Question

我使用VS 2010 Professional在C ++中进行编程，但我遇到了这个问题：

如果程序启动且连接良好，则会加载＆＃34; gameactive＆＃34;循环，并显示播放器的高分。

但是当连接出错时，它会冻结并崩溃。我想显示一个错误，如＆＃34;错误连接到服务器＆＃34;并继续加载游戏。

我确实使用过这个教程： http://r3dux.org/2010/11/how-to-use-mysql-connectorc-to-connect-to-a-mysql-database-in-windows/

这是我的代码：

// Standad C++ includes
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
#include <string.h>

// Include the Connector/C++ headers
#include "cppconn/driver.h"
#include "cppconn/exception.h"
#include "cppconn/resultset.h"
#include "cppconn/statement.h"
#include <cgl\cgl.h>
#include <cgl\core.h>
#include <core\corefile.h>

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

// Specify our connection target and credentials
const string server   = "tcp://xxx.xxx.xxx.xxx:3306";
const string username = "xxxxxxx";
const string password = "XXxxXXxxXXxx";

char myoutput[1024];
char myoutput1[1024];
char myoutput2[1024];

s_font font;
s_bitmap bmp_background;

int connectsetup()
{
    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;
    }

    // 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;
    }

    stmt = dbConn->createStatement(); // Specify which connection our SQL statement should be executed on

    // Try to query the database
    try
    {
        stmt->execute("USE runner");              // Select which database to use. Notice that we use "execute" to perform a command.

        res = stmt->executeQuery("SELECT * FROM highscores"); // Perform a query and get the results. Notice that we use "executeQuery" to get results back
    }
    catch (sql::SQLException e)
    {
        cout << "SQL error. Error message: " << e.what() << endl;
    }

    // While there are still results (i.e. rows/records) in our result set...
    while (res->next())
    {
        // ...get each field we want and output it to the screen
        // Note: The first field/column in our result-set is field 1 (one) and -NOT- field 0 (zero)
        // Also, if we know the name of the field then we can also get it directly by name by using:
        // res->getString("TheNameOfTheField");
        //printf(myoutput,"%s %s %s",res->getString(1),res->getString(2),res->getString(3));
        strcpy(myoutput,res->getString(1).c_str());
        strcpy(myoutput1,res->getString(2).c_str());
        strcpy(myoutput2,res->getString(3).c_str());
    }

    // Clean up after ourselves
    delete res;
    delete stmt;
    delete dbConn;

    return 0;
}

void coremain()
{
    //Fullscreen, windowed of scaled?
    corefile_mountimage("res",MOUNT_DIR);
    CGL_InitVideo(1280, 720, CGL_VIDEO_NONE);
    CGL_SetTitle("CGL - Endless poepert");
    CGL_InitFont("font_heat.tga", &font);
    CGL_LoadBitmap("track1.tga",&bmp_background);
    connectsetup();
    int gameactive=1;

    int getal=atoi(myoutput);

    do {
        do {
            CGL_WaitRefresh();
            CGL_DrawBitmap(0,0,bmp_background); 
            CGL_DrawCenteredText(100,font, "%s: %d van %s score %s",myoutput,getal,myoutput1,myoutput2);
            int key,keytrig;
            CGL_GetKeys(&key,&keytrig);
            if (keytrig & CGL_INPUT_KEY_EXIT) exit(EXIT_SUCCESS);
            CGL_SwapBuffers(); 
        } while(gameactive);
        CGL_FlushGraphics();

    } while(1);
    CGL_CloseVideo();
}

Answer 1

问题似乎是您的connectSetup功能。您有try/catch个区块，但如果出现问题，您就无法执行任何操作。你只是继续前进，好像什么都没有错。

此外，这是学习智能指针的好时机。这里应该使用智能指针的原因是即使数据库连接成功也会出现问题（你有后续的try / catch块）。您希望确保清除已分配的任何内容，无论您何时何地发出return语句。

#include <memory>
#include <string>

std::string myoutput;
std::string myoutput1;
std::string myoutput2;

int connectsetup()
{
   sql::Driver* driver;
   std::unique_ptr<sql::Connection> dbConn;
   std::unique_ptr<sql::Statement> stmt;
   std::unique_ptr<sql::ResultSet> res;

   try
   {
        driver = get_driver_instance();
        dbConn.reset(driver->connect(server, username, password))
        stmt.reset(dbConn->createStatement());         
        stmt->execute("USE runner"); 
        res.reset(stmt->executeQuery("SELECT * FROM highscores")); // Perform a query 
        while (res->next())
        {
            myoutput = res->getString(1);
            myoutput1 = res->getString(2);
            myoutput2 = res->getString(3);
        }
    }
    catch (const sql::SQLException& e)
    {
        cout << "Something went wrong with the database stuff.  Here it is: " << e.what() << endl;
        return -1;
    }
    return 0;
}

此代码未编译，但我尝试提取您的原始代码正在执行的操作，并使用智能指针重写它。

如果任何这些语句失败，上面的代码将抛出异常。请注意，我们通过reference捕获异常，而不是按值捕获异常。另请注意，不需要delete，因为std::unique_ptr会自动执行此操作。

最后，不需要char数组 - 为什么要引入它们？它只会使你的函数的另一部分容易受到内存覆盖，即在res->next()循环中。

当MySQL服务器不可用时，为什么我的程序崩溃了

1 个答案: