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 GetWindowLongPtr

The GetWindowLongPtr function retrieves information about the specified window. The function also retrieves the value at a specified offset into the extra window memory.

If you are retrieving a pointer or a handle, this function supersedes the [GetWindowLong] function. (Pointers and handles are 32 bits on 32-bit 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.

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

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 the size of an integer. To retrieve any other value, specify one of the following values. Value Action
  GWL_EXSTYLE Retrieves the extended window styles. For more information, see CreateWindowEx. GWL_STYLE Retrieves the window styles. GWLP_WNDPROC Retrieves the pointer to the window procedure, or a handle representing the pointer to the window procedure. You must use the CallWindowProc function to call the window procedure. GWLP_HINSTANCE Retrieves a handle to the application instance. GWLP_HWNDPARENT Retrieves a handle to the parent window, if there is one. GWLP_ID Retrieves the identifier of the window. GWLP_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. Value Action
  DWLP_DLGPROC Retrieves the pointer to the dialog box procedure, or a handle representing the pointer to the dialog box procedure. You must use the CallWindowProc function to call the dialog box procedure. DWLP_MSGRESULT Retrieves the return value of a message processed in the dialog box procedure. DWLP_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 value.

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

If SetWindowLong or SetWindowLongPtr has not been called previously, GetWindowLongPtr 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.

Requirements

• Windows NT/2000 or later: Requires Windows NT 3.1 or later.
• Windows 95/98/Me: Requires Windows 95 or later.
• Header: Declared in Winuser.h; include Windows.h.
• Library: Use User32.lib.
• Unicode: Implemented as Unicode and ANSI versions on Windows NT/2000.

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