Sdl freesurface causing seg faults when blitting

SDL Development
1

I’ve run into my fair share of seg faults while blitting and gotten around them, but this has got me hitting my head against the wall. i’ll I am trying to do is swap one surface with new one. The order I am calling it is changeSurface(); then drawRect(); Any help would greatly be appreciated.

class surfaceID
{
public:
surfaceID(){s=NULL;name="";}
…
SDL_Surface *s;
…
};

std::vector surfaces;

int gfxengine_sdl::changeSurface(int &id,SDL_Surface *newsurf)
{
if(newsurf==NULL)return -1;
if(id==-1)
{
…
}
if(surfaces[id].s!=NULL)
{

  •    SDL_FreeSurface(surface[id].s); 

  •    //SDL_FreeSurface(surface[id].s);  ///This by passes the seg fault, but then I have memory leakage :(
    }
    surfaces[id].s=newsurf;
    return 1;
    }

int gfxengine_sdl::drawRect(int id)
{
if(id==-1)return -1;
if(surfaces[id].s==NULL) return -1;
SDL_BlitSurface(surfaces[id].s,NULL,screen,&surfaces[id].coords); //seg faults here!!!
return 1;
}

2

Kevron Rees wrote:

I’ve run into my fair share of seg faults while blitting and gotten around them, but this has got me hitting my head against the wall. i’ll I am trying to do is swap one surface with new one. The order I am calling it is changeSurface(); then drawRect(); Any help would greatly be appreciated.

class surfaceID
{
public:
surfaceID(){s=NULL;name="";}
…
SDL_Surface *s;
…
};

std::vector surfaces;

int gfxengine_sdl::changeSurface(int &id,SDL_Surface *newsurf)
{
if(newsurf==NULL)return -1;
if(id==-1)
{
…
}
if(surfaces[id].s!=NULL)
{

  •    SDL_FreeSurface(surface[id].s); 

  •    //SDL_FreeSurface(surface[id].s);  ///This by passes the seg fault, but then I have memory leakage :(
    }

Your diffs refer to ‘surface[id].s’ but your vector is named surface’s’.

surfaces[id].s=newsurf;
return 1;

}

int gfxengine_sdl::drawRect(int id)
{
if(id==-1)return -1;
if(surfaces[id].s==NULL) return -1;
SDL_BlitSurface(surfaces[id].s,NULL,screen,&surfaces[id].coords); //seg faults here!!!
return 1;
}
Are you certain ‘&surface[id].coords’ is resolving as you desire?
???>

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3

int
gfxengine_sdl::drawRect(int
id)

{

if(id==-1)return
-1;

if(surfaces[id].s==NULL)
return
-1;

SDL_BlitSurface(surfaces[id].s,NULL,screen,&surfaces[id].coords);

//seg
faults
here!!!

return
1;

}

Are
you
certain
’&surface[id].coords’
is
resolving
as
you
desire?
???

yes, i thought that might be the issue also so I made coords.w and coords.h match the surface->w and h. What gets me is the only change I have to make is to comment out the SDL_FreeSurface() line and bingo! it works.

4 
SDL_BlitSurface(surfaces[id].s,NULL,screen,&surfaces[id].coords);        //seg faults here!!!

Of course a seg fault is caused by illegal access to memory, and this
line includes 4 pointers … one of them is invalid.

NULL can be ruled out, so the trick would be to break out the other
three pointers onto separate lines.

You could try:
SDL_BlitSurface(surfaces[id].s,
NULL,
screen,
&surfaces[id].coords);

and possibly get the segfault to identify the one it doesn’t like. If
your compiler optomizes away the distinction, you could try:

SDL_Rect tempRect;
= &surfaces[id].coords;

SDL_Surface *tempSurface = surfaces[id].s;

tempRect.x = tempRect.y = 0;
temprect.w = surfaces[id].coords.w // If it blows up here, there’s
//something wrong with &surfaces[id].coords
tempRect.h = surfaces[id].coords.h;

if ((tempSurface->w != tempRect.w) ||
(tempSurface->h != tempRect.h))
{
cerr << “Gotcha, bad pointer : surfaces[id].s”;
exit (-1);
}

SDL_BlitSurface(tempSurface,NULL,screen,&tempRect);===========

It’s not intended to be production quality code, just explicit access to
your pointers on separate lines to see which one is segfaulting.

If it still segfaults while blitting, check ‘screen’.

5

CWC wrote:

= &surfaces[id].coords;

Oops, left some editing trash in there, my mail client makes a poor
compiler.

6

Hi,

Are you trying to use this with the main drawing surface returned by
SDL_SetVideoMode()?

If so, that is why you are seg faulting.

Eddy

Kevron Rees wrote:> int

gfxengine_sdl::drawRect(int
id)
{

if(id==-1)return
-1;

if(surfaces[id].s==NULL)
return
-1;

SDL_BlitSurface(surfaces[id].s,NULL,screen,&surfaces[id].coords);

//seg
faults
here!!!

return
1;
}

Are
you
certain
’&surface[id].coords’
is
resolving
as
you
desire?
???

yes, i thought that might be the issue also so I made coords.w and coords.h match the surface->w and h. What gets me is the only change I have to make is to comment out the SDL_FreeSurface() line and bingo! it works.

SDL mailing list
SDL at lists.libsdl.org
http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org