Strange segfault from SDL_FreeSurface

Question

I have the following simple SDL code:

#include <SDL.h>
#include <stdbool.h>
#include <stdio.h>

// helpers

bool init(SDL_Window **win, SDL_Surface **surf) {
        int const width = 800;
        int const height = 600;
        if (SDL_Init(SDL_INIT_VIDEO) != 0) {
                fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
                return false;
        }
        *win = SDL_CreateWindow("Picture test",
                                SDL_WINDOWPOS_CENTERED,
                                SDL_WINDOWPOS_CENTERED,
                                width, height, 0);
        if (*win == NULL) {
                fprintf(stderr,
                        "Unable to create window: %s\n",
                        SDL_GetError());
                return false;
        }
        *surf = SDL_GetWindowSurface(*win);
        return true;
}

bool load_media(SDL_Surface **surf) {
        *surf = SDL_LoadBMP("./sample.bmp");
        if (*surf == NULL) {
                fprintf(stderr, "Unable to load data: %s\n", SDL_GetError());
                return false;
        }
        return true;
}

void close(SDL_Window **win, SDL_Surface **surf) {
        SDL_FreeSurface(*surf);
        SDL_DestroyWindow(*win);
        SDL_Quit();
}


int main()
{
        SDL_Window *win;
        SDL_Surface *surf;
        SDL_Surface *img;
        if (!init(&win, &surf)) {
                return EXIT_FAILURE;
        }
        if (!load_media(&img)) {
                return EXIT_FAILURE;
        }
        SDL_BlitSurface(img, NULL, surf, NULL);
        SDL_UpdateWindowSurface(win);
        SDL_Delay(2000);
        close(&win, &img);
}

My code always segfaults on close (the origin of the segfault according to GDB is the line SDL_FreeSurface(*surf)). More strangely, if I replace the call to close with its definition, this still segfaults in exactly the same place. Specifically, if I replace close(&win, &img) with:

SDL_FreeSurface(img);
SDL_DestroyWindow(win);
SDL_Quit();

the code still segfaults at exactly the same place, even though that function is not even being called. Only if I remove the entire close function does this work correctly. I am completely confused as to what could be causing this.

Answer 1

Please rename your function

void close(SDL_Window **win, SDL_Surface **surf)

since close is a standard C library function.

Answer 2

I can confirm this. Same scenario. Even with -Wall and -Wextra the compiler did not spit out a redeclaration warning. Same for open().

I need an experts' opinion if this is a gcc bug.

• Solution 1: declare your close() as a static function (e.g. static close()).
• Solution 2: rename your close() function to something else (e.g. my_close_foo()).