MySQL入门之C语言操作MySQL

基本概念

C APIs包含在mysqlclient库文件当中，与MySQL的源代码一块发行，用于连接到数据库和执行数据库查询。

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <dlfcn.h> #include <mysql/mysql.h> int main() { int ret = 0; MYSQL mysql; MYSQL *con = NULL; con = mysql_init(&mysql); if (con == NULL) { ret = mysql_errno(&mysql); printf("func mysql_init() err :%d\n", ret); return ret; } //连接mysql服务器 //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) ; con = mysql_real_connect(&mysql, "localhost", "root", "123456", "mydb2", 0, NULL, 0 ); if (con == NULL) { ret = mysql_errno(&mysql); printf("func mysql_real_connect() err :%d\n", ret); return ret; } else { printf("func mysql_real_connect() ok\n"); } mysql_close(&mysql); return ret; }

编程步骤

1 通过调用mysql_library_init(),初始化MYSQL库 2 通过调用mysql_init()初始化连接处理程序，并通过调用mysql_real_connect()连接到服务器 3 发出SQL语句并处理其结果 4 通过调用mysql_close()，关闭与MYSQL服务器的连接 5 通过调用mysql_library_end()，结束MYSQL库的使用

编译需要注意的问题

问题1： [mysql01@localhost dm01]$ gcc -o dm11_hello dm11_hello.c -I/usr/include/ -L/usr/lib64/mysql/ -lmysqlclient /usr/lib64/mysql//libmysqlclient.a(net_serv.cc.o):(.data.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to __gxx_personality_v0' /usr/lib64/mysql//libmysqlclient.a(password.c.o): In functionscramble_323’:

需要用到c++的动态库，在编译选项中添加-lstdc++选项

问题2 /usr/lib64/mysql//libmysqlclient.a(dso_dlfcn.o): In function dlfcn_globallookup': dso_dlfcn.c:(.text+0x31): undefined reference todlopen’ dso_dlfcn.c:(.text+0x44): undefined reference to dlsym' dso_dlfcn.c:(.text+0x4f): undefined reference todlclose’ /usr/lib64/mysql//libmysqlclient.a(dso_dlfcn.o): In function dlfcn_pathbyaddr': dso_dlfcn.c:(.text+0xa0): undefined reference todladdr’ dso_dlfcn.c:(.text+0x101): undefined reference to dlerror' /usr/lib64/mysql//libmysqlclient.a(dso_dlfcn.o): In functiondlfcn_bind_func’: dso_dlfcn.c:(.text+0x464): undefined reference to `dlsym’

回调函数的正反向调用，需要使用到dl函数库，在编译选项中添加-ldl选项

问题3

thread_mutex_trylock’ /usr/lib64/mysql//libmysqlclient.a(my_thr_init.c.o): In function my_thread_global_end': /pb2/build/sb_0-12734909-1406113305.48/rpm/BUILD/mysqlcom-pro-5.6.20/mysqlcom-pro-5.6.20/mysys/my_thr_init.c:214: undefined reference topthread_key_delete’ /pb2/build/sb_0-12734909-1406113305.48/rpm/BUILD/mysqlcom-pro-5.6.20/mysqlcom-pro-5.6.20/mysys/my_thr_init.c:217: undefined reference to pthread_mutexattr_destroy' /pb2/build/sb_0-12734909-1406113305.48/rpm/BUILD/mysqlcom-pro-5.6.20/mysqlcom-pro-5.6.20/mysys/my_thr_init.c:220: undefined reference topthread_mutexattr_destroy’

MySQL的动态库用到多线程，所以编译选项中添加-lpthread选项

4.问题4

[mysql01@localhost dm01]$ gcc -o dm11_hello dm11_hello.c -I/usr/include/ -L/usr/lib64/mysql/ -lmysqlclient -ldl -lstdc++ -lpthread /usr/lib64/mysql//libmysqlclient.a(my_getsystime.c.o): In function my_getsystime': /pb2/build/sb_0-12734909-1406113305.48/rpm/BUILD/mysqlcom-pro-5.6.20/mysqlcom-pro-5.6.20/mysys/my_getsystime.c:44: undefined reference toclock_gettime’ collect2: ld 返回 1 [mysql01@localhost dm01]$

缺少运行时动态库以及数学库，添加-lm以及-lrt选项

完整的gcc编译命令：

gcc -o hello hello.c -I/usr/include/mysql/ -L/usr/lib/i386-linux-gnu/ -lmysqlclient -lm -ldl -lstdc++ -lpthread -lrt

一般Makefile编写

.PHONY:clean all CC=gcc CFLAGS=-Wall -g LFLAGS=-L/usr/lib/i386-linux-gnu/ -lmysqlclient -ldl -lpthread -lm -lrt -lstdc++ BIN=hello all:$(BIN) %.o:%.c $(CC) $(CFLAGS) -c $< -o $@ hello:hello.o $(CC) $(CFLAGS) $^ $(LFLAGS) -o $@ clean: rm -f *.o $(BIN)