CallWndRetProc

The CallWndRetProc hook procedure is an application-defined or library-defined callback function used with the SetWindowsHookEx function. The system calls this function after the SendMessage function is called. The hook procedure can examine the message; it cannot modify it.

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

LRESULT CALLBACK CallWndRetProc(
  int nCode,     // hook code
  WPARAM wParam, // current-process flag
  LPARAM lParam  // message data
);

Parameters

nCode

[in] Specifies whether the hook procedure must process the message. If nCode is HC_ACTION, the hook procedure must 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.

wParam

[in] Specifies whether the message is sent by the current process. If the message is sent by the current process, it is nonzero; otherwise, it is NULL.

lParam

[in] Pointer to a CWPRETSTRUCT structure that contains details about the message.

Return Values

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, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_CALLWNDPROCRET hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure does not call CallNextHookEx, the return value should be zero.

Remarks

An application installs the hook procedure by specifying the WH_CALLWNDPROCRET hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winuser.h; include Windows.h.

See Also

Hooks Overview, Hook Functions, CallNextHookEx, CallWndProc, CWPRETSTRUCT, SendMessage, SetWindowsHookEx