Registered Messages vs. WM_USER

#define SPECIAL_CTRL_CHANGE(WM_USER + 1000)

Therefore the conclusion is to use WM_USER messages only when sending notification messages and not normal windows messages.

One alternative to using custom Windows messages that are based on the WM_USER message is to register your own Windows messages. The idea behind registered messages is to create a unique Windows message based upon a string. Any window that knows the string can obtain the message code and therefore, respond to the predefined message. This allows several components to create custom messages, and by simply concatenating the component name to the message name, they can be sure that their string is unique, and therefore the message code is unique.

Here's an example of how to add the message handler of a registered message on the client side using the MFC message map.

static const UINT MsgSpecialCtrlChange = ::RegisterWindowMessage(SPECIAL_CTRL_CHANGE);
BEGIN_MESSAGE_MAP(...
//{{AFX_MSG_MAP(...
.
.
//}}AFX_MSG_MAP
ON_REGISTERED_MESSAGE(MsgSpecialCtrlChange,
OnSpecialCtrlChange)
END_MESSAGE_MAP()

#define SPECIAL_CTRL_CHANGE _T("Special_Change")

The Windows Common Controls use this type of message routing from the DLL to the user application for several messages such as FindOrReplace command in RichEdit control. The intellimouse messages are also sent with registered messages, instead of creating new windows messages for them.

Date Last Updated: March 5, 1999