The RegisterWindowMessage function defines a new window message that is guaranteed to be unique throughout the system. The message value can be used when sending or posting messages.

Syntax

UINT RegisterWindowMessage(      
    LPCTSTR lpString
);

Parameters

lpString

[in] Pointer to a null-terminated string that specifies the message to be registered.

Return Value

If the message is successfully registered, the return value is a message identifier in the range 0xC000 through 0xFFFF.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The RegisterWindowMessage function is typically used to register messages for communicating between two cooperating applications.

If two different applications register the same message string, the applications return the same message value. The message remains registered until the session ends.

Only use RegisterWindowMessage when more than one application must process the same message. For sending private messages within a window class, an application can use any integer in the range WM_USER through 0x7FFF. (Messages in this range are private to a window class, not to an application. For example, predefined control classes such as BUTTON, EDIT, LISTBOX, and COMBOBOX may use values in this range.)

Windows 95/98/Me: RegisterWindowMessageW is supported by the Microsoft Layer for Unicode (MSLU). To use this, you must add certain files to your application, as outlined in Microsoft Layer for Unicode on Windows 95/98/Me Systems.

Example

For an example, see Finding Text.

Function Information

Minimum DLL Version	user32.dll
Header	Declared in Winuser.h, include Windows.h
Import library	User32.lib
Minimum operating systems	Windows 95, Windows NT 3.1
Unicode	Implemented as ANSI and Unicode versions.

See Also

Messages and Message Queues Overview, PostMessage, SendMessage