a zero-length buffer for the column in question and a pointer in which the real length can be stored. Then use the real length with mysql_stmt_fetch_column().

    real_length= 0;
    
    bind[0].buffer= 0;
    bind[0].buffer_length= 0;
    bind[0].length= &real_length
    mysql_stmt_bind_result(stmt, bind);
    
    mysql_stmt_fetch(stmt);
    if (real_length > 0)
    {
      data= malloc(real_length);
      bind[0].buffer= data;
      bind[0].buffer_length= real_length;
      mysql_stmt_fetch_column(stmt, bind, 0, 0);
    }
Return Values
Return Value Description
0 Success, the data has been fetched to application data buffers.
1 Error occurred. Error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().
MYSQL_NO_DATA Success, no more data exists
MYSQL_DATA_TRUNCATED Data truncation occurred

MYSQL_DATA_TRUNCATED is returned when truncation reporting is enabled. To determine which column values were truncated when this value is returned, check the error members of the MYSQL_BIND structures used for fetching values. Truncation reporting is enabled by default, but can be controlled by calling mysql_options() with the MYSQL_REPORT_DATA_TRUNCATION option.

Errors
Example

The following example demonstrates how to fetch data from a table using mysql_stmt_result_metadata(), mysql_stmt_bind_result(), and mysql_stmt_fetch(). (This example expects to retrieve the two rows inserted by the example shown in Section 27.7.10.10, “mysql_stmt_execute()”.) The mysql variable is assumed to be a valid connection handler.

#define STRING_SIZE 50

#define SELECT_SAMPLE "SELECT col1, col2, col3, col4 \
                       FROM test_table"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[4];
MYSQL_RES     *prepare_meta_result;
MYSQL_TIME    ts;
unsigned long length[4];
int           param_count, column_count, row_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
my_bool       is_null[4];
my_bool       error[4];

/* Prepare a SELECT query to fetch data from test_table */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, SELECT_SAMPLE, strlen(SELECT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), SELECT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, SELECT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in SELECT: %d\n", param_count);

if (param_count != 0) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Fetch result set meta information */
prepare_meta_result = mysql_stmt_result_metadata(stmt);
if (!prepare_meta_result)
{
  fprintf(stderr,
         " mysql_stmt_result_metadata(), \
           returned no meta information\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get total columns in the query */
column_count= mysql_num_fields(prepare_meta_result);
fprintf(stdout,
        " total columns in SELECT statement: %d\n",
        column_count);

if (column_count != 4) /* validate column count */
{
  fprintf(stderr, " invalid column count returned by MySQL\n");
  exit(0);
}

/* Execute the SELECT query */
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Bind the result buffers for all 4 columns before fetching them */

memset(bind, 0, sizeof(bind));

/* INTEGER COLUMN */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= &is_null[0];
bind[0].length= &length[0];
bind[0].error= &error[0];

/* STRING COLUMN */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= &is_null[1];
bind[1].length= &length[1];
bind[1].error= &error[1];

/* SMALLINT COLUMN */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null[2];
bind[2].length= &length[2];
bind[2].error= &error[2];

/* TIMESTAMP COLUMN */
bind[3].buffer_type= MYSQL_TYPE_TIMESTAMP;
bind[3].buffer= (char *)&ts;
bind[3].is_null= &is_null[3];
bind[3].length= &length[3];
bind[3].error= &error[3];

/* Bind the result buffers */
if (mysql_stmt_bind_result(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Now buffer all results to client (optional step) */
if (mysql_stmt_store_result(stmt))
{
  fprintf(stderr, " mysql_stmt_store_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Fetch all rows */
row_count= 0;
fprintf(stdout, "Fetching results ...\n");
while (!mysql_stmt_fetch(stmt))
{
  row_count++;
  fprintf(stdout, "  row %d\n", row_count);

  /* column 1 */
  fprintf(stdout, "   column1 (integer)  : ");
  if (is_null[0])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", int_data, length[0]);

  /* column 2 */
  fprintf(stdout, "   column2 (string)   : ");
  if (is_null[1])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %s(%ld)\n", str_data, length[1]);

  /* column 3 */
  fprintf(stdout, "   column3 (smallint) : ");
  if (is_null[2])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", small_data, length[2]);

  /* column 4 */
  fprintf(stdout, "   column4 (timestamp): ");
  if (is_null[3])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %04d-%02d-%02d %02d:%02d:%02d (%ld)\n",
                     ts.year, ts.month, ts.day,
                     ts.hour, ts.minute, ts.second,
                     length[3]);
  fprintf(stdout, "\n");
}

/* Validate rows fetched */
fprintf(stdout, " total rows fetched: %d\n", row_count);
if (row_count != 2)
{
  fprintf(stderr, " MySQL failed to return all rows\n");
  exit(0);
}

/* Free the prepared result metadata */
mysql_free_result(prepare_meta_result);


/* Close the statement */
if (mysql_stmt_close(stmt))
{
  /* mysql_stmt_close() invalidates stmt, so call          */
  /* mysql_error(mysql) rather than mysql_stmt_error(stmt) */
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

27.7.10.12 mysql_stmt_fetch_column()

int mysql_stmt_fetch_column(MYSQL_STMT *stmt, MYSQL_BIND *bind, unsigned int column, unsigned long offset)

Description

Fetches one column from the current result set row. bind provides the buffer where data should be placed. It should be set up the same way as for mysql_stmt_bind_result(). column indicates which column to fetch. The first column is numbered 0. offset is the offset within the data value at which to begin retrieving data. This can be used for fetching the data value in pieces. The beginning of the value is offset 0.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.10.13 mysql_stmt_field_count()

unsigned int mysql_stmt_field_count(MYSQL_STMT *stmt)

Description

Returns the number of columns for the most recent statement for the statement handler. This value is zero for statements such as INSERT or DELETE that do not produce result sets.

mysql_stmt_field_count() can be called after you have prepared a statement by invoking mysql_stmt_prepare().

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

27.7.10.14 mysql_stmt_free_result()

my_bool mysql_stmt_free_result(MYSQL_STMT *stmt)

Description

Releases memory associated with the result set produced by execution of the prepared statement. If there is a cursor open for the statement, mysql_stmt_free_result() closes it.

Return Values

Zero for success. Nonzero if an error occurred.

27.7.10.15 mysql_stmt_init()

MYSQL_STMT *mysql_stmt_init(MYSQL *mysql)

Description

Creates and returns a MYSQL_STMT handler. The handler should be freed with mysql_stmt_close(), at which point the handler becomes invalid and should no longer be used.

See also Section 27.7.8, “C API Prepared Statement Data Structures”, for more information.

Return Values

A pointer to a MYSQL_STMT structure in case of success. NULL if out of memory.

