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.

If you are retrieving a pointer or a handle, this function has been superseded by the [GetWindowLongPtr] function. (Pointers and handles are 32 bits on 32-bit Microsoft Windows and 64 bits on 64-bit Windows.) To write code that is compatible with both 32-bit and 64-bit versions of Windows, use [GetWindowLongPtr].

Syntax

    LONG GetWindowLong(
        HWND hWnd,
        int nIndex
    );

Parameters

• hWnd [in] Handle to the window and, indirectly, the class to which the window belongs.
• nIndex [in] 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.
  • GWL_EXSTYLE Retrieves the extended window styles. For more information, see CreateWindowEx.
  • 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 a handle to the application instance.
  • GWL_HWNDPARENT Retrieves a handle to the parent window, if any.
  • GWL_ID Retrieves the identifier of the window.
  • GWL_USERDATA Retrieves the user data associated with the window. This data is intended for use by the application that created the window. Its value is initially zero. The following values are also available when the hWnd parameter identifies a dialog box.
  • 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 Value
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.

If SetWindowLong has not been called previously, GetWindowLong returns zero for values in the extra window or class memory.

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

Windows 95/98/Me: GetWindowLongW is supported by the Microsoft Layer for Unicode (MSLU). GetWindowLongA is also supported to provide more consistent behavior across all Windows operating systems. To use these versions, you must add certain files to your application, as outlined in Microsoft Layer for Unicode on Windows 95/98/Me Systems .

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.

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See also programming:windows:window value offsets