Timer ID in timer call back is different from defined timer ID - c++

Question

I implemented two timers with SetTimer function :
UINT TimerId1 = SetTimer(NULL, IDT_TIMER1, 2000, TimerProc);
UINT TimerId2 = SetTimer(NULL, IDT_TIMER2, 2000, TimerProc);
And pump windows messages with GetMessage loop to get timer messages too :
#define IDT_TIMER1 1
#define IDT_TIMER2 2
int main(int argc, char *argv[], char *envp[])
{
MSG Msg;
UINT TimerId1 = SetTimer(NULL, IDT_TIMER1, 2000, TimerProc);
UINT TimerId2 = SetTimer(NULL, IDT_TIMER2, 2000, TimerProc);
while (GetMessage(&Msg, NULL, 0, 0))
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return 0;
}
Due to handle timer messages, i implemented my custom function callback for my timer :
VOID CALLBACK TimerProc(HWND hWnd, UINT nMsg, UINT nIDEvent, DWORD dwTime)
{
if (nMsg == WM_TIMER)
{
switch (nIDEvent)
{
case IDT_TIMER1:
cout << "Timer 1" << endl;
break;
case IDT_TIMER2:
cout << "Timer 2" << endl;
break;
}
}
}
The problem is in my callback, i cannot get the correct timer id because none of the cases are true. My timer id(s) defined as 1 and 2, but timer id(s) in callback are absolutely different, its something like 31270.
Any Suggestion?

Answer 1

Thread timers (when hWnd is null), as opposed to window timers, do not use the ID you give them - instead they assign their own, which is returned to you by the SetTimer function.
This is described in the docs for SetTimer:
If the hWnd parameter is NULL, and the nIDEvent does not match an
existing timer then it is ignored and a new timer ID is generated.
Note that once a thread timer is created, you can use that ID in future calls to SetTimer to modify it.

Answer 2

This is the solution :
At first notice that in the second parameter of SetTimer function according microsoft page (as #Jonathan Potter guidance) :
nIDEvent
Type: UINT_PTR
A nonzero timer identifier. If the hWnd parameter is NULL, and the nIDEvent does not match an existing timer then it is ignored and a new timer ID is generated.
So, my hWnd for timers are both NULL and there's no matching timer id with 1 and 2. consequently timer id returned by SetTimer (which desired id according application decision) and i have to use that to handle in my callback.
// Defined as public to use in callback
UINT TimerId1;
UINT TimerId2;
And my callback defined as the following :
VOID CALLBACK TimerProc(HWND hWnd, UINT nMsg, UINT nIDEvent, DWORD dwTime)
{
if (nMsg == WM_TIMER)
{
if (nIDEvent == TimerId1)
{
cout << "Timer 1" << endl;
}
if (nIDEvent == TimerId2)
{
cout << "Timer 2" << endl;
}
}
}
The output is :
Timer 2
Timer 1
Timer 2
Timer 1
Timer 2
Timer 1
.
.
.