C++ MySQL 常用接口（基于 MySQL Connector/C++）

C++ MySQL 常用接口（基于 MySQL Connector/C++）

1. 数据库连接

接口：

sql::mysql::MySQL_Driver *driver;
sql::Connection *con;

作用：

用于创建 MySQL 连接对象。

示例：

driver = sql::mysql::get_mysql_driver_instance();
con = driver->connect("tcp://127.0.0.1:3306", "user", "password");

释放资源：

delete con;

---

2. 选择数据库

接口：

con->setSchema("database_name");

作用：

指定要操作的数据库。

示例：

con->setSchema("test_db");

---

3. 创建 SQL 语句对象

接口：

sql::Statement *stmt;
stmt = con->createStatement();

作用：

创建一个 SQL 语句执行对象。

示例：

stmt = con->createStatement();
stmt->execute("CREATE TABLE IF NOT EXISTS users (id INT, name VARCHAR(50))");
delete stmt;

---

4. 执行 SQL 语句

接口：

stmt->execute("SQL语句");
stmt->executeQuery("SQL查询语句");
stmt->executeUpdate("SQL更新语句");

作用：

• execute() 用于执行不返回结果集的 SQL 语句（如 CREATE TABLE）。
• executeQuery() 用于执行 SELECT 查询，返回 ResultSet 结果集。
• executeUpdate() 用于 INSERT、UPDATE、DELETE，返回影响的行数。

示例：

stmt = con->createStatement();
stmt->execute("INSERT INTO users (id, name) VALUES (1, 'Tom')");
sql::ResultSet *res = stmt->executeQuery("SELECT * FROM users");
int rows = stmt->executeUpdate("UPDATE users SET name='Jerry' WHERE id=1");

delete res;
delete stmt;

---

5. 获取查询结果

接口：

sql::ResultSet *res;
res->next();
res->getInt("column_name");
res->getString("column_name");

作用：

获取查询结果，并读取列值。

示例：

sql::ResultSet *res = stmt->executeQuery("SELECT * FROM users");
while (res->next()) {
    std::cout << "ID: " << res->getInt("id") << ", Name: " << res->getString("name") << std::endl;
}
delete res;

---

6. 使用预处理语句

接口：

sql::PreparedStatement *pstmt;
pstmt = con->prepareStatement("SQL语句");
pstmt->setInt(参数索引, 整数值);
pstmt->setString(参数索引, 字符串值);
pstmt->execute();
pstmt->executeQuery();
pstmt->executeUpdate();

作用：

• prepareStatement() 预编译 SQL，提高执行效率并防止 SQL 注入。
• setInt() / setString() 设置 SQL 语句中的参数值。

示例：

sql::PreparedStatement *pstmt = con->prepareStatement("INSERT INTO users (id, name) VALUES (?, ?)");
pstmt->setInt(1, 2);
pstmt->setString(2, "Alice");
pstmt->executeUpdate();
delete pstmt;

---

7. 事务处理

自动提交（Auto Commit）

MySQL 默认启用 Auto Commit ，每条 INSERT、UPDATE、DELETE 语句都会 立即生效，即使程序崩溃，数据也已经修改了。

示例（默认自动提交）

sql::Statement *stmt = con->createStatement();
stmt->execute("UPDATE accounts SET balance = balance - 100 WHERE id = 1");
delete stmt;  // 即使程序崩溃，数据库的修改依然有效

手动事务（关闭自动提交）

如果希望多个 SQL 语句 全部成功或全部失败 ，需要 关闭自动提交 并手动 COMMIT 或 ROLLBACK。

接口：

con->setAutoCommit(false);
con->commit();
con->rollback();

作用：

• setAutoCommit(false)：关闭自动提交，进入事务模式。
• commit()：提交事务，所有 SQL 语句的更改生效。
• rollback()：回滚事务，撤销所有未提交的更改。

示例（手动控制事务）

try {
    con->setAutoCommit(false); // 关闭自动提交，开启事务模式

    sql::PreparedStatement *pstmt = con->prepareStatement("UPDATE accounts SET balance = balance - ? WHERE id = ?");
    pstmt->setDouble(1, 100.0);
    pstmt->setInt(2, 1);
    pstmt->executeUpdate();
    delete pstmt;

    pstmt = con->prepareStatement("UPDATE accounts SET balance = balance + ? WHERE id = ?");
    pstmt->setDouble(1, 100.0);
    pstmt->setInt(2, 2);
    pstmt->executeUpdate();
    delete pstmt;

    con->commit();  // **手动提交事务，所有修改一起生效**
} catch (sql::SQLException &e) {
    con->rollback();  // **出错时回滚，保证数据一致性**
    std::cerr << "Transaction failed: " << e.what() << std::endl;
}

