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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| Yes
| Import Library
| user-defined
| Header File
| winuser.h
| Unicode
| No
| Platform Notes
| HOOKPROC
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MessageProc
The MessageProc hook procedure is an application-defined callback function the system calls
after an input event occurs in a dialog box, message box, menu, or scroll bar,
but before the message generated by the input event is processed. The hook
procedure can monitor messages for a dialog box, message box, menu, or scroll bar
created by a particular application or all applications.
LRESULT CALLBACK MessageProc(
int code,
| // hook code
| WPARAM wParam,
| // undefined
| LPARAM lParam
| // address of structure with message data
| );
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Parameters
code
Specifies the type of input event that generated the message. This parameter
can be one of the following values:
Value
| Meaning
| MSGF_DDEMGR
| The input event occurred while the Dynamic Data Exchange Management Library
(DDEML) was waiting for a synchronous transaction to finish. For more information
about DDEML, see Dynamic Data Exchange Management Library.
| MSGF_DIALOGBOX
| The input event occurred in a message box or dialog box.
| MSGF_MENU
| The input event occurred in a menu.
| MSGF_NEXTWINDOW
| The input event occurred as a result of the user's pressing the ALT+TAB key combination to activate a different window.
| MSGF_SCROLLBAR
| The input event occurred in a scroll bar.
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If code is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and return the value returned by CallNextHookEx.
wParam
Specifies a NULL value.
lParam
Points to an MSG structure.
Return Values
If the hook procedure processes the message, the return value must be a
nonzero value. Otherwise, it must be zero.
Remarks
An application installs the hook procedure by specifying the WH_MSGFILTER hook type and the address of the hook procedure in a call to the SetWindowsHookEx function.
If an application that uses the DDEML and performs synchronous transactions
must process messages before they are dispatched, it must use the WH_MSGFILTER
hook.
MessageProc is a placeholder for the application-defined function name.
See Also
CallNextHookEx, SetWindowsHookEx, MSG
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