Linux c 操作Mysql简单实例

在大型软件编程中，数据库是必不可少的，通常需要通过各种编程语言访问和操作数据库。本文介绍了在Linux 下使用C语言去操作Mysql数据库的方法。还有很重要的一点是： 在编程中，使用基础API操作数据库会比较复杂，不实用，软件开发者通常会在原有基础上抽象出一组使用更方便的API接口，本文也作了简单的抽象API（函数），如top_XX_XX()函数，仅供学习。

1. 首先在命令行通过SQL语句在mysql数据库中创建一个student表，并插入两条数据（1， zhangsan)和(2, lisi), 过程如下：

$mysql -h 127.0.0.1 -uroot -p

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| kamailio           |
| mysql              |
| opensips           |
| performance_schema |
| student            |
+--------------------+
6 rows in set (0.12 sec)

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
.....

mysql> create table student(id int(4) not null primary key auto_increment, name char(20) not null);
Query OK, 0 rows affected (0.52 sec)

mysql> desc student;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(4)   | NO   | PRI | NULL    | auto_increment |
| name  | char(20) | NO   |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.19 sec)

mysql> insert into student(id, name) values(1, "zhangsan");
Query OK, 1 row affected (0.07 sec)

mysql> select * from student;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
+----+----------+

mysql> insert into student(name) values("lisi");
Query OK, 1 row affected (0.09 sec)

mysql> select * from student;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
|  2 | lisi     |
+----+----------+
2 rows in set (0.00 sec)

2. 实例

Linux C mysql 在线API文档:

http://www.yesky.com/imagesnew/software/mysql/manual_Clients.html

在Linux下使用C语言访问Mysql,需要安装额外的开发包：

sudo apt-get install libmysqlclient15-dev

mysql_test.c：
#include <mysql/mysql.h>
#include <stdio.h>
#include <stdlib.h>

#define debug() \
    printf("%s, %d\n", __FUNCTION__, __LINE__)

#define MAX_QUERY_CMD_LEN 1024

MYSQL *conn = NULL;
char table_name[] = "student";

void top_log(const char *log)
{
    printf("%s\n", log);
}


MYSQL_RES *top_query_database(MYSQL *conn)
{
    MYSQL_RES *res = NULL;

    if (!conn) {
        top_log("param is NULL");
        return NULL;
    }

    if (mysql_query(conn, "show databases")) 
    {
        top_log(mysql_error(conn));
        return NULL;
    }

    res = mysql_store_result(conn);
    if (!res) {
        top_log(mysql_error(conn));
        return NULL;
    }

    return res;
}

MYSQL_RES *top_query_table(MYSQL *conn)
{
    MYSQL_RES *res = NULL;

    if (!conn) {
        top_log("param is NULL");
        return NULL;
    }

    if (mysql_query(conn, "show tables")) 
    {
        top_log(mysql_error(conn));
        return NULL;
    }

    res = mysql_store_result(conn);
    if (!res) {
        top_log(mysql_error(conn));
        return NULL;
    }

    return res;
}

MYSQL_RES *top_insert_into_table(MYSQL *conn, char *table, char *fields, char *values)
{
    MYSQL_RES *res = NULL;
    int len = -1;
    char sql_cmd[MAX_QUERY_CMD_LEN];

    if (!conn || !table || !fields || !values) {
        top_log("param is NULL");
        return NULL;
    }

	if (fields) {
    	len = snprintf(sql_cmd, MAX_QUERY_CMD_LEN, "insert into %s%s values%s",
				 table, fields, values);
	} else {
    	len = snprintf(sql_cmd, MAX_QUERY_CMD_LEN, "insert into %s values%s",
				 table, values);
	}

    printf("sql_cmd: %s, len: %d\n", sql_cmd, len);

    if (mysql_query(conn, sql_cmd)) 
    {
        top_log(mysql_error(conn));
        return NULL;
    }

    res = mysql_store_result(conn);

    if (!res) {
        top_log(mysql_error(conn));
        return NULL;
    }
    return res;
}

MYSQL_RES *top_select_from_table(MYSQL *conn, char *table, char *condition)
{
    MYSQL_RES *res = NULL;
    int len = -1;
    char sql_cmd[MAX_QUERY_CMD_LEN];

    if (!conn || !table) {
        top_log("param is NULL");
        return NULL;
    }

    len = snprintf(sql_cmd, MAX_QUERY_CMD_LEN, "select * from %s", table);

    printf("sql_cmd: %s, len: %d\n", sql_cmd, len);

    if (condition) {
        snprintf(sql_cmd + len, MAX_QUERY_CMD_LEN, " where %s", condition);
    }

    printf("sql_cmd: %s, len: %d\n", sql_cmd, len);
    if (mysql_query(conn, sql_cmd)) 
    {
        top_log(mysql_error(conn));
        return NULL;
    }

    res = mysql_store_result(conn);

    if (!res) {
        top_log(mysql_error(conn));
        return NULL;
    }
    return res;
}

int main() 
{
    MYSQL_RES *res;
    MYSQL_ROW row;
    int ret = -1;
    int i, j;
    char server[] = "localhost";
    char user[] = "root";
    char password[] = "hello";
    char database[] = "mysql";
    
    conn = mysql_init(NULL);
    
    if (!mysql_real_connect(conn, server,user, password, database, 0, NULL, 0)) 
    {
        fprintf(stderr, "%s\n", mysql_error(conn));
        exit(1);
    }
 
    res = top_query_database(conn);
    if (!res) {
        printf("error\n");
        exit(1);
    }

    printf("MySQL num_rows: %lu, num_fileds: %d\n",
                    (unsigned long)mysql_num_rows(res), mysql_num_fields(res));
    
    while ((row = mysql_fetch_row(res)) != NULL)
    {
        printf("%s \n", row[0]);
    }

    /* select db*/
    ret = mysql_select_db(conn, "mysql");
    if (ret) {
        printf("select db error: %s\n", mysql_error(conn));
    }

    res = top_query_table(conn);
    if (!res) {
        printf("error\n");
        exit(1);
    }
    printf("MySQL num_rows: %lu, num_fileds: %d\n",
                    (unsigned long)mysql_num_rows(res), mysql_num_fields(res));
    while ((row = mysql_fetch_row(res)) != NULL)
    {
		// print all tables in mysql database
        printf("%s \n", row[0]);
    }

    mysql_free_result(res);

	top_insert_into_table(conn, table_name, "(name)", "(\"wangwu\")");

    res = top_select_from_table(conn, table_name, NULL); 
    printf("MySQL num_rows: %lu, num_fileds: %d\n",
                    (unsigned long)mysql_num_rows(res), mysql_num_fields(res));
    
    int field_count = res->field_count;
    printf("field_count: %d\n", field_count);
    while ((row = mysql_fetch_row(res)) != NULL)
    {
        for(i = 0; i < field_count; i++) {
            printf("%s\n", row[i]);
        }
    }
    mysql_free_result(res);
    mysql_close(conn);
    
    return 0;
}

Makefile:
CFLAGS=-g
all:
	gcc mysql_test.c -o a.out -lmysqlclient -g

结果：

$ ./a.out 
MySQL num_rows: 6, num_fileds: 1
information_schema 
kamailio 
mysql 
opensips 
performance_schema 
student 
MySQL num_rows: 25, num_fileds: 1
columns_priv 
db 
event 
func 
general_log 
help_category 
help_keyword 
help_relation 
help_topic 
host 
ndb_binlog_index 
plugin 
proc 
procs_priv 
proxies_priv 
servers 
slow_log 
student 
tables_priv 
time_zone 
time_zone_leap_second 
time_zone_name 
time_zone_transition 
time_zone_transition_type 
user 
sql_cmd: insert into student(name) values("wangwu"), len: 42


sql_cmd: select * from student, len: 21
sql_cmd: select * from student, len: 21
MySQL num_rows: 3, num_fileds: 2
field_count: 2
1
zhangsan
2
lisi
3
wangwu