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WM_MDICREATE Overview  Group

An application sends the WM_MDICREATE message to a multiple document interface (MDI) client window to create an MDI child window.


wParam = 0;                                     // not used; must be zero 

lParam = (LPARAM) (LPMDICREATESTRUCT) lpmdic;   // creation data 



Points to an MDICREATESTRUCT structure containing information that Windows uses to create the MDI child window.

Return Values

If the message succeeds, the return value is the handle of the new child window.

If the message fails, the return value is NULL.


The MDI child window is created with the style bits WS_CHILD, WS_CLIPSIBLINGS, WS_CLIPCHILDREN, WS_SYSMENU, WS_CAPTION, WS_THICKFRAME, WS_MINIMIZEBOX, and WS_MAXIMIZEBOX, plus additional style bits specified in the MDICREATESTRUCT structure to which the lpmdic parameter points. Windows adds the title of the new child window to the Window menu of the frame window. An application should use this message to create all child windows of the client window.

If an MDI client window receives any message that changes the activation of its child windows while the active child window is maximized, Windows restores the active child window and maximizes the newly activated child window.

When an MDI child window is created, Windows sends the WM_CREATE message to the window. The lParam parameter of the WM_CREATE message contains a pointer to a CREATESTRUCT structure. The lpCreateParams member of this structure contains a pointer to the MDICREATESTRUCT structure passed with the WM_MDICREATE message that created the MDI child window.

An application should not send a second WM_MDICREATE message while a WM_MDICREATE message is still being processed. For example, it should not send a WM_MDICREATE message while an MDI child window is processing its WM_MDICREATE message.

See Also


See also:

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