DOC: CWnd::OnCommand() Parameters Documented Incorrectly

ID: Q122219

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with: - Microsoft Visual C++, 32-bit Edition, versions 2.0, 5.0

SUMMARY

The online help and the "Class Library Reference" incorrectly describe the CWnd::OnCommand() wParam and lParam as follows:

In Visual C++ 2.0

   wParam  Identifies the command ID of the menu item or control.

   lParam  The low-order word of lParam identifies the control that sends
           the message if the message is from a control. Otherwise the
           low-order word is 0. The high-order word of lParam specifies
           the notification message if the message is from a control. If
           the message is from an accelerator, the high-order word is 1.
           If the message is from a menu, the high-order word is 0.

In Visual C++ 5.0

wParam   The low-order word of wParam identifies the command ID of the menu

item or control. The high-order word of wParam specifies the notification message if the message is from a control. If the message is from an accelerator, the high-order word is 1. If the message is from a menu, the high-order word is 0.

MORE INFORMATION

The description above is valid for Windows-based Applications, but it is invalid for Win32-based Applications. The Win32 API widens the WPARAM type to 32 bits and changes the packing of many of the messages. The parameters for CWnd::OnCommand() should be documented as follows:

   wParam  The low-order word of wParam specifies the identifier of the
           menu item, control, or accelerator. The high-order word
           specifies the notification code if the message is from a
           control. If the message is from an accelerator, the high-order
           word is 1. If the message is from a menu, the high-order word
           is 0.

   lParam  Handle (HWND) of the control sending the message if the message
           is from a control. Otherwise, this parameter is NULL.

REFERENCES

For additional information concerning this issue, please consult the following topics in the Online Help: "WM_COMMAND" and "MFC: Porting Tips".

Keywords          : kbdocerr kbMFC KbUIDesign kbVC kbVC500bug 
Version           : 2.0 5.0
Platform          : NT WINDOWS

Last Reviewed: May 24, 1998