Errors

27.7.10.16 mysql_stmt_insert_id()

my_ulonglong mysql_stmt_insert_id(MYSQL_STMT *stmt)

Description

Returns the value generated for an AUTO_INCREMENT column by the prepared INSERT or UPDATE statement. Use this function after you have executed a prepared INSERT statement on a table which contains an AUTO_INCREMENT field.

See Section 27.7.6.38, “mysql_insert_id()”, for more information.

Return Values

Value for AUTO_INCREMENT column which was automatically generated or explicitly set during execution of prepared statement, or value generated by LAST_INSERT_ID(expr) function. Return value is undefined if statement does not set AUTO_INCREMENT value.

Errors

None.

27.7.10.17 mysql_stmt_next_result()

int mysql_stmt_next_result(MYSQL_STMT *mysql)

Description

This function is used when you use prepared CALL statements to execute stored procedures, which can return multiple result sets. Use a loop that calls mysql_stmt_next_result() to determine whether there are more results. If a procedure has OUT or INOUT parameters, their values will be returned as a single-row result set following any other result sets. The values will appear in the order in which they are declared in the procedure parameter list.

For information about the effect of unhandled conditions on procedure parameters, see Section 13.6.7.8, “Condition Handling and OUT or INOUT Parameters”.

mysql_stmt_next_result() returns a status to indicate whether more results exist. If mysql_stmt_next_result() returns an error, there are no more results.

Before each call to mysql_stmt_next_result(), you must call mysql_stmt_free_result() for the current result if it produced a result set (rather than just a result status).

After calling mysql_stmt_next_result() the state of the connection is as if you had called mysql_stmt_execute(). This means that you can call mysql_stmt_bind_result(), mysql_stmt_affected_rows(), and so forth.

It is also possible to test whether there are more results by calling mysql_more_results(). However, this function does not change the connection state, so if it returns true, you must still call mysql_stmt_next_result() to advance to the next result.

For an example that shows how to use mysql_stmt_next_result(), see Section 27.7.17, “C API Prepared CALL Statement Support”.

Return Values
Return Value Description
0 Successful and there are more results
-1 Successful and there are no more results
>0 An error occurred
Errors

27.7.10.18 mysql_stmt_num_rows()

my_ulonglong mysql_stmt_num_rows(MYSQL_STMT *stmt)

Description

Returns the number of rows in the result set.

The use of mysql_stmt_num_rows() depends on whether you used mysql_stmt_store_result() to buffer the entire result set in the statement handler. If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately. Otherwise, the row count is unavailable unless you count the rows as you fetch them.

mysql_stmt_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_stmt_affected_rows().

Return Values

The number of rows in the result set.

Errors

None.

27.7.10.19 mysql_stmt_param_count()

unsigned long mysql_stmt_param_count(MYSQL_STMT *stmt)

Description

Returns the number of parameter markers present in the prepared statement.

Return Values

An unsigned long integer representing the number of parameters in a statement.

Errors

None.

27.7.10.20 mysql_stmt_param_metadata()

MYSQL_RES *mysql_stmt_param_metadata(MYSQL_STMT *stmt)

This function currently does nothing.

27.7.10.21 mysql_stmt_prepare()

int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *stmt_str, unsigned long length)

Description

Given the statement handler returned by mysql_stmt_init(), prepares the SQL statement pointed to by the string stmt_str and returns a status value. The string length should be given by the length argument. The string must consist of a single SQL statement. You should not add a terminating semicolon (;) or \g to the statement.

The application can include one or more parameter markers in the SQL statement by embedding question mark (?) characters into the SQL string at the appropriate positions.

The markers are legal only in certain places in SQL statements. For example, they are permitted in the VALUES() list of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value. However, they are not permitted for identifiers (such as table or column names), or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. In general, parameters are legal only in Data Manipulation Language (DML) statements, and not in Data Definition Language (DDL) statements.

The parameter markers must be bound to application variables using mysql_stmt_bind_param() before executing the statement.

Metadata changes to tables or views referred to by prepared statements are detected and cause automatic repreparation of the statement when it is next executed. For more information, see Section 8.10.4, “Caching of Prepared Statements and Stored Programs”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

If the prepare operation was unsuccessful (that is, mysql_stmt_prepare() returns nonzero), the error message can be obtained by calling mysql_stmt_error().

27.7.10.22 mysql_stmt_reset()

my_bool mysql_stmt_reset(MYSQL_STMT *stmt)

Description

Resets a prepared statement on client and server to state after prepare. It resets the statement on the server, data sent using mysql_stmt_send_long_data(), unbuffered result sets and current errors. It does not clear bindings or stored result sets. Stored result sets will be cleared when executing the prepared statement (or closing it).

To re-prepare the statement with another query, use mysql_stmt_prepare().

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.10.23 mysql_stmt_result_metadata()

MYSQL_RES *mysql_stmt_result_metadata(MYSQL_STMT *stmt)

Description

If a statement passed to mysql_stmt_prepare() is one that produces a result set, mysql_stmt_result_metadata() returns the result set metadata in the form of a pointer to a MYSQL_RES structure that can be used to process the meta information such as number of fields and individual field information. This result set pointer can be passed as an argument to any of the field-based API functions that process result set metadata, such as:

The result set structure should be freed when you are done with it, which you can do by passing it to mysql_free_result(). This is similar to the way you free a result set obtained from a call to mysql_store_result().

The result set returned by mysql_stmt_result_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handler with mysql_stmt_fetch().

Return Values

A MYSQL_RES result structure. NULL if no meta information exists for the prepared query.

Errors
Example

See the Example in Section 27.7.10.11, “mysql_stmt_fetch()”.

27.7.10.24 mysql_stmt_row_seek()

MYSQL_ROW_OFFSET mysql_stmt_row_seek(MYSQL_STMT *stmt, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a statement result set. The offset value is a row offset that should be a value returned from mysql_stmt_row_tell() or from mysql_stmt_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_stmt_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_stmt_row_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_stmt_row_seek().

Errors

None.

27.7.10.25 mysql_stmt_row_tell()

MYSQL_ROW_OFFSET mysql_stmt_row_tell(MYSQL_STMT *stmt)

Description

Returns the current position of the row cursor for the last mysql_stmt_fetch(). This value can be used as an argument to mysql_stmt_row_seek().

You should use mysql_stmt_row_tell() only after mysql_stmt_store_result().

Return Values

The current offset of the row cursor.

Errors

None.

27.7.10.26 mysql_stmt_send_long_data()

my_bool mysql_stmt_send_long_data(MYSQL_STMT *stmt, unsigned int parameter_number, const char *data, unsigned long length)

Description

Enables an application to send parameter data to the server in pieces (or chunks). Call this function after mysql_stmt_bind_param() and before mysql_stmt_execute(). It can be called multiple times to send the parts of a character or binary data value for a column, which must be one of the TEXT or BLOB data types.

parameter_number indicates which parameter to associate the data with. Parameters are numbered beginning with 0. data is a pointer to a buffer containing data to be sent, and length indicates the number of bytes in the buffer.

