Simple SDL_GetTimer() usage - why isn't it working? - c++

Question

I've tried to use SDL_GetTimer() to make action after passing 1000ms using this piece of code:
while(1)
{
int tajmer;
int czas = SDL_GetTicks();
tajmer = SDL_GetTicks() - czas;
if(tajmer > 1000)
{
MoveUp();
czas = SDL_GetTicks();
}
}
But it causes my program to crash. Any ideas why, or how to implement simple timer correctly?

Answer 1

Every time the loop runs, czas is updated to the current time.
Solution: Move it out of the loop.
int czas = SDL_GetTicks();
while(1)
{
int tajmer;
tajmer = SDL_GetTicks() - czas;
if(tajmer > 1000)
{
MoveUp();
czas = SDL_GetTicks();
}
}
However what you are trying to accomplish could possibly be done in a better way using built in timers:
http://wiki.libsdl.org/SDL_AddTimer
Edit:
Example using SDL_AddTimer.
Uint32 my_callbackfunc(Uint32 interval, void *param);
int main() {
... // don't forget to SDL_Init
...
SDL_AddTimer(1000, my_callbackfunc, NULL);
...
}
Uint32 my_callbackfunc(Uint32 interval, void *param)
{
MoveUp();
return(1000); // or however long to wait before my_callbackfunc should run.
}
If you are currently using classes and want to call a class's method called MoveUp() then perhaps:
class example {
...
void start_moving() {
SDL_AddTimer(1000, my_callbackfunc, (void*)this);
}
...
public void MoveUp() {
...
}
}
Uint32 my_callbackfunc(Uint32 interval, void *param) {
((example*)param)->MoveUp();
return (1000);
}

Answer 2

Continuing on Yujin Wus answer you can also do something like this.
int timer = 0;
int ticks = SDL_GetTicks();
while(true)
{
timer += SDL_GetTicks() - ticks;
ticks = SDL_GetTicks();
if(timer >= 1000)
{
timer -= 1000;
MoveUp();
}
}
Or something like this
const int DELAY = 1000;
int timer = SDL_GetTicks() + DELAY;
while(true)
{
if(timer - SDL_GetTicks() <= 0)
{
timer += DELAY;
MoveUp();
}
}