GetWindowLong

The GetWindowLong function retrieves information about the specified window. The function also retrieves the 32-bit (long) value at the specified offset into the extra window memory of a window.

LONG GetWindowLong(
  HWND hWnd,  // handle of window
  int nIndex  // offset of value to retrieve
);
 

Parameters

hWnd

Handle to the window and, indirectly, the class to which the window belongs.

nIndex

Specifies the zero-based offset to the value to be retrieved. Valid values are in the range zero through the number of bytes of extra window memory, minus four; for example, if you specified 12 or more bytes of extra memory, a value of 8 would be an index to the third 32-bit integer. To retrieve any other value, specify one of the following values:

Value	Action
GWL_EXSTYLE	Retrieves the extended window styles.
GWL_STYLE	Retrieves the window styles.
GWL_WNDPROC	Retrieves the address of the window procedure, or a handle representing the address of the window procedure. You must use the CallWindowProc function to call the window procedure.
GWL_HINSTANCE	Retrieves the handle of the application instance.
GWL_HWNDPARENT	Retrieves the handle of the parent window, if any.
GWL_ID	Retrieves the identifier of the window.
GWL_USERDATA	Retrieves the 32-bit value associated with the window. Each window has a corresponding 32-bit value intended for use by the application that created the window.

The following values are also available when the hWnd parameter identifies a dialog box:

Value	Action
DWL_DLGPROC	Retrieves the address of the dialog box procedure, or a handle representing the address of the dialog box procedure. You must use the CallWindowProc function to call the dialog box procedure.
DWL_MSGRESULT	Retrieves the return value of a message processed in the dialog box procedure.
DWL_USER	Retrieves extra information private to the application, such as handles or pointers.

Return Values

If the function succeeds, the return value is the requested 32-bit value.

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

Remarks

Reserve extra window memory by specifying a nonzero value in the cbWndExtra member of the WNDCLASSEX structure used with the RegisterClassEx function.

Windows CE: The nIndex parameter must be a multiple of 4 bytes. Unaligned access is not supported.

Windows CE does not support the GWL_HINSTANCE and GWL_HWNDPARENT values in the nIndex parameter.

Windows CE 1.0 also does not support the DWL_DLGPROC and GWL_USERDATA value in the nIndex parameter.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winuser.h.
  Import Library: Use user32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also

Window Classes Overview, Window Class Functions, CallWindowProc, RegisterClassEx, SetParent, SetWindowLong, WNDCLASS