Note

The next mysql_stmt_execute() call ignores the bind buffer for all parameters that have been used with mysql_stmt_send_long_data() since last mysql_stmt_execute() or mysql_stmt_reset().

If you want to reset/forget the sent data, you can do it with mysql_stmt_reset(). See Section 27.7.10.22, “mysql_stmt_reset()”.

The max_allowed_packet system variable controls the maximum size of parameter values that can be sent with mysql_stmt_send_long_data().

Return Values

Zero for success. Nonzero if an error occurred.

Errors
Example

The following example demonstrates how to send the data for a TEXT column in chunks. It inserts the data value 'MySQL - The most popular Open Source database' into the text_column column. The mysql variable is assumed to be a valid connection handler.

#define INSERT_QUERY "INSERT INTO \
                      test_long_data(text_column) VALUES(?)"

MYSQL_BIND bind[1];
long       length;

stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_QUERY, strlen(INSERT_QUERY)))
{
  fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}
 memset(bind, 0, sizeof(bind));
 bind[0].buffer_type= MYSQL_TYPE_STRING;
 bind[0].length= &length;
 bind[0].is_null= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, "\n param bind failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply data in chunks to server */
 if (mysql_stmt_send_long_data(stmt,0,"MySQL",5))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply the next piece of data */
 if (mysql_stmt_send_long_data(stmt,0,
           " - The most popular Open Source database",40))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Now, execute the query */
 if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, "\n mysql_stmt_execute failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

27.7.10.27 mysql_stmt_sqlstate()

const char *mysql_stmt_sqlstate(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_sqlstate() returns a null-terminated string containing the SQLSTATE error code for the most recently invoked prepared statement API function that can succeed or fail. The error code consists of five characters. "00000" means no error. The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix B, Errors, Error Codes, and Common Problems.

Not all MySQL errors are mapped to SQLSTATE codes. The value "HY000" (general error) is used for unmapped errors.

If the failed statement API function was mysql_stmt_close(), do not call mysql_stmt_sqlstate() to obtain error information because mysql_stmt_close() makes the statement handler invalid. Call mysql_sqlstate() instead.

Return Values

A null-terminated character string containing the SQLSTATE error code.

27.7.10.28 mysql_stmt_store_result()

int mysql_stmt_store_result(MYSQL_STMT *stmt)

Description

Result sets are produced by calling mysql_stmt_execute() to executed prepared statements for SQL statements such as SELECT, SHOW, DESCRIBE, and EXPLAIN. By default, result sets for successfully executed prepared statements are not buffered on the client and mysql_stmt_fetch() fetches them one at a time from the server. To cause the complete result set to be buffered on the client, call mysql_stmt_store_result() after binding data buffers with mysql_stmt_bind_result() and before calling mysql_stmt_fetch() to fetch rows. (For an example, see Section 27.7.10.11, “mysql_stmt_fetch()”.)

mysql_stmt_store_result() is optional for result set processing, unless you will call mysql_stmt_data_seek(), mysql_stmt_row_seek(), or mysql_stmt_row_tell(). Those functions require a seekable result set.

It is unnecessary to call mysql_stmt_store_result() after executing an SQL statement that does not produce a result set, but if you do, it does not harm or cause any notable performance problem. You can detect whether the statement produced a result set by checking if mysql_stmt_result_metadata() returns NULL. For more information, refer to Section 27.7.10.23, “mysql_stmt_result_metadata()”.

Note

MySQL does not by default calculate MYSQL_FIELD->max_length for all columns in mysql_stmt_store_result() because calculating this would slow down mysql_stmt_store_result() considerably and most applications do not need max_length. If you want max_length to be updated, you can call mysql_stmt_attr_set(MYSQL_STMT, STMT_ATTR_UPDATE_MAX_LENGTH, &flag) to enable this. See Section 27.7.10.3, “mysql_stmt_attr_set()”.

Return Values

Zero for success. Nonzero if an error occurred.

Errors

27.7.11 C API Threaded Function Descriptions

To create a threaded client, use the functions described in the following sections. See also Section 27.7.3.3, “Writing C API Threaded Client Programs”.

27.7.11.1 my_init()

void my_init(void)

Description

my_init() initializes some global variables that MySQL needs. It also calls mysql_thread_init() for this thread.

It is necessary for my_init() to be called early in the initialization phase of a program's use of the MySQL client library. However, my_init() is automatically called by mysql_init(), mysql_library_init(), mysql_server_init(), and mysql_connect(). If you ensure that your program invokes one of those functions before any other MySQL calls, there is no need to invoke my_init() explicitly.

To access the prototype for my_init(), your program should include these header files:

#include <my_global.h>
#include <my_sys.h>
Return Values

None.

27.7.11.2 mysql_thread_end()

void mysql_thread_end(void)

Description

Call this function as necessary before calling pthread_exit() to free memory allocated by mysql_thread_init():

mysql_thread_end() is not invoked automatically by the client library.

Return Values

None.

27.7.11.3 mysql_thread_init()

my_bool mysql_thread_init(void)

Description

This function must be called early within each created thread to initialize thread-specific variables. However, it may be unnecessarily to invoke it explicitly. Calling mysql_thread_init() is automatically handled my_init(), which itself is called by mysql_init(), mysql_library_init(), mysql_server_init(), and mysql_connect(). If you invoke any of those functions, mysql_thread_init() is called for you.

Return Values

Zero for success. Nonzero if an error occurred.

27.7.11.4 mysql_thread_safe()

unsigned int mysql_thread_safe(void)

Description

This function indicates whether the client library is compiled as thread-safe.

Return Values

1 if the client library is thread-safe, 0 otherwise.

27.7.12 C API Embedded Server Function Descriptions

MySQL applications can be written to use an embedded server. See Section 27.6, “libmysqld, the Embedded MySQL Server Library”. To write such an application, you must link it against the libmysqld library by using the -lmysqld flag rather than linking it against the libmysqlclient client library by using the -lmysqlclient flag. However, the calls to initialize and finalize the library are the same whether you write a client application or one that uses the embedded server: Call mysql_library_init() to initialize the library and mysql_library_end() when you are done with it. See Section 27.7.5, “C API Function Overview”.

27.7.12.1 mysql_server_end()

void mysql_server_end(void)

Description

This function finalizes the MySQL library, which should be done when you are done using the library. However, mysql_server_end() is deprecated and mysql_library_end() should be used instead. See Section 27.7.6.40, “mysql_library_end()”.

Note

To avoid memory leaks after the application is done using the library (for example, after closing the connection to the server), be sure to call mysql_server_end() (or mysql_library_end()) explicitly. This enables memory managment to be performed to clean up and free resources used by the library.

Return Values

None.

