Thread: SDL: Garbage collection (?) screwing me

I've made a function to load a bitmap and give me a pointer to it.

Code:

void loadBMP(char *fname, SDL_Surface *bmp)
{
    SDL_Surface *tmp = SDL_LoadBMP(fname);
    
    char msg[256];
    
    if (tmp == NULL) {
	   sprintf (msg, "Couldn't initialize: %s\n", SDL_GetError ());
       MessageBox (0, msg, "Error", MB_ICONHAND); 
	   return;
    }

    bmp = SDL_DisplayFormat(tmp);
    SDL_FreeSurface(tmp);
}

But it only seems to stay allocated within the function for some reason.

e.g. if I do

Code:

sprintf(msg, "%d", bmp->w);
MessageBox (0, msg, "Error", MB_ICONHAND);

from within the function, it gives me the width of the bitmap, however if I call that outside the function

Code:

SDL_Surface *bitmap;
loadBitmap("block.bmp", bitmap);
sprintf(msg, "%d", bitmap->w);
MessageBox (0, msg, "Error", MB_ICONHAND);

It crashes the program. How can I stop the data from being garbage collected?

To save passing useless uninitialised values to functions which you're just going to overwrite anyway...

Code:

SDL_Surface * loadBMP(char *fname)
{
    SDL_Surface *bmp;
    SDL_Surface *tmp = SDL_LoadBMP(fname);
    
    char msg[256];
    
    if (tmp == NULL) {
	   sprintf (msg, "Couldn't initialize: %s\n", SDL_GetError ());
           MessageBox (0, msg, "Error", MB_ICONHAND); 
	   return NULL;
    }

    bmp = SDL_DisplayFormat(tmp);
    SDL_FreeSurface(tmp);
    return bmp;
}