Connect MySQL server using C program API under Linux

kevinhu

The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.
Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.
RequirementsMake sure you have development environment installed such as gcc, mysql development package etc. Following is the list summarize the list of packages to compile program:

• mysql: MySQL client programs and shared library
• mysqlclient:  Backlevel MySQL shared libraries (old libs)
• mysql-devel: Files for development of MySQL applications (a must have)
• mysql-server: Mysql server itself
• gcc, make and other development libs: GNU C compiler
  

Sample C ProgramFollowing instructions should work on any Linux distro or UNIX computer. Here is the small program that connects to mysql server and list tables from mysql database.(download link):
/* Simple C program that connects to MySQL Database server*/#include <mysql.h>#include <stdio.h>main() {   MYSQL *conn;   MYSQL_RES *res;   MYSQL_ROW row;   char *server = "localhost";   char *user = "root";   char *password = "PASSWORD"; /* set me first */   char *database = "mysql";   conn = mysql_init(NULL);   /* Connect to database */   if (!mysql_real_connect(conn, server,         user, password, database, 0, NULL, 0)) {      fprintf(stderr, "%s\n", mysql_error(conn));      exit(1);   }   /* send SQL query */   if (mysql_query(conn, "show tables")) {      fprintf(stderr, "%s\n", mysql_error(conn));      exit(1);   }   res = mysql_use_result(conn);   /* output table name */   printf("MySQL Tables in mysql database:\n");   while ((row = mysql_fetch_row(res)) != NULL)      printf("%s \n", row[0]);   /* close connection */   mysql_free_result(res);   mysql_close(conn);}How do I compile and link program against MySQL libs?MySQL comes with a special script called mysql_config. It provides you with useful information for compiling your MySQL client and connecting it to MySQL database server. You need to use following two options.
Pass --libs option - Libraries and options required to link with the MySQL client library.
$ mysql_config --libs
Output:
-L/usr/lib64/mysql -lmysqlclient -lz -lcrypt -lnsl -lm -L/usr/lib64 -lssl -lcryptoPass --cflags option -  Compiler flags to find include files and critical compiler flags and defines used when compiling the libmysqlclient library.
$ mysql_config --cflags
Output:
-I/usr/include/mysql -g -pipe -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasingYou need to pass above option to GNU C compiler i.e. gcc. So to compile above program, enter:
$ gcc  -o output-file $(mysql_config --cflags) mysql-c-api.c $(mysql_config --libs)
Now execute program:
$ ./output-file
Output:
MySQL Tables in mysql database:columns_privdbfunchelp_categoryhelp_keywordhelp_relationhelp_topichosttables_privtime_zonetime_zone_leap_secondtime_zone_nametime_zone_transitiontime_zone_transition_typeuser

blackjack

编译过程中出现错误时的原因是因为编译器找不到mysql_init,mysql_close等的具体实现.虽然我们包括了正确的头文件,但是我们在编译的时候还是要连接确定的库.对于一些常用的函数的实现,gcc编译器会自动去连接一些常用库,这样我们就没有必要自己去指定了,如:printf函数.在本程序中要通过-L选项包含库文件的路径:
gcc -o conn conn.c -L /usr/local/mysql/lib/*.a -lz

或者：

命令行后加入 -lmysqlclient
例如对mysqlconn.c编译
gcc mysqlconn.c -o conn -l mysqlclient
编译即可成功

blackjack

MySQL C API programming tutorial