27.7.12.2 mysql_server_init()

int mysql_server_init(int argc, char **argv, char **groups)

Description

This function initializes the MySQL client library, which must be done before you call any other MySQL function. However, mysql_server_init() is deprecated and you should call mysql_library_init() instead. See Section 27.7.6.41, “mysql_library_init()”.

Note

To avoid memory leaks after the application is done using the library (for example, after closing the connection to the server), be sure to call mysql_server_end() (or mysql_library_end()) explicitly. This enables memory managment to be performed to clean up and free resources used by the library. See Section 27.7.6.40, “mysql_library_end()”.

Return Values

Zero for success. Nonzero if an error occurred.

27.7.13 C API Client Plugin Functions

This section describes functions used for the client-side plugin API. They enable management of client plugins. For a description of the st_mysql_client_plugin structure used by these functions, see Section 28.2.4.2.3, “Client Plugin Descriptors”.

It is unlikely that a client program needs to call the functions in this section. For example, a client that supports the use of authentication plugins normally causes a plugin to be loaded by calling mysql_options() to set the MYSQL_DEFAULT_AUTH and MYSQL_PLUGIN_DIR options:

char *plugin_dir = "path_to_plugin_dir";
char *default_auth = "plugin_name";

/* ... process command-line options ... */

mysql_options(&mysql, MYSQL_PLUGIN_DIR, plugin_dir);
mysql_options(&mysql, MYSQL_DEFAULT_AUTH, default_auth);

Typically, the program will also accept --plugin-dir and --default-auth options that enable users to override the default values.

27.7.13.1 mysql_client_find_plugin()

struct st_mysql_client_plugin *mysql_client_find_plugin(MYSQL *mysql, const char *name, int type)

Description

Returns a pointer to a loaded plugin, loading the plugin first if necessary. An error occurs if the type is invalid or the plugin cannot be found or loaded.

Specify the parameters as follows:

  • mysql: A pointer to a MYSQL structure. The plugin API does not require a connection to a MySQL server, but this structure must be properly initialized. The structure is used to obtain connection-related information.

  • name: The plugin name.

  • type: The plugin type.

Return Values

A pointer to the plugin for success. NULL if an error occurred.

Example
MYSQL mysql;
struct st_mysql_client_plugin *p;

if ((p = mysql_client_find_plugin(&mysql, "myplugin",
                                  MYSQL_CLIENT_AUTHENTICATION_PLUGIN, 0)))
{
  printf("Plugin version: %d.%d.%d\n", p->version[0], p->version[1], p->version[2]);
}

27.7.13.2 mysql_client_register_plugin()

struct st_mysql_client_plugin *mysql_client_register_plugin(MYSQL *mysql, struct st_mysql_client_plugin *plugin)

Description

Adds a plugin structure to the list of loaded plugins. An error occurs if the plugin is already loaded.

Specify the parameters as follows:

  • mysql: A pointer to a MYSQL structure. The plugin API does not require a connection to a MySQL server, but this structure must be properly initialized. The structure is used to obtain connection-related information.

  • plugin: A pointer to the plugin structure.

Return Values

A pointer to the plugin for success. NULL if an error occurred.

27.7.13.3 mysql_load_plugin()

struct st_mysql_client_plugin *mysql_load_plugin(MYSQL *mysql, const char *name, int type, int argc, ...)

Description

Loads a MySQL client plugin, specified by name and type. An error occurs if the type is invalid or the plugin cannot be loaded.

It is not possible to load multiple plugins of the same type. An error occurs if you try to load a plugin of a type already loaded.

Specify the parameters as follows:

  • mysql: A pointer to a MYSQL structure. The plugin API does not require a connection to a MySQL server, but this structure must be properly initialized. The structure is used to obtain connection-related information.

  • name: The name of the plugin to load.

  • type: The type of plugin to load, or −1 to disable type checking. If type is not −1, only plugins matching the type are considered for loading.

  • argc: The number of following arguments (0 if there are none). Interpretation of any following arguments depends on the plugin type.

Another way to cause plugins to be loaded is to set the LIBMYSQL_PLUGINS environment variable to a list of semicolon-separated plugin names. For example:

export LIBMYSQL_PLUGINS="myplugin1;myplugin2"

Plugins named by LIBMYSQL_PLUGINS are loaded when the client program calls mysql_library_init(). No error is reported if problems occur loading these plugins.

The LIBMYSQL_PLUGIN_DIR environment variable can be set to the path name of the directory in which to look for client plugins. This variable is used in two ways:

  • During client plugin preloading, the value of the --plugin-dir option is not available, so client plugin loading fails unless the plugins are located in the hardwired default directory. If the plugins are located elsewhere, LIBMYSQL_PLUGIN_DIR environment variable can be set to the proper directory to enable plugin preloading to succeed.

  • For explicit client plugin loading, the mysql_load_plugin() and mysql_load_plugin_v() C API functions use the LIBMYSQL_PLUGIN_DIR value if it exists and the --plugin-dir option was not given. If --plugin-dir is given, mysql_load_plugin() and mysql_load_plugin_v() ignore LIBMYSQL_PLUGIN_DIR.

Return Values

A pointer to the plugin if it was loaded successfully. NULL if an error occurred.

Example
MYSQL mysql;

if(!mysql_load_plugin(&mysql, "myplugin",
                      MYSQL_CLIENT_AUTHENTICATION_PLUGIN, 0))
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
    exit(-1);
}

27.7.13.4 mysql_load_plugin_v()

struct st_mysql_client_plugin *mysql_load_plugin_v(MYSQL *mysql, const char *name, int type, int argc, va_list args)

Description

This function is equivalent to mysql_load_plugin(), but it accepts a va_list instead of a variable list of parameters.

27.7.13.5 mysql_plugin_options()

int mysql_plugin_options(struct st_mysql_client_plugin *plugin, const char *option, const void *value)

Description

Passes an option type and value to a plugin. This function can be called multiple times to set several options. If the plugin does not have an option handler, an error occurs.

Specify the parameters as follows:

  • plugin: A pointer to the plugin structure.

  • option: The option to be set.

  • value: A pointer to the option value.

Return Values

Zero for success, 1 if an error occurred. If the plugin has an option handler, that handler should also return zero for success and 1 if an error occurred.

27.7.14 C API Encrypted Connection Support

This section describes how C applications use the C API capabilities for encrypted connections. By default, MySQL programs attempt to connect using encryption if the server supports encrypted connections, falling back to an unencrypted connection if an encrypted connection cannot be established (see Section 6.3.1, “Configuring MySQL to Use Encrypted Connections”). For applications that require control beyond the default behavior over how encrypted connections are established, the C API provides these capabilities:

C API Options for Encrypted Connections

mysql_options() provides the following options for control over use of encrypted connections. For option details, see Section 27.7.6.50, “mysql_options()”.

