Why does my SDL code crash when I move the mouse over the window?

Question

Whenever I move my mouse below where the image renders in my game, the SDL window crashes and closes down.

I have narrowed the crash down to the bit of code where I check to see if the Escape key was pressed and quit my game; the relevant part of my event loop is:

while (SDL_PollEvent(&e))
{
  if (e.type == SDL_QUIT)
  {
    quit = true;
  }
  if (e.key.keysym.sym == SDLK_ESCAPE)
  {
    quit = true;
  }
}

I found that if I remove the if(e.key.keysym.sym... check, the crashing stops. What is wrong with my code?

Answer 1

The SDL_Event type is a union. Only a single member of the union can be active at any point in time. Your crash is likely because you are accessing the key member when it isn't the active member.

The proper way to do this is to check the event's type field before accessing the rest of it: if (e.type == SDL_KEYDOWN && e.key.keysym.sym...)

In practice you'll probably want a switch statement in there as the number of events you have grows.