事务的使用场景

适用于需要保证 数据一致性 的情况：

• 银行转账（A 账户扣钱，B 账户加钱，必须同时成功）
• 库存管理（购买商品时，需要同时更新库存和订单信息）
• 订单处理（下单时，必须同时修改多个表的数据）

总结

• MySQL 默认 Auto Commit = true，每条 SQL 语句都会立即提交。
• 关闭 Auto Commit 后，可以 手动提交或回滚，确保数据一致性。
• 使用 commit() 确保更改生效，使用 rollback() 处理失败情况。

---

8. 关闭连接

接口：

delete res;
delete stmt;
delete pstmt;
delete con;

作用：

释放资源，避免内存泄漏。

示例：

delete res;
delete stmt;
delete pstmt;
delete con;

---

总结

类别	接口	作用
数据库连接	sql::mysql::MySQL_Driver *driver; sql::Connection *con; driver = sql::mysql::get_mysql_driver_instance(); con = driver->connect(...);	连接 MySQL 数据库
选择数据库	con->setSchema("database_name");	选择数据库
执行 SQL	stmt->execute("SQL语句"); stmt->executeQuery("SQL查询语句"); stmt->executeUpdate("SQL更新语句");	执行 SQL 语句
获取查询结果	res->next(); res->getInt("column_name"); res->getString("column_name");	获取查询结果
预处理语句	pstmt = con->prepareStatement("SQL语句"); pstmt->setInt(1, value); pstmt->setString(2, "value"); pstmt->executeUpdate();	预编译 SQL，防止 SQL 注入
事务管理	con->setAutoCommit(false); con->commit(); con->rollback();	控制事务提交和回滚
释放资源	delete res; delete stmt; delete pstmt; delete con;	释放内存，避免泄漏

代码示例

/* Copyright 2008, 2010, Oracle and/or its affiliates.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.

There are special exceptions to the terms and conditions of the GPL
as it is applied to this software. View the full text of the
exception in file EXCEPTIONS-CONNECTOR-C++ in the directory of this
software distribution.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

/* Standard C++ includes */
#include <stdlib.h>
#include <iostream>

/*
  Include directly the different
  headers from cppconn/ and mysql_driver.h + mysql_util.h
  (and mysql_connection.h). This will reduce your build time!
*/
#include "mysql_connection.h"

#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/prepared_statement.h>

using namespace std;

int main(void)
{
cout << endl;
cout << "Let's have MySQL count from 10 to 1..." << endl;

try {
  sql::Driver *driver;
  sql::Connection *con;
  sql::Statement *stmt;
  sql::ResultSet *res;
  sql::PreparedStatement *pstmt;

  /* Create a connection */
  driver = get_driver_instance();
  con = driver->connect("tcp://127.0.0.1:3306", "root", "root");
  /* Connect to the MySQL test database */
  con->setSchema("test");

  stmt = con->createStatement();
  stmt->execute("DROP TABLE IF EXISTS test");
  stmt->execute("CREATE TABLE test(id INT)");
  delete stmt;

  /* '?' is the supported placeholder syntax */
  pstmt = con->prepareStatement("INSERT INTO test(id) VALUES (?)");
  for (int i = 1; i <= 10; i++) {
    pstmt->setInt(1, i);
    pstmt->executeUpdate();
  }
  delete pstmt;

  /* Select in ascending order */
  pstmt = con->prepareStatement("SELECT id FROM test ORDER BY id ASC");
  res = pstmt->executeQuery();

  /* Fetch in reverse = descending order! */
  res->afterLast();
  while (res->previous())
    cout << "\t... MySQL counts: " << res->getInt("id") << endl;
  delete res;

  delete pstmt;
  delete con;

} catch (sql::SQLException &e) {
  cout << "# ERR: SQLException in " << __FILE__;
  cout << "(" << __FUNCTION__ << ") on line " >>
     << __LINE__ << endl;
  cout << "# ERR: " << e.what();
  cout << " (MySQL error code: " << e.getErrorCode();
  cout << ", SQLState: " << e.getSQLState() << >>
     " )" << endl;
}

cout << endl;

return EXIT_SUCCESS;
}