【MySQL】使用C/C++连接MySQL数据库

本文目的：使用MySQL提供的CAPI完成对数据库的操作

验证

#include <iostream>
#include <mysql/mysql.h>int main()
{std::cout<<"mysql cilent version: "<<mysql_get_client_info()<<std::endl;return 0;
}

注意：使用mysqlclient库需要指明库的位置-L和库的名称-l

[wmh@pDaD Test]$ g++ test.cc -o  test -L/lib64/mysql -lmysqlclient
[wmh@pDaD Test]$ ./test
mysql cilent version: 5.7.42

使用

MySQL-5.7API接口介绍

#include <iostream>
#include <mysql/mysql.h>
#include <string>
#include <unistd.h>
const std::string host="127.0.0.1";
const std::string user = "connection";
const std::string passwd="123456";
const std::string db="scott";
const unsigned int port = 3306;
int main()
{MYSQL* mysql = mysql_init(nullptr);//初始化MySQL句柄if(nullptr == mysql){std::cerr<<"init MySQL error"<<std::endl;return 1;}if(mysql_real_connect(mysql,host.c_str(),user.c_str(),passwd.c_str(),db.c_str(),port,nullptr,0) == nullptr)//连接MySQL数据库{std::cerr<<"connect MySQL error"<<std::endl;return 2;}mysql_set_character_set(mysql,"utf8");//设置字符集编码std::string sql="update user set age='60' where id=3";int n = mysql_query(mysql,sql.c_str());//下发命令if(n==0) std::cout<<sql<<"success"<<std::endl;else std::cout<<sql<<"failed"<<std::endl;mysql_close(mysql);return 0;
}

mysql> select* from user;
+----+-----+-----------+
| id | age | name      |
+----+-----+-----------+
|  1 |  28 | 赵志敬    |
|  3 |  18 | 杨过      |
|  4 |  16 | 小龙女    |
+----+-----+-----------+mysql> select* from user;
+----+-----+-----------+
| id | age | name      |
+----+-----+-----------+
|  1 |  28 | 赵志敬    |
|  3 |  60 | 杨过      |
|  4 |  16 | 小龙女    |
+----+-----+-----------+

select特殊点

sql执行完以后，如果是查询语句，我们要能看到数据显示出来，那么就需要mysql_store_result这个函数来保存结果到本地

MYSQL_RES *mysql_store_result(MYSQL *mysql);

获取结果行数mysql_num_rows

my_ulonglong mysql_num_rows(MYSQL_RES *res);

获取结果列数mysql_num_fields

unsigned int mysql_num_fields(MYSQL_RES *res);

以列为单位获取列属性mysql_fetch_fields

MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *res);

typedef struct st_mysql_field {char *name;                 /* Name of column */char *org_name;             /* Original column name, if an alias */char *table;                /* Table of column if column was a field */char *org_table;            /* Org table name, if table was an alias */char *db;                   /* Database for table */char *catalog;	      /* Catalog for table */char *def;                  /* Default value (set by mysql_list_fields) */unsigned long length;       /* Width of column (create length) */unsigned long max_length;   /* Max width for selected set */unsigned int name_length;unsigned int org_name_length;unsigned int table_length;unsigned int org_table_length;unsigned int db_length;unsigned int catalog_length;unsigned int def_length;unsigned int flags;         /* Div flags */unsigned int decimals;      /* Number of decimals in field */unsigned int charsetnr;     /* Character set */enum enum_field_types type; /* Type of field. See mysql_com.h for types */void *extension;
} MYSQL_FIELD;

以行为单位获取结果内容mysql_fetch_row

MYSQL_ROW mysql_fetch_row(MYSQL_RES *result);

MYSQL_ROW其实就是char **.当成一个二维数组

释放结果集内存

void mysql_free_result(MYSQL_RES *result)

调用mysql_store_result返回结构体，这个函数malloc了一片内存空间来存储查询过来的数据，需要free掉

整体示例

#include <iostream>
#include <mysql/mysql.h>
#include <string>
#include <unistd.h>
const std::string host = "127.0.0.1";
const std::string user = "connection";
const std::string passwd = "123456";
const std::string db = "scott";
const unsigned int port = 3306;
int main()
{MYSQL *mysql = mysql_init(nullptr); // 初始化MySQL句柄if (nullptr == mysql){std::cerr << "init MySQL error" << std::endl;return 1;}if (mysql_real_connect(mysql, host.c_str(), user.c_str(), passwd.c_str(), db.c_str(), port, nullptr, 0) == nullptr) // 连接MySQL数据库{std::cerr << "connect MySQL error" << std::endl;return 2;}mysql_set_character_set(mysql, "utf8"); // 设置字符集编码// std::string sql="update user set age='60' where id=3";std::string sql = "select * from user";int n = mysql_query(mysql, sql.c_str()); // 下发命令if (n == 0)std::cout << sql << "success" << std::endl;elsestd::cout << sql << "failed" << std::endl;// 保存结果集转储到res中MYSQL_RES *res = mysql_store_result(mysql);if (res == nullptr){std::cerr << "mysql_store_result_error" << std::endl;}int rows = mysql_num_rows(res);     // 获取行数int fields = mysql_num_fields(res); // 获取列数std::cout << "行: " << rows << std::endl;std::cout << "列：" << fields << std::endl;// 获取列属性MYSQL_FIELD *fields_array = mysql_fetch_fields(res);for (int i = 0; i < fields; ++i){std::cout << fields_array[i].name << "\t"; // 打印列名}std::cout << std::endl;for (int i = 0; i < rows; i++){//row可以认为是一个char** 指针MYSQL_ROW row = mysql_fetch_row(res);//以行为单位获取记录for (int j = 0; j < fields; ++j){std::cout << row[j] << "\t";}std::cout << "\n";}std::cout << fields_array[0].db << " " << fields_array[0].table << std::endl;mysql_free_result(res);//释放结果集mysql_close(mysql);//关闭MYSQL句柄return 0;
}