  • MYSQL_OPT_SSL_CA: The path name of the Certificate Authority (CA) certificate file. This option, if used, must specify the same certificate used by the server.

  • MYSQL_OPT_SSL_CAPATH: The path name of the directory that contains trusted SSL CA certificate files.

  • MYSQL_OPT_SSL_CERT: The path name of the client public key certificate file.

  • MYSQL_OPT_SSL_CIPHER: The list of permissible ciphers for SSL encryption.

  • MYSQL_OPT_SSL_CRL: The path name of the file containing certificate revocation lists.

  • MYSQL_OPT_SSL_CRLPATH: The path name of the directory that contains certificate revocation list files.

  • MYSQL_OPT_SSL_KEY: The path name of the client private key file.

  • MYSQL_OPT_SSL_MODE: The connection security state.

  • MYSQL_OPT_SSL_VERIFY_SERVER_CERT: Whether to perform host name identity verification of the server certificate Common Name value.

  • MYSQL_OPT_TLS_VERSION: The encryption protocols the client permits.

mysql_ssl_set() can be used as a convenience routine that is equivalent to a set of mysql_options() calls that specify certificate and key files, encryption ciphers, and so forth. See Section 27.7.6.73, “mysql_ssl_set()”.

Enforcing an Encrypted Connection

mysql_options() options for information such as SSL certificate and key files are used to establish an encrypted connection if such connections are available, but do not enforce any requirement that the connection obtained be encrypted. To require an encrypted connection, use the following technique:

  1. Call mysql_options() as necessary supply the appropriate SSL parameters (certificate and key files, encryption ciphers, and so forth).

  2. Call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_REQUIRED or one of the more-restrictive option values.

  3. Call mysql_real_connect() to connect to the server. The call fails if an encrypted connection cannot be obtained; exit with an error.

Improving Security of Encrypted Connections

For additional security relative to that provided by the default encryption, clients can supply a CA certificate matching the one used by the server and enable host name identity verification. In this way, the server and client place their trust in the same CA certificate and the client verifies that the host to which it connected is the one intended:

  • To specify the CA certificate, call mysql_options() to pass the MYSQL_OPT_SSL_CA (or MYSQL_OPT_SSL_CAPATH) option, and call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_VERIFY_CA.

  • To enable host name identity verification as well, call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_VERIFY_IDENTITY rather than SSL_MODE_VERIFY_CA.

Note

Host name identity verification with SSL_MODE_VERIFY_IDENTITY does not work with self-signed certificates created automatically by the server, or manually using mysql_ssl_rsa_setup (see Section 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”). Such self-signed certificates do not contain the server name as the Common Name value.

Host name identity verification also does not work with certificates that specify the Common Name using wildcards because that name is compared verbatim to the server name.

27.7.15 C API Multiple Statement Execution Support

By default, mysql_query() and mysql_real_query() interpret their statement string argument as a single statement to be executed, and you process the result according to whether the statement produces a result set (a set of rows, as for SELECT) or an affected-rows count (as for INSERT, UPDATE, and so forth).

MySQL also supports the execution of a string containing multiple statements separated by semicolon (;) characters. This capability is enabled by special options that are specified either when you connect to the server with mysql_real_connect() or after connecting by calling mysql_set_server_option().

Executing a multiple-statement string can produce multiple result sets or row-count indicators. Processing these results involves a different approach than for the single-statement case: After handling the result from the first statement, it is necessary to check whether more results exist and process them in turn if so. To support multiple-result processing, the C API includes the mysql_more_results() and mysql_next_result() functions. These functions are used at the end of a loop that iterates as long as more results are available. Failure to process the result this way may result in a dropped connection to the server.

Multiple-result processing also is required if you execute CALL statements for stored procedures. Results from a stored procedure have these characteristics:

  • Statements within the procedure may produce result sets (for example, if it executes SELECT statements). These result sets are returned in the order that they are produced as the procedure executes.

    In general, the caller cannot know how many result sets a procedure will return. Procedure execution may depend on loops or conditional statements that cause the execution path to differ from one call to the next. Therefore, you must be prepared to retrieve multiple results.

  • The final result from the procedure is a status result that includes no result set. The status indicates whether the procedure succeeded or an error occurred.

The multiple statement and result capabilities can be used only with mysql_query() or mysql_real_query(). They cannot be used with the prepared statement interface. Prepared statement handlers are defined to work only with strings that contain a single statement. See Section 27.7.7, “C API Prepared Statements”.

To enable multiple-statement execution and result processing, the following options may be used:

  • The mysql_real_connect() function has a flags argument for which two option values are relevant:

    • CLIENT_MULTI_RESULTS enables the client program to process multiple results. This option must be enabled if you execute CALL statements for stored procedures that produce result sets. Otherwise, such procedures result in an error Error 1312 (0A000): PROCEDURE proc_name can't return a result set in the given context. In MySQL 5.7, CLIENT_MULTI_RESULTS is enabled by default.

    • CLIENT_MULTI_STATEMENTS enables mysql_query() and mysql_real_query() to execute statement strings containing multiple statements separated by semicolons. This option also enables CLIENT_MULTI_RESULTS implicitly, so a flags argument of CLIENT_MULTI_STATEMENTS to mysql_real_connect() is equivalent to an argument of CLIENT_MULTI_STATEMENTS | CLIENT_MULTI_RESULTS. That is, CLIENT_MULTI_STATEMENTS is sufficient to enable multiple-statement execution and all multiple-result processing.

  • After the connection to the server has been established, you can use the mysql_set_server_option() function to enable or disable multiple-statement execution by passing it an argument of MYSQL_OPTION_MULTI_STATEMENTS_ON or MYSQL_OPTION_MULTI_STATEMENTS_OFF. Enabling multiple-statement execution with this function also enables processing of simple results for a multiple-statement string where each statement produces a single result, but is not sufficient to permit processing of stored procedures that produce result sets.

The following procedure outlines a suggested strategy for handling multiple statements:

  1. Pass CLIENT_MULTI_STATEMENTS to mysql_real_connect(), to fully enable multiple-statement execution and multiple-result processing.

  2. After calling mysql_query() or mysql_real_query() and verifying that it succeeds, enter a loop within which you process statement results.

  3. For each iteration of the loop, handle the current statement result, retrieving either a result set or an affected-rows count. If an error occurs, exit the loop.

  4. At the end of the loop, call mysql_next_result() to check whether another result exists and initiate retrieval for it if so. If no more results are available, exit the loop.

One possible implementation of the preceding strategy is shown following. The final part of the loop can be reduced to a simple test of whether mysql_next_result() returns nonzero. The code as written distinguishes between no more results and an error, which enables a message to be printed for the latter occurrence.

