c++ - c++连接数据库

Question

在 php 中，我创建了一个打开到数据库的连接的配置文件，然后我在我的所有其他文件中使用该文件，以便也打开一个连接。但我似乎找不到用 C++ 做同样事情的方法。我可以连接到数据库，但我不能将它用作一个类，因为我在其中有一个 main() 并且我似乎无法在没有 main 的情况下使其工作。这是我的代码:

// Standard C++ includes
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

// Include the Connector/C++ headers
#include "cppconn/driver.h"
#include "cppconn/exception.h"
#include "cppconn/resultset.h"
#include "cppconn/statement.h"

// Link to the Connector/C++ library
#pragma comment(lib, "mysqlcppconn.lib")

// Specify our connection target and credentials
const string server   = "localhost";
const string username = "root";
const string password = "";

int main()
{
    sql::Driver     *driver; // Create a pointer to a MySQL driver object
        sql::Connection *dbConn; // Create a pointer to a database connection object
        sql::Statement  *stmt;   // Create a pointer to a Statement object to hold our SQL commands
        sql::ResultSet  *res;    // Create a pointer to a ResultSet object to hold the results of any queries we run

    // Try to get a driver to use to connect to our DBMS
    try
    {
        driver = get_driver_instance();
    }
    catch (sql::SQLException e)
    {
        cout << "Could not get a database driver. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }

    // Try to connect to the DBMS server
    try
    {
        dbConn = driver->connect(server, username, password);
    }
    catch (sql::SQLException e)
    {
        cout << "Could not connect to database. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }

    stmt = dbConn->createStatement();

    // Try to query the database
    try
    {
        stmt->execute("USE test");

        res = stmt->executeQuery("SELECT * FROM users");

    }
    catch (sql::SQLException e)
    {
        cout << "SQL error. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }


    sql::ResultSetMetaData *res_meta = res -> getMetaData();
    int columns = res_meta -> getColumnCount();

    while (res->next())
    {
        for (int i = 1; i <= columns; i++) {
                cout << res->getString(i) << " | " ;
                }
         cout << endl;
    }

    delete res;
    delete stmt;
    delete dbConn;
    return 0;
}

Answer 1

您需要创建一个类(例如class DBConnector)并在头文件中声明函数。例如，这段代码可以进入一个函数:

sql::Driver* DBConnector::GetDriverInstance()
{
try
    {
        m_driver = get_driver_instance();
    }
    catch (sql::SQLException e)
    {
        cout << "Could not get a database driver. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }
    return m_driver;
}

这里的sql::Driver *m_driver应该在头文件中声明为类的成员变量。在实际继续编写代码之前，您可能需要阅读更多关于类、成员函数和变量的内容。除此之外，您需要非常注意内存管理。我建议您阅读更多内容并使用智能指针，例如 std::shared_ptr。