sudo apt-get install libmysqlclient-dev

mysql> show databases;
+--------------------+
| Database      |
+--------------------+
| information_schema |
| chat_room     |
| mysql       |
| mysql_shiyan    |
| performance_schema |
| sys        |
+--------------------+
6 rows in set (0.00 sec)
mysql> use chat_room;
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_chat_room |
+---------------------+
| user_message    |
+---------------------+
1 row in set (0.00 sec)
mysql> select * from user_message;
+------+-------+--------+
| ID  | name | passwd |
+------+-------+--------+
|  1 | linux | linux |
|  2 | lyt  | lyt  |
+------+-------+--------+
2 rows in set (0.00 sec)

#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<mysql/mysql.h>

int main(void)
{
  char *sql;
  sql="SELECT * FROM user_message;";
  int res;//执行sql语句后的返回标志
  MYSQL_RES *res_ptr;//指向查询结果的指针
  MYSQL_FIELD *field;//字段结构指针
  MYSQL_ROW result_row;//按行返回查询信息
  int row,column;//查询返回的行数和列数
  MYSQL *conn;//一个数据库链接指针
  int i,j;

  //初始化连接句柄
  conn = mysql_init(NULL);

  if(conn == NULL) { //如果返回NULL说明初始化失败
    printf("mysql_init failed!\n");
    return EXIT_FAILURE;
  }

  //进行实际连接
  //参数　conn连接句柄，host　mysql所在的主机或地址,user用户名,passwd密码,database_name数据库名,后面的都是默认
  conn = mysql_real_connect(conn,"localhost","lyt","","chat_room",0,NULL,0);
  if (conn) {
    printf("Connection success!\n");
  } else {
    printf("Connection failed!\n");
  }
  mysql_query(conn,"set names gbk");//防止乱码。设置和数据库的编码一致就不会乱码

  res = mysql_query(conn,sql);//正确返回0
  if(res) {
    perror("my_query");
    mysql_close(conn);
    exit(0);
  } else{
    //把查询结果给res_ptr
    res_ptr = mysql_store_result(conn);
    //如果结果不为空,则输出
    if(res_ptr) {
      column = mysql_num_fields(res_ptr);
      row = mysql_num_rows(res_ptr);
      printf("查到%d行\n",row);
      //输出结果的字段名
      for(i = 0;field = mysql_fetch_field(res_ptr);i++) {
        printf("%10s",field->name);
      }
      puts("");
      //按行输出结果
      for(i = 1;i < row+1;i++){
        result_row = mysql_fetch_row(res_ptr);
        for(j = 0;j< column;j++) {
          printf("%10s",result_row[j]);
        }
        puts("");
      }
    }
  }
  //退出前关闭连接
  mysql_close(conn);

  return 0;
}

gcc -o mysql a.c -L/usr/lib/mysql -lmysqlclient
./mysql 
Connection success!
查到2行
    ID   name  passwd
     1   linux   linux
     2    lyt    lyt