/* connect to server with the CLIENT_MULTI_STATEMENTS option */
if (mysql_real_connect (mysql, host_name, user_name, password,
    db_name, port_num, socket_name, CLIENT_MULTI_STATEMENTS) == NULL)
{
  printf("mysql_real_connect() failed\n");
  mysql_close(mysql);
  exit(1);
}

/* execute multiple statements */
status = mysql_query(mysql,
                     "DROP TABLE IF EXISTS test_table;\
                      CREATE TABLE test_table(id INT);\
                      INSERT INTO test_table VALUES(10);\
                      UPDATE test_table SET id=20 WHERE id=10;\
                      SELECT * FROM test_table;\
                      DROP TABLE test_table");
if (status)
{
  printf("Could not execute statement(s)");
  mysql_close(mysql);
  exit(0);
}

/* process each statement result */
do {
  /* did current statement return data? */
  result = mysql_store_result(mysql);
  if (result)
  {
    /* yes; process rows and free the result set */
    process_result_set(mysql, result);
    mysql_free_result(result);
  }
  else          /* no result set or error */
  {
    if (mysql_field_count(mysql) == 0)
    {
      printf("%lld rows affected\n",
            mysql_affected_rows(mysql));
    }
    else  /* some error occurred */
    {
      printf("Could not retrieve result set\n");
      break;
    }
  }
  /* more results? -1 = no, >0 = error, 0 = yes (keep looping) */
  if ((status = mysql_next_result(mysql)) > 0)
    printf("Could not execute statement\n");
} while (status == 0);

mysql_close(mysql);

27.7.16 C API Prepared Statement Handling of Date and Time Values

The binary (prepared statement) protocol enables you to send and receive date and time values (DATE, TIME, DATETIME, and TIMESTAMP), using the MYSQL_TIME structure. The members of this structure are described in Section 27.7.8, “C API Prepared Statement Data Structures”.

To send temporal data values, create a prepared statement using mysql_stmt_prepare(). Then, before calling mysql_stmt_execute() to execute the statement, use the following procedure to set up each temporal parameter:

  1. In the MYSQL_BIND structure associated with the data value, set the buffer_type member to the type that indicates what kind of temporal value you're sending. For DATE, TIME, DATETIME, or TIMESTAMP values, set buffer_type to MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, respectively.

  2. Set the buffer member of the MYSQL_BIND structure to the address of the MYSQL_TIME structure in which you pass the temporal value.

  3. Fill in the members of the MYSQL_TIME structure that are appropriate for the type of temporal value to pass.

Use mysql_stmt_bind_param() to bind the parameter data to the statement. Then you can call mysql_stmt_execute().

To retrieve temporal values, the procedure is similar, except that you set the buffer_type member to the type of value you expect to receive, and the buffer member to the address of a MYSQL_TIME structure into which the returned value should be placed. Use mysql_stmt_bind_result() to bind the buffers to the statement after calling mysql_stmt_execute() and before fetching the results.

Here is a simple example that inserts DATE, TIME, and TIMESTAMP data. The mysql variable is assumed to be a valid connection handler.

  MYSQL_TIME  ts;
  MYSQL_BIND  bind[3];
  MYSQL_STMT  *stmt;

  strmov(query, "INSERT INTO test_table(date_field, time_field, \
                               timestamp_field) VALUES(?,?,?");

  stmt = mysql_stmt_init(mysql);
  if (!stmt)
  {
    fprintf(stderr, " mysql_stmt_init(), out of memory\n");
    exit(0);
  }
  if (mysql_stmt_prepare(mysql, query, strlen(query)))
  {
    fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  }

  /* set up input buffers for all 3 parameters */
  bind[0].buffer_type= MYSQL_TYPE_DATE;
  bind[0].buffer= (char *)&ts;
  bind[0].is_null= 0;
  bind[0].length= 0;
  ...
  bind[1]= bind[2]= bind[0];
  ...

  mysql_stmt_bind_param(stmt, bind);

  /* supply the data to be sent in the ts structure */
  ts.year= 2002;
  ts.month= 02;
  ts.day= 03;

  ts.hour= 10;
  ts.minute= 45;
  ts.second= 20;

  mysql_stmt_execute(stmt);
  ..

27.7.17 C API Prepared CALL Statement Support

This section describes prepared-statement support in the C API for stored procedures executed using CALL statements:

Stored procedures executed using prepared CALL statements can be used in the following ways:

  • A stored procedure can produce any number of result sets. The number of columns and the data types of the columns need not be the same for all result sets.

  • The final values of OUT and INOUT parameters are available to the calling application after the procedure returns. These parameters are returned as an extra single-row result set following any result sets produced by the procedure itself. The row contains the values of the OUT and INOUT parameters in the order in which they are declared in the procedure parameter list.

    For information about the effect of unhandled conditions on procedure parameters, see Section 13.6.7.8, “Condition Handling and OUT or INOUT Parameters”.

The following discussion shows how to use these capabilities through the C API for prepared statements. To use prepared CALL statements through the PREPARE and EXECUTE statements, see Section 13.2.1, “CALL Statement”.

An application that executes a prepared CALL statement should use a loop that fetches a result and then invokes mysql_stmt_next_result() to determine whether there are more results. The results consist of any result sets produced by the stored procedure followed by a final status value that indicates whether the procedure terminated successfully.

If the procedure has OUT or INOUT parameters, the result set preceding the final status value contains their values. To determine whether a result set contains parameter values, test whether the SERVER_PS_OUT_PARAMS bit is set in the server_status member of the MYSQL connection handler:

mysql->server_status & SERVER_PS_OUT_PARAMS

The following example uses a prepared CALL statement to execute a stored procedure that produces multiple result sets and that provides parameter values back to the caller by means of OUT and INOUT parameters. The procedure takes parameters of all three types (IN, OUT, INOUT), displays their initial values, assigns new values, displays the updated values, and returns. The expected return information from the procedure therefore consists of multiple result sets and a final status:

  • One result set from a SELECT that displays the initial parameter values: 10, NULL, 30. (The OUT parameter is assigned a value by the caller, but this assignment is expected to be ineffective: OUT parameters are seen as NULL within a procedure until assigned a value within the procedure.)

  • One result set from a SELECT that displays the modified parameter values: 100, 200, 300.

  • One result set containing the final OUT and INOUT parameter values: 200, 300.

  • A final status packet.

