MouseProc function

Article
06/30/2023

Description

An application-defined or library-defined callback function used with the SetWindowsHookExA/SetWindowsHookExW function. The system calls this function whenever an application calls the GetMessage or PeekMessageA/PeekMessageW function and there is a mouse message to be processed.

The HOOKPROC type defines a pointer to this callback function. MouseProc is a placeholder for the application-defined or library-defined function name.

LRESULT CALLBACK MouseProc(
  _In_ int    nCode,
  _In_ WPARAM wParam,
  _In_ LPARAM lParam
);

Parameters

nCode [in]

Type: int

A code that the hook procedure uses to determine how to process the message.

If nCode is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.

This parameter can be one of the following values.

Value	Meaning
HC_ACTION 0	The wParam and lParam parameters contain information about a mouse message.
HC_NOREMOVE 3	The wParam and lParam parameters contain information about a mouse message, and the mouse message has not been removed from the message queue. (An application called the PeekMessage function, specifying the PM_NOREMOVE flag.)

wParam [in]

Type: WPARAM

The identifier of the mouse message.

lParam [in]

Type: LPARAM

A pointer to a MOUSEHOOKSTRUCT structure.

Returns

Type: LRESULT

If nCode is less than zero, the hook procedure must return the value returned by CallNextHookEx.

If nCode is greater than or equal to zero, and the hook procedure did not process the message, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_MOUSE hooks will not receive hook notifications and may behave incorrectly as a result.

If the hook procedure processed the message, it may return a nonzero value to prevent the system from passing the message to the target window procedure.

Remarks

An application installs the hook procedure by specifying the WH_MOUSE hook type and a pointer to the hook procedure in a call to the SetWindowsHookExA/SetWindowsHookExW function.

The hook procedure must not install a WH_JOURNALPLAYBACK callback function.

This hook may be called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop.