Prevent an Object from destroying prematurely

Question

Here's the (relevant) code for my pro::surface class:

/** Wraps up SDL_Surface* **/ class surface { SDL_Surface* _surf; public: /** Constructor. ** @param surf an SDL_Surface pointer. **/ surface(SDL_Surface*); /** Overloaded = operator. **/ void operator = (SDL_Surface*); /** calls SDL_FreeSurface(). **/ void free(); /** destructor. Also free()s the internal SDL_Surface. **/ virtual ~surface(); }

Now the problem is that in my main function, the object destroys itself (and hence calls the destructor which dangerously free()s the SDL Video Surface!) before the real rendering begins.

int main(int argc, char** argv) { ... // declared here pro::surface screen = SDL_SetVideoMode(320,240,16,SDL_HWSURFACE|SDL_DOUBLEBUF); // event-handling done here, but the Video Surface is already freed! while(!done) { ... } // note that "screen" is not used in this loop. // hence, runtime error here. SDL_Quit() tries to free() the Video Surface again. SDL_Quit(); return 0; }

So my question is, is there any way to stop the pro::surface instance from destroying itself before the program ends? Doing memory management manually works though:

/* this works, since I control the destruction of the object */ pro::surface* screen = new pro::surface( SDL_SetVideoMode(..) ); /* it destroys itself only when **I** tell it to! Muhahaha! */ delete screen; /* ^ but this solution uses pointer (ewww! I hate pointers) */

But isn't there a better way, without resorting to pointers? Perhaps some way to tell the stack to not delete my object just yet?

Is pro::surface "yours"? I don't know about SDL, is it possible to hold the SDL_Surface in a shared pointer instead of a raw pointer? Or at least something with shared pointer semantics? — Chad
– Chad, Commented Mar 12, 2012 at 18:58

Puppy · Accepted Answer · 2017-11-02 10:13:50Z

You violated the Rule of Three, bitch.

pro::surface screen = SDL_SetVideoMode(320,240,16,SDL_HWSURFACE|SDL_DOUBLEBUF);

Is equal to

pro::surface screen = pro::surface(SDL_SetVideoMode(320,240,16,SDL_HWSURFACE|SDL_DOUBLEBUF));

Now double free, because you violated the Rule of Three. So give your class a proper copy constructor/assignment operator, or disallow them and explicitly construct it properly.

Edit: This also explains why your pointer version works fine- because you don't invoke a copy.

Cat Plus Plus · Accepted Answer · 2012-03-12 18:55:11Z

Wrap the screen in a special wrapper, that pairs SDL_SetVideoMode with SDL_Quit instead of SDL_FreeSurface.

pro::screen screen(320, 240, 16, SDL_HWSURFACE | SDL_DOUBLEBUF); // ...

And fix your copy ctor, obviously.

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