[英]How to fix “Exception thrown: read access violation. **Surface** was nullptr. occurred” in SDL2 C++
[英](SDL Render Problem) C++ Exception Thrown: read access violation. THIS was nullptr
每当我运行我的程序时,我会在两个单独的代码行上抛出异常,我应该将其中一个注释掉,问题跳转到另一个但是两个都引用相同的变量。
GameScreenManager.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,那么它将出现在第29行:
mCurrentScreen->Update(deltaTime, e);
“抛出未处理的异常:读取访问冲突。 这是nullptr。发生”
显然,当您调用Render()或update()时,mCurrentScreen字段为NULL。 通过检查mCurrentScreen是否为NULL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。
实际上,我实际上错过了设置mCurrentScreen的一行代码,并且switch语句未正确传递,因此它没有触发。 另外,在我的任何cpp文件中都没有正确设置mRenderer变量,因此每当我尝试使用它时都会返回“Invalid Renderer”。 以下是工作代码,感谢所有人帮助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;
}
}
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