Overview
Group
Quick Info

Windows NT
Yes
Win95
Yes
Win32s
Yes
Import Library
user32.lib
Header File
winuser.h
Unicode
WinNT
Platform Notes
None

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

Identifies 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 WNDCLASS structure used with the RegisterClass function.

See Also

CallWindowProc
, GetWindowWord, RegisterClass, SetParent, SetWindowLong, SetWindowWord, WNDCLASS

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