INFO: CWnd::OnCommand() Parameters Documented Incorrectly

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SUMMARY

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

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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.

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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.

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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.

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REFERENCES

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

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APPLIES TO

Microsoft Foundation Class Library 4.2, when used with:

Microsoft Visual C++ 2.0 Professional Edition
Microsoft Visual C++ 5.0 Enterprise Edition
Microsoft Visual C++ 5.0 Professional Edition

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Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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