How to remove WM_QUIT from message queue ?

[Ali Imran]

1. Is there any way we can remove only WM_QUIT message from message queue, if it is existant ?

regards

[NoHero]

You could filter it in your message loop

while ( GetMessage(&msg, hWnd, 0, 0) )
{
if ( msg.message == WM_QUIT )
{
// Do something
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}

[Ali Imran]

Cant we clear up the application message queue, if the next message is WM_QUIT ?

for example we have following next messages to be processed

1.WM_QUIT
2.WM_NCPAINT
3.WM_PAINT


means that the very next message is WM_QUIT, can we remove it from queue and let the application process 2 and 3 ?

Actually my need is to do this outside of message loop.

regards

[philkr]

This is exactly what NoHero showed you to do.

[Ali Imran]

I am sure my wordings are not clear enough, ok let me try explaining again.

1. At certain point clear the queue if very next message is WM_QUIT remove it
2. Stop all for a while, and perform few actions (e.g. display messagebox)
3. Then let the applciation continue with same message queue.

Now, does the above code do same thing? I think it dispatches all the not-WM_QUIT messages before I take further action. I want only WM_QUIT be removed from queue, then I perform the action and then let the queue continue.
I would like this be done in global view, keeping in mind that there must not be any window handle 'hWnd' involved.

Btw : thank you so much for your response.

regards

[philkr]

Sorry, but I still don't understand the problem. Do you know that you can't exit your program if you don't respond to WM_QUIT message.
I reviewed NoHero's code again and you are right it does not work. The reason is that GetMessage() return 0, if WM_QUIT is received and so the while condition is not met.
My solution would be like this:

while(TRUE)
{
GetMessage(&msg, hWnd, 0, 0); // This always removes the first message from the queue
if ( msg.message == WM_QUIT )
{
// So the first message was WM_QUIT has been removed and you want to ignore it.
// Therefore you do not call DispatchMessage() here.
// You then do your few actions here.
// After that the loop continues with 'same message queue' except WM_QUIT removed
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}

EDIT: If you mean, you want to remove WM_QUIT at an arbitrary position in your code not neccessarily the message loop you can use this.

MSG Msg;
PeekMessage(&Msg, hWnd, 0, 0, PM_NOREMOVE);
if(Msg.message == WM_QUIT)
{
PeekMessage(&Msg, hWnd, 0, 0, PM_REMOVE); // removes WM_QUIT
// Do your stuff here
}

Note that GetMessage() always removes the received message. With PeekMessage you can decide that with the flag (PM_REMOVE or PM_NOREMOVE). Note also: GetMessage() blocks if there is no message waiting in the queue, PeekMessage() returns 0 in that case.

[SuperKoko]

You should not use WM_QUIT message for any other purpose than exiting the application.

Instead you should use a user message (WM_USER+0x1 for example), that you can post on the message queue with PostThreadMessage.
So, in the loop you can test if msg.message==(WM_USER+0x1).

[kirants]

The fact that you are getting a WM_QUIT means you intend to quit. Now, why do you want to prevent that.

If there is any action you need to do before closing, why not handle the WM_CLOSE method and swallow it instead ? Or, in case of dialogs, why not trap WM_COMMAND with IDOK/IDCANCEL to perform necessary action ?

[NoHero]

while(TRUE)
{
GetMessage(&msg, hWnd, 0, 0); // This always removes the first message from the queue
if ( msg.message == WM_QUIT )
{
// So the first message was WM_QUIT has been removed and you want to ignore it.
// Therefore you do not call DispatchMessage() here.
// You then do your few actions here.
// After that the loop continues with 'same message queue' except WM_QUIT removed
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}


This code is completly correct. (Regardless that SuperKoko is completly right with his statement). Just to fix this code here:

GetMessage() can return -1 on error and that means that the given message is incorrect. Anyway your code will never return.

Just read MSDN:

Warning: Because the return value can be nonzero, zero, or -1, avoid code like this:

while (GetMessage( lpMsg, hWnd, 0, 0)) ...
The possibility of a -1 return value means that such code can lead to fatal application errors. Instead, use code like this:

BOOL bRet;

while( (bRet = GetMessage( &msg, NULL, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}

[stober]

I am sure my wordings are not clear enough, ok let me try explaining again.

1. At certain point clear the queue if very next message is WM_QUIT remove it
2. Stop all for a while, and perform few actions (e.g. display messagebox)
3. Then let the applciation continue with same message queue.


MessageBox() also puts messages in the queue, so I don't think the above will work. I suppose you could put all the remaining messages in a vector or linked list (to empty the queue), do your processing, then repost all the messages. That might render all those messages useless, depending on what they are.

[Ali Imran]

Actually not the MessageBox, it is soem processing which does not send any message to any window.