The code to execute the procedure:

MYSQL_STMT *stmt;
MYSQL_BIND ps_params[3];  /* input parameter buffers */
int        int_data[3];   /* input/output values */
my_bool    is_null[3];    /* output value nullability */
int        status;

/* set up stored procedure */
status = mysql_query(mysql, "DROP PROCEDURE IF EXISTS p1");
test_error(mysql, status);

status = mysql_query(mysql,
  "CREATE PROCEDURE p1("
  "  IN p_in INT, "
  "  OUT p_out INT, "
  "  INOUT p_inout INT) "
  "BEGIN "
  "  SELECT p_in, p_out, p_inout; "
  "  SET p_in = 100, p_out = 200, p_inout = 300; "
  "  SELECT p_in, p_out, p_inout; "
  "END");
test_error(mysql, status);

/* initialize and prepare CALL statement with parameter placeholders */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  printf("Could not initialize statement\n");
  exit(1);
}
status = mysql_stmt_prepare(stmt, "CALL p1(?, ?, ?)", 16);
test_stmt_error(stmt, status);

/* initialize parameters: p_in, p_out, p_inout (all INT) */
memset(ps_params, 0, sizeof (ps_params));

ps_params[0].buffer_type = MYSQL_TYPE_LONG;
ps_params[0].buffer = (char *) &int_data[0];
ps_params[0].length = 0;
ps_params[0].is_null = 0;

ps_params[1].buffer_type = MYSQL_TYPE_LONG;
ps_params[1].buffer = (char *) &int_data[1];
ps_params[1].length = 0;
ps_params[1].is_null = 0;

ps_params[2].buffer_type = MYSQL_TYPE_LONG;
ps_params[2].buffer = (char *) &int_data[2];
ps_params[2].length = 0;
ps_params[2].is_null = 0;

/* bind parameters */
status = mysql_stmt_bind_param(stmt, ps_params);
test_stmt_error(stmt, status);

/* assign values to parameters and execute statement */
int_data[0]= 10;  /* p_in */
int_data[1]= 20;  /* p_out */
int_data[2]= 30;  /* p_inout */

status = mysql_stmt_execute(stmt);
test_stmt_error(stmt, status);

/* process results until there are no more */
do {
  int i;
  int num_fields;       /* number of columns in result */
  MYSQL_FIELD *fields;  /* for result set metadata */
  MYSQL_BIND *rs_bind;  /* for output buffers */

  /* the column count is > 0 if there is a result set */
  /* 0 if the result is only the final status packet */
  num_fields = mysql_stmt_field_count(stmt);

  if (num_fields > 0)
  {
    /* there is a result set to fetch */
    printf("Number of columns in result: %d\n", (int) num_fields);

    /* what kind of result set is this? */
    printf("Data: ");
    if(mysql->server_status & SERVER_PS_OUT_PARAMS)
      printf("this result set contains OUT/INOUT parameters\n");
    else
      printf("this result set is produced by the procedure\n");

    MYSQL_RES *rs_metadata = mysql_stmt_result_metadata(stmt);
    test_stmt_error(stmt, rs_metadata == NULL);

    fields = mysql_fetch_fields(rs_metadata);

    rs_bind = (MYSQL_BIND *) malloc(sizeof (MYSQL_BIND) * num_fields);
    if (!rs_bind)
    {
      printf("Cannot allocate output buffers\n");
      exit(1);
    }
    memset(rs_bind, 0, sizeof (MYSQL_BIND) * num_fields);

    /* set up and bind result set output buffers */
    for (i = 0; i < num_fields; ++i)
    {
      rs_bind[i].buffer_type = fields[i].type;
      rs_bind[i].is_null = &is_null[i];

      switch (fields[i].type)
      {
        case MYSQL_TYPE_LONG:
          rs_bind[i].buffer = (char *) &(int_data[i]);
          rs_bind[i].buffer_length = sizeof (int_data);
          break;

        default:
          fprintf(stderr, "ERROR: unexpected type: %d.\n", fields[i].type);
          exit(1);
      }
    }

    status = mysql_stmt_bind_result(stmt, rs_bind);
    test_stmt_error(stmt, status);

    /* fetch and display result set rows */
    while (1)
    {
      status = mysql_stmt_fetch(stmt);

      if (status == 1 || status == MYSQL_NO_DATA)
        break;

      for (i = 0; i < num_fields; ++i)
      {
        switch (rs_bind[i].buffer_type)
        {
          case MYSQL_TYPE_LONG:
            if (*rs_bind[i].is_null)
              printf(" val[%d] = NULL;", i);
            else
              printf(" val[%d] = %ld;",
                     i, (long) *((int *) rs_bind[i].buffer));
            break;

          default:
            printf("  unexpected type (%d)\n",
              rs_bind[i].buffer_type);
        }
      }
      printf("\n");
    }

    mysql_free_result(rs_metadata); /* free metadata */
    free(rs_bind);                  /* free output buffers */
  }
  else
  {
    /* no columns = final status packet */
    printf("End of procedure output\n");
  }

  /* more results? -1 = no, >0 = error, 0 = yes (keep looking) */
  status = mysql_stmt_next_result(stmt);
  if (status > 0)
    test_stmt_error(stmt, status);
} while (status == 0);

mysql_stmt_close(stmt);

Execution of the procedure should produce the following output:

Number of columns in result: 3
Data: this result set is produced by the procedure
 val[0] = 10; val[1] = NULL; val[2] = 30;
Number of columns in result: 3
Data: this result set is produced by the procedure
 val[0] = 100; val[1] = 200; val[2] = 300;
Number of columns in result: 2
Data: this result set contains OUT/INOUT parameters
 val[0] = 200; val[1] = 300;
End of procedure output

The code uses two utility routines, test_error() and test_stmt_error(), to check for errors and terminate after printing diagnostic information if an error occurred:

static void test_error(MYSQL *mysql, int status)
{
  if (status)
  {
    fprintf(stderr, "Error: %s (errno: %d)\n",
            mysql_error(mysql), mysql_errno(mysql));
    exit(1);
  }
}

static void test_stmt_error(MYSQL_STMT *stmt, int status)
{
  if (status)
  {
    fprintf(stderr, "Error: %s (errno: %d)\n",
            mysql_stmt_error(stmt), mysql_stmt_errno(stmt));
    exit(1);
  }
}

27.7.18 C API Prepared Statement Problems

Here follows a list of the currently known problems with prepared statements:

27.7.19 C API Automatic Reconnection Control

The MySQL client library can perform an automatic reconnection to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. If auto-reconnect is enabled, the library tries once to reconnect to the server and send the statement again.

Auto-reconnect is disabled by default.

If it is important for your application to know that the connection has been dropped (so that it can exit or take action to adjust for the loss of state information), be sure that auto-reconnect is disabled. To ensure this, call mysql_options() with the MYSQL_OPT_RECONNECT option:

my_bool reconnect = 0;
mysql_options(&mysql, MYSQL_OPT_RECONNECT, &reconnect);

If the connection has gone down, the effect of mysql_ping() depends on the auto-reconnect state. If auto-reconnect is enabled, mysql_ping() performs a reconnect. Otherwise, it returns an error.

Some client programs might provide the capability of controlling automatic reconnection. For example, mysql reconnects by default, but the --skip-reconnect option can be used to suppress this behavior.

