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)
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