SetClassLong function

Replaces the specified 32-bit (long) value at the specified offset into the extra class memory or the WNDCLASSEX structure for the class to which the specified window belongs.

Note  This function has been superseded by the SetClassLongPtr function. To write code that is compatible with both 32-bit and 64-bit versions of Windows, use SetClassLongPtr.

Syntax


DWORD WINAPI SetClassLong(
  _In_  HWND hWnd,
  _In_  int nIndex,
  _In_  LONG dwNewLong
);

Parameters

hWnd [in]

Type: HWND

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

nIndex [in]

Type: int

The value to be replaced. To set a 32-bit value in the extra class memory, specify the positive, zero-based byte offset of the value to be set. Valid values are in the range zero through the number of bytes of extra class memory, minus four; for example, if you specified 12 or more bytes of extra class memory, a value of 8 would be an index to the third 32-bit integer. To set any other value from the WNDCLASSEX structure, specify one of the following values.

ValueMeaning
GCL_CBCLSEXTRA
-20

Sets the size, in bytes, of the extra memory associated with the class. Setting this value does not change the number of extra bytes already allocated.

GCL_CBWNDEXTRA
-18

Sets the size, in bytes, of the extra window memory associated with each window in the class. Setting this value does not change the number of extra bytes already allocated. For information on how to access this memory, see SetWindowLong.

GCL_HBRBACKGROUND
-10

Replaces a handle to the background brush associated with the class.

GCL_HCURSOR
-12

Replaces a handle to the cursor associated with the class.

GCL_HICON
-14

Replaces a handle to the icon associated with the class.

GCL_HICONSM
-34

Replace a handle to the small icon associated with the class.

GCL_HMODULE
-16

Replaces a handle to the module that registered the class.

GCL_MENUNAME
-8

Replaces the address of the menu name string. The string identifies the menu resource associated with the class.

GCL_STYLE
-26

Replaces the window-class style bits.

GCL_WNDPROC
-24

Replaces the address of the window procedure associated with the class.

 

dwNewLong [in]

Type: LONG

The replacement value.

Return value

Type:

Type: DWORD

If the function succeeds, the return value is the previous value of the specified 32-bit integer. If the value was not previously set, the return value is zero.

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

Remarks

If you use the SetClassLong function and the GCL_WNDPROC index to replace the window procedure, the window procedure must conform to the guidelines specified in the description of the WindowProc callback function.

Calling SetClassLong with the GCL_WNDPROC index creates a subclass of the window class that affects all windows subsequently created with the class. An application can subclass a system class, but should not subclass a window class created by another process.

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

Use the SetClassLong function with care. For example, it is possible to change the background color for a class by using SetClassLong, but this change does not immediately repaint all windows belonging to the class.

Examples

For an example, see Displaying an Icon.

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

SetClassLongW (Unicode) and SetClassLongA (ANSI)

See also

Reference
GetClassLong
RegisterClassEx
SetClassLongPtr
SetWindowLong
WindowProc
WNDCLASSEX
Conceptual
Window Classes

 

 

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