If an automatic reconnection does occur (for example, as a result of calling mysql_ping()), there is no explicit indication of it. To check for reconnection, call mysql_thread_id() to get the original connection identifier before calling mysql_ping(), then call mysql_thread_id() again to see whether the identifier changed.

Automatic reconnection can be convenient because you need not implement your own reconnect code, but if a reconnection does occur, several aspects of the connection state are reset on the server side and your application will not be notified.

The connection-related state is affected as follows:

  • Any active transactions are rolled back and autocommit mode is reset.

  • All table locks are released.

  • All TEMPORARY tables are closed (and dropped).

  • Session system variables are reinitialized to the values of the corresponding global system variables, including system variables that are set implicitly by statements such as SET NAMES.

  • User variable settings are lost.

  • Prepared statements are released.

  • HANDLER variables are closed.

  • The value of LAST_INSERT_ID() is reset to 0.

  • Locks acquired with GET_LOCK() are released.

  • The association of the client with the Performance Schema threads table row that determines connection thread instrumentation is lost. If the client reconnects after a disconnect, the session is associated with a new row in the threads table and the thread monitoring state may be different. See Section 25.12.16.3, “The threads Table”.

If reconnection occurs, any SQL statement specified by calling mysql_options() with the MYSQL_INIT_COMMAND option is re-executed.

If the connection drops, it is possible that the session associated with the connection on the server side will still be running if the server has not yet detected that the client is no longer connected. In this case, any locks held by the original connection still belong to that session, so you may want to kill it by calling mysql_kill().

27.7.20 C API Common Issues

27.7.20.1 Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success

It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred:

  • There was a malloc() failure (for example, if the result set was too large).

  • The data could not be read (an error occurred on the connection).

  • The query returned no data (for example, it was an INSERT, UPDATE, or DELETE).

You can always check whether the statement should have produced a nonempty result by calling mysql_field_count(). If mysql_field_count() returns zero, the result is empty and the last query was a statement that does not return values (for example, an INSERT or a DELETE). If mysql_field_count() returns a nonzero value, the statement should have produced a nonempty result. See the description of the mysql_field_count() function for an example.

You can test for an error by calling mysql_error() or mysql_errno().

27.7.20.2 What Results You Can Get from a Query

In addition to the result set returned by a query, you can also get the following information:

27.7.20.3 How to Get the Unique ID for the Last Inserted Row

If you insert a record into a table that contains an AUTO_INCREMENT column, you can obtain the value stored into that column by calling the mysql_insert_id() function.

You can check from your C applications whether a value was stored in an AUTO_INCREMENT column by executing the following code (which assumes that you've checked that the statement succeeded). It determines whether the query was an INSERT with an AUTO_INCREMENT index:

if ((result = mysql_store_result(&mysql)) == 0 &&
    mysql_field_count(&mysql) == 0 &&
    mysql_insert_id(&mysql) != 0)
{
    used_id = mysql_insert_id(&mysql);
}

When a new AUTO_INCREMENT value has been generated, you can also obtain it by executing a SELECT LAST_INSERT_ID() statement with mysql_query() and retrieving the value from the result set returned by the statement.

When inserting multiple values, the last automatically incremented value is returned.

For LAST_INSERT_ID(), the most recently generated ID is maintained in the server on a per-connection basis. It is not changed by another client. It is not even changed if you update another AUTO_INCREMENT column with a nonmagic value (that is, a value that is not NULL and not 0). Using LAST_INSERT_ID() and AUTO_INCREMENT columns simultaneously from multiple clients is perfectly valid. Each client will receive the last inserted ID for the last statement that client executed.

If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:

INSERT INTO foo (auto,text)
    VALUES(NULL,'text');         # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
    VALUES(LAST_INSERT_ID(),'text');  # use ID in second table

mysql_insert_id() returns the value stored into an AUTO_INCREMENT column, whether that value is automatically generated by storing NULL or 0 or was specified as an explicit value. LAST_INSERT_ID() returns only automatically generated AUTO_INCREMENT values. If you store an explicit value other than NULL or 0, it does not affect the value returned by LAST_INSERT_ID().

For more information on obtaining the last ID in an AUTO_INCREMENT column:

27.8 MySQL PHP API

The MySQL PHP API manual is now published in standalone form, not as part of the MySQL Reference Manual. See MySQL and PHP.

27.9 MySQL Perl API

The Perl DBI module provides a generic interface for database access. You can write a DBI script that works with many different database engines without change. To use DBI with MySQL, install the following:

  1. The DBI module.

  2. The DBD::mysql module. This is the DataBase Driver (DBD) module for Perl.

  3. Optionally, the DBD module for any other type of database server you want to access.

Perl DBI is the recommended Perl interface. It replaces an older interface called mysqlperl, which should be considered obsolete.

These sections contain information about using Perl with MySQL and writing MySQL applications in Perl:

DBI information is available at the command line, online, or in printed form:

  • Once you have the DBI and DBD::mysql modules installed, you can get information about them at the command line with the perldoc command:

    shell> perldoc DBI
    shell> perldoc DBI::FAQ
    shell> perldoc DBD::mysql
    

    You can also use pod2man, pod2html, and so on to translate this information into other formats.

  • For online information about Perl DBI, visit the DBI website, http://dbi.perl.org/. That site hosts a general DBI mailing list.

  • For printed information, the official DBI book is Programming the Perl DBI (Alligator Descartes and Tim Bunce, O'Reilly & Associates, 2000). Information about the book is available at the DBI website, http://dbi.perl.org/.

27.10 MySQL Python API

MySQLdb is a third-party driver that provides MySQL support for Python, compliant with the Python DB API version 2.0. It can be found at http://sourceforge.net/projects/mysql-python/.

The new MySQL Connector/Python component provides an interface to the same Python API, and is built into the MySQL Server and supported by Oracle. See MySQL Connector/Python Developer Guide for details on the Connector, as well as coding guidelines for Python applications and sample Python code.

27.11 MySQL Ruby APIs

Two APIs are available for Ruby programmers developing MySQL applications:

For background and syntax information about the Ruby language, see Ruby Programming Language.

27.11.1 The MySQL/Ruby API

The MySQL/Ruby module provides access to MySQL databases using Ruby through libmysqlclient.

For information on installing the module, and the functions exposed, see MySQL/Ruby.

27.11.2 The Ruby/MySQL API

The Ruby/MySQL module provides access to MySQL databases using Ruby through a native driver interface using the MySQL network protocol.

For information on installing the module, and the functions exposed, see Ruby/MySQL.

27.12 MySQL Tcl API

MySQLtcl is a simple API for accessing a MySQL database server from the Tcl programming language. It can be found at http://www.xdobry.de/mysqltcl/.

27.13 MySQL Eiffel Wrapper

Eiffel MySQL is an interface to the MySQL database server using the Eiffel programming language, written by Michael Ravits. It can be found at http://efsa.sourceforge.net/archive/ravits/mysql.htm.