Why setTimer is not working? [duplicate] - c

Question

This question already has answers here:
Can I use a SetTimer() API in a console C++ application?
(6 answers)
Closed 9 years ago.
I have below program. I would like to know how setTimer works. So, I wrote a program but could not able to understand why TimerProc function not getting called. Why? What else need to be done to fire setTimer/TimerProc. Please help.
#include <windows.h>
#include <stdio.h>
VOID CALLBACK TimerProc(
HWND hwnd, // handle of window for timer messages
UINT uMsg, // WM_TIMER message
UINT idEvent, // timer identifier
DWORD dwTime // current system time
) {
printf("from callback\n");
}
int main(int argc, char *argv[])
{
UINT timerid = SetTimer(NULL,1,1000,TimerProc);/*changed the time from 1 to 1000, but no effect*/
printf("timerid %d\n",timerid);
int i,j;
//delay loop, waiting for the callback function to be called
for(j=0;j<0xffffffff;j++);
/*{
printf("%d\n", j);
}*/
printf("done \n");
system("PAUSE");
return 0;
}

Answer 1

The timer works via a Windows message queue and you have a console application.
If you create a basic Win32 application so you get a window and a message loop, when the WM_TIMER message is caught by the DefWndProc() call, that's where it will do the callback. Of course you can also trap the WM_TIMER yourself.

Answer 2

The SetTimer documentation says:
*When you specify a TimerProc callback function, the default window procedure calls the callback function when it processes WM_TIMER. Therefore, you need to dispatch messages in the calling thread, even when you use TimerProc instead of processing WM_TIMER.*
Instead the delay loop you need something like:
bool bStillBusy = false;
int main()
{
MSG msg;
bStillBusy = true;
id = SetTimer(NULL, 0, 3000, (TIMERPROC) TimerProc);
while(bStillBusy)
{
GetMessage(&msg, NULL, 0, 0);
DispatchMessage(&msg);
}
...
etc.
}
You set the bStillBusy to 'false' in the callback then.

Answer 3

You need to learn the message loop paradigm. You are trying to use Win32 api without actually doing the right Win32 initialization and operations.
If you come from Posix, you'd could use a SIGALRM and alarm.
On windows, I'm afraid you'll have more work to do (like starting a message loop, because even when you provide a callback function, you need a message loop pumping that's calling the default message loop processing function will call your timer's callback, check this:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms644906(v=vs.85).aspx
An application can process WM_TIMER messages by including a WM_TIMER case statement in the
window procedure or by specifying a TimerProc callback function when creating the timer.
When you specify a TimerProc callback function, the default window procedure calls the
callback function when it processes WM_TIMER. Therefore, you need to dispatch messages in
the calling thread, even when you use TimerProc instead of processing WM_TIMER.

Answer 4

Timer are handled using the normal Windows event system, so you need a normal event loop.