How do I use SDL_PeepEvents properly? - c

Question

When I call the function PeekEvents below the program prints zeros on the standard output and never finishes even though I type on the keyboard when the SDL window has focus. Why doesn't the function catch my keystrokes?
void PeekEvents(void)
{
SDL_Event events[1];
int count;
do {
count = SDL_PeepEvents(events, LEN(events), SDL_PEEKEVENT, SDL_EVENTMASK(SDL_KEYDOWN));
printf("%d\n", count);
} while (count == 0);
}
Here is the complete program:
#include <SDL/SDL.h>
#include <stdio.h>
#define LEN(a) ((int) (sizeof (a) / sizeof (a)[0]))
static void PeekEvents(void)
{
SDL_Event events[1];
int count;
do {
count = SDL_PeepEvents(events, LEN(events), SDL_PEEKEVENT, SDL_EVENTMASK(SDL_KEYDOWN));
printf("%d\n", count);
} while (count == 0);
}
static void Init(int *error)
{
SDL_Surface *display;
*error = SDL_Init(SDL_INIT_VIDEO);
if (! *error) {
display = SDL_SetVideoMode(640, 480, 8, 0);
if (display != NULL) {
*error = 0;
} else {
fprintf(stderr, "SDL_SetVideoMode: %s\n", SDL_GetError());
*error = 1;
}
} else {
fprintf(stderr, "SDL_Init: %s\n", SDL_GetError());
*error = 1;
}
}
int main(void)
{
int error;
Init(&error);
if (! error) {
PeekEvents();
}
return error;
}

Answer 1

Documentation states somewhere that SDL_INIT_EVENTS is implicit when using SDL_INIT_VIDEO.
You need to add a call to SDL_PumpEvents in your loop, otherwise no messages will ever get in the queue.
SDL_PumpEvents gathers all the pending input information from devices and places it on the event queue. Without calls to SDL_PumpEvents no events would ever be placed on the queue. Often the need for calls to SDL_PumpEvents is hidden from the user since SDL_PollEvent and SDL_WaitEvent implicitly call SDL_PumpEvents. However, if you are not polling or waiting for events (e.g. you are filtering them), then you must call SDL_PumpEvents to force an event queue update.