C++ 目标C和x2B+；左值要求为一元'&'；操作数

我正在使用SDL2开发一个游戏引擎。我的方法有错误“一元需要左值”和“操作数”

// Class Enviroment
@interface Environment : NSObject
{
    SDL_Rect groundPos;
}

// Class Game
@interface Game: NSObject
{
    -(SDL_Surface *) addItem: (const char *) file andRegion: (SDL_Rect *) region
    {
         SDL_Surface * temp;
         SDL_Surface * formatted;
         temp = IMG_Load(file);
         formatted = SDL_ConvertSurface(temp, temp->format, NULL);
         temp = NULL;
         return formatted;
    }

    -(void) loadSurfaces
    {
         SDL_Surface *ground;
         ground = [self addItem: "media/ground.bmp" andRegion: &environment.groundPos];
    }
}

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我正在用objective-c++在windows上使用codeblocks creator和编译器gcc对其进行编码

而不知道

环境

我无法回答。。。但是我猜你可能会做一些不同的事情（取决于实际的类型）：

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您是否有包括行号在内的完整错误？什么是

environment.groundPos

？它是如何定义的？只是一个猜测：

environment

和类

environment

的实例，是否有

@property

声明

groundPos

？在这种情况下，

environment.groundPos

实际上并不是它看起来的样子：Objective-C被分解成调用

[environment groundPos]

，它将表达式呈现为

和[environment groundPos]

//(POD just passing in a copy of the value by ptr)
SDL_Rect region = environment.groundPos
ground = [self addItem: "media/ground.bmp" andRegion: &region];

//(Environment is a ptr and has a SDL_RECT ptr member)
ground = [self addItem: "media/ground.bmp" andRegion: environment->groundPos];

//(Member is a POD)
ground = [self addItem: "media/ground.bmp" andRegion: &(environment->groundPos)];

//(maybe what you are trying dereference and dot operator, parens to make explicit)

ground = [self addItem: "media/ground.bmp" andRegion: (*environment).groundPos]