(SDL 渲染问题)C++ 引发异常:读取访问冲突.这是无效的

Question

每当我运行程序时，我都会在两行单独的代码上抛出异常，如果我将其中一行注释出来，问题会跳转到另一行，但两者都引用相同的变量。

游戏屏幕管理器.cpp：

#pragma once
#include <SDL.h>
#include "Commons.h"
#include "GameScreenManager.h"
#include "GameScreenLevel1.h"
#include "GameScreen.h"
GameScreenManager::GameScreenManager(SDL_Renderer* renderer, SCREENS startScreen)
{
    SDL_Renderer* mRenderer;
    mRenderer = NULL;
    ChangeScreen(startScreen);
}
GameScreenManager::~GameScreenManager()
{
    mRenderer = NULL;
    delete mCurrentScreen;
    mCurrentScreen = NULL;
}
void GameScreenManager::Render()
{
    mCurrentScreen->Render();
}
void GameScreenManager::update(float deltaTime, SDL_Event e)
{
    mCurrentScreen->Update(deltaTime, e);
}
void GameScreenManager::ChangeScreen(SCREENS newScreen)
{
    //Clear up the old screen
    if (mCurrentScreen != NULL)
    {
        delete mCurrentScreen;
    }
    GameScreenLevel1* tempScreen;

    switch (newScreen)
    {
    case SCREEN_INTRO:
        break;
    case SCREEN_MENU:
        break;
    case SCREEN_LEVEL1:
        tempScreen = new GameScreenLevel1(mRenderer);
        mCurrentScreen = (GameScreen*)tempScreen;
        tempScreen = NULL;
        break;
    case SCREEN_LEVEL2:
        break;
    case SCREEN_GAMEOVER:
        break;
    case SCREEN_HIGHSCORES:
        break;
    default:
            break;
    }
}

GameScreenManager.h：

#pragma once
#ifndef _GAMESCREENMANAGER_H
#define _GAMESCREENMANAGER_H
#include <SDL.h>
#include "Commons.h"
class GameScreen;
class GameScreenManager
{
    private:
        SDL_Renderer*    mRenderer;
        GameScreen*      mCurrentScreen;
    public:
        GameScreenManager(SDL_Renderer* renderer, SCREENS startScreen);
        ~GameScreenManager();
        void Render();
        void update(float deltaTime, SDL_Event e);
        void ChangeScreen(SCREENS newScreen);
};
#endif //_GAMESCREENMANAGER_H

目前问题出现在第 24 行;

    mCurrentScreen->Render();

但是，如果我注释掉该行，则它出现在第 29 行：

    mCurrentScreen->Update(deltaTime, e);

"引发未处理的异常：读取访问冲突。这是无效的。发生">

Answer 1

显然，当你调用 Render(( 或 update(( 时，mCurrentScreen 字段是空的。通过检查 mCurrentScreen 的空来保护呼叫：

void GameScreenManager::Render()
{
    if (mCurrentScreen != NULL)
        mCurrentScreen->Render();
}
void GameScreenManager::update(float deltaTime, SDL_Event e)
{
    if (mCurrentScreen != NULL)
        mCurrentScreen->Update(deltaTime, e);
}

或者确保在调用 Render(( 或 Update(( 之前设置了 mCurrentScreen。

Answer 2

碰

巧的是，我实际上错过了设置mCurrentScreen的一行代码，并且switch语句没有正确传递，因此它没有触发。此外，mRenderer 变量在我的任何 cpp 文件中都没有正确设置，因此每当我尝试使用它时都会返回"无效渲染器"。以下是工作代码，感谢大家的帮助，它引导我朝着正确的方向前进;

#pragma once
#include <SDL.h>
#include "Commons.h"
#include "GameScreenManager.h"
#include "GameScreenLevel1.h"
#include "GameScreen.h"
GameScreenManager::GameScreenManager(SDL_Renderer* renderer, SCREENS startScreen)
{
    mRenderer = renderer;
    GameScreen* mCurrentScreen = NULL;
    ChangeScreen(startScreen);
}
GameScreenManager::~GameScreenManager()
{
    mRenderer = NULL;
    delete mCurrentScreen;
    mCurrentScreen = NULL;
}
void GameScreenManager::Render()
{
    mCurrentScreen->Render();
}
void GameScreenManager::Update(float deltaTime, SDL_Event e)
{
    mCurrentScreen->Update(deltaTime, e);
}
void GameScreenManager::ChangeScreen(SCREENS newScreen)
{
    //Clear up the old screen
    if (mCurrentScreen != NULL)
    {
        delete mCurrentScreen;
    }
    GameScreenLevel1* tempScreen;
    switch (newScreen)
    {
    case SCREEN_INTRO:
        break;
    case SCREEN_MENU:
        break;
    case SCREEN_LEVEL1:
        tempScreen = new GameScreenLevel1(mRenderer);
        mCurrentScreen = (GameScreen*)tempScreen;
        tempScreen = NULL;
        break;
    case SCREEN_LEVEL2:
        break;
    case SCREEN_GAMEOVER:
        break;
    case SCREEN_HIGHSCORES:
        break;
    default:
        break;
    }
}