Home/ Questions/Q 8061483
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-05T10:21:15+00:00

I have a problem with WM_SIZE . I want to capture it using PeekMessage

  • 0

I have a problem with WM_SIZE. I want to capture it using PeekMessage (not WndProc). PeekMessage never receives WM_SIZE, so I post extra user message to window to capture it with PeekMessage like this (code from WnProc) :

case WM_SIZE:
  PostMessageW(hwnd, WM_USER + 1, wParam, lParam);
  break;

The problem is I receive WM_USER + 1 using PeekMessage only when window is maximized or restored. No message when window is resized by its thick frame (I receive WM_SIZE in WndProc though).

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    PeekMessage() can only see messages that were posted to the message queue. That excludes WM_SIZE, it is sent, not posted. Or in other words, it is delivered by SendMessage(), it calls the window procedure directly and bypasses the message queue. So yes, your code starts working because you now repost the message with PostMessage, it is put on the message queue so PeekMessage can see it.

    Something different happens when the user resizes the window. That’s reported by another message: WM_SIZING. It is generated, at a pretty high rate, when Windows starts a modal message loop to implement the resizing operation. It gives due notice of this, you’ll get the WM_ENTERSIZEMOVE when the modal loop starts (user clicks a window corner), WM_EXITSIZEMOVE when it is complete (user releases the button). You’ll get a bunch of WM_SIZING messages, sent to your window procedure. Not posted. And one WM_SIZE to give the final size. One way to not see these reflected versions of these messages is when you call PeekMessage() in your own message loop. It won’t be called when the Windows modal resize loop is active.

    Hard to give better advice, it is really unclear why you are doing this. The “doctor, it hurts, don’t do it then” medical answer is highly likely to be relevant. I suspect you might want to reflect the WM_SIZING message as well. The largest issue is that by the time you retrieve these messages from the queue, the window size has already changed and the notification is just plain stale. Which is why the message is sent and not posted.

    • 0