The WM_SIZE message is sent to a window after its size has changed.

A window receives this message through its WindowProc function.

Syntax

    WM_SIZE
        WPARAM wParam
        LPARAM lParam

Parameters

• wParam Specifies the type of resizing requested. This parameter can be one of the following values.
  • SIZE_MAXHIDE Message is sent to all pop-up windows when some other window is maximized.
  • SIZE_MAXIMIZED The window has been maximized.
  • SIZE_MAXSHOW Message is sent to all pop-up windows when some other window has been restored to its former size.
  • SIZE_MINIMIZED The window has been minimized.
  • SIZE_RESTORED The window has been resized, but neither the SIZE_MINIMIZED nor SIZE_MAXIMIZED value applies.
• lParam The low-order word of lParam specifies the new width of the client area. The high-order word of lParam specifies the new height of the client area.

Return Value
If an application processes this message, it should return zero.

RemarksIf the programming:windows:SetScrollPos or programming:windows:MoveWindow function is called for a child window as a result of the WM_SIZE message, the bRedraw or bRepaint parameter should be nonzero to cause the window to be repainted.

Although the width and height of a window are 32-bit values, the lParam parameter contains only the low-order 16 bits of each.

Notification Requirements

• Minimum DLL Version None
• Header Declared in Winuser.h, include Windows.h
• Minimum operating systems Windows 95, Windows NT 3.1

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Prototype for Message Handler

void on_size(HWND hwnd, UINT state, int cx, int cy)
{
}

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From: MSDN