Objective C++ lvalue required as unary '&' operand

Question

I'm working on a game engine using SDL2 my method have error 'lvalue required as unary '&' operand'

// 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];
    }
}

I'm coding it in objective-c++ using codeblocks creator on windows and compiler gcc

Answer 1

without knowing environment I can't answer... but I am guessing that you could probably do one of a couple of different things (depending on what the type actually is):

//(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]