GetWindowLongPtr function

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

Note To write code that is compatible with both 32-bit and 64-bit versions of Windows, use GetWindowLongPtr. When compiling for 32-bit Windows, GetWindowLongPtr is defined as a call to the GetWindowLong function.

Syntax

C++


LONG_PTR WINAPI GetWindowLongPtr(
  _In_ HWND hWnd,
  _In_ int  nIndex
);

Parameters

hWnd [in]

Type: HWND

A handle to the window and, indirectly, the class to which the window belongs.

nIndex [in]

Type: int

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 a LONG_PTR. To retrieve any other value, specify one of the following values.

Value	Meaning
GWL_EXSTYLE -20	Retrieves the extended window styles.
GWLP_HINSTANCE -6	Retrieves a handle to the application instance.
GWLP_HWNDPARENT -8	Retrieves a handle to the parent window, if there is one.
GWLP_ID -12	Retrieves the identifier of the window.
GWL_STYLE -16	Retrieves the window styles.
GWLP_USERDATA -21	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.
GWLP_WNDPROC -4	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.

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

Value	Meaning
DWLP_DLGPROC DWLP_MSGRESULT + sizeof(LRESULT)	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 0	Retrieves the return value of a message processed in the dialog box procedure.
DWLP_USER DWLP_DLGPROC + sizeof(DLGPROC)	Retrieves extra information private to the application, such as handles or pointers.

Return value

Type:

Type: LONG_PTR

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

Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll
Unicode and ANSI names	GetWindowLongPtrW (Unicode) and GetWindowLongPtrA (ANSI)