C++ Debian SDL segmentation fault - c++

Question

I am using SDL to create a quiz game program. The code compiles fine, but when I run the output executable, I get a segmentation fault. I am trying to blit a button onto the screen. Here is my code:
#include <SDL2/SDL.h>
#include <SDL2/SDL_ttf.h>
#include <stdio.h>
#undef main
void ablit(SDL_Surface* source, SDL_Surface* destination, int x, int y){
SDL_Rect offset;
offset.x = x;
offset.y = y;
SDL_BlitSurface(source, NULL, destination, &offset);
}
void acreatebutton(int x, int y, int w, int h, SDL_Color fill, SDL_Surface*
screenSurface, const char* buttontext, int fontsize, SDL_Color textfill){
SDL_Rect* buttonrect;
buttonrect->x = x;
buttonrect->y = y;
buttonrect->w = w;
buttonrect->h = h;
int fillint = SDL_MapRGB(screenSurface -> format, fill.r, fill.g,
fill.b);
SDL_FillRect(screenSurface, buttonrect, fillint);
TTF_Font* font = TTF_OpenFont("/usr/share/fonts/truetype/droid/DroidSansMono.ttf", fontsize);
SDL_Surface* buttontextsurface = TTF_RenderText_Solid(font, buttontext, textfill);
ablit(buttontextsurface, screenSurface, 300, 300);
TTF_CloseFont(font);
}
int main(int argc, char** argv){
SDL_Init(SDL_INIT_EVERYTHING);
TTF_Init();
SDL_Window* screen = SDL_CreateWindow("Quiz Game", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 500, 400,SDL_WINDOW_RESIZABLE);
SDL_Surface* screenSurface = SDL_GetWindowSurface( screen );
SDL_FillRect (screenSurface, NULL, SDL_MapRGB( screenSurface->format, 0, 0, 255 ) );
SDL_Color black = {0, 0, 0};
TTF_Font* afont = TTF_OpenFont("/usr/share/fonts/truetype/droid/DroidSansMono.ttf", 35);
SDL_Surface* aQuiz_Game = TTF_RenderText_Solid(afont, "Quiz Game", black);
ablit(aQuiz_Game, screenSurface, 150, 50);
acreatebutton(175, 350, 200, 50, black, screenSurface, "Take Quiz", 35, black);
SDL_UpdateWindowSurface( screen );
SDL_Event windowEvent;
while (true){
if (SDL_PollEvent(&windowEvent))
{
if (windowEvent.type == SDL_KEYUP &&
windowEvent.key.keysym.sym == SDLK_ESCAPE) break;
}
SDL_GL_SwapWindow(screen);
}
TTF_CloseFont(afont);
SDL_Quit();
TTF_Quit();
return 0;
}
Th ablit function is for blitting, and the abutton function is for creating button images.

Answer 1

You should show, where does you code gets to the segfault, otherwise it's difficult to guess.
First culprit could be the line:
TTF_Font* afont = TTF_OpenFont("/usr/share/fonts/truetype/droid/DroidSansMono.ttf", 35);
You create the font, but doesn't check if it succeeded. If the font file doesn't exist on you computer, you will probably get a segmentation fault.
Second problem is in the function acreatebutton. You declare buttonrect as a pointer, but never initialize it! It's an UB and may do anything, e.g. crashing your program.
In this case you probably don't need it to be a pointer at all, so changing it to a simple variable on the stack should work:
SDL_Rect buttonrect;
buttonrect.x = x;
/* more code ... */
SDL_FillRect(screenSurface, &buttonrect, fillint);
You can find both these problems very easily.
Enable all warnings. GCC will tell you about uninitialized pointer when compiling (I recommend adding -Wall -Wextra -pedantic to you g++ flags).
Learn to use a debugger (GDB is an excelent one). The would tell you everything.
Try a memory sanitizer (compile with -fsanitize=address -g). It will very nicely show you, what went wrong.