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GetClassLongPtrA function (winuser.h)

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Retrieves the specified value from the WNDCLASSEX structure associated with the specified window.

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

Syntax

ULONG_PTR GetClassLongPtrA(
  [in] HWND hWnd,
  [in] int  nIndex
);

Parameters

[in] hWnd

Type: HWND

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

[in] nIndex

Type: int

The value to be retrieved. To retrieve a value from the extra class memory, specify the positive, zero-based byte offset of the value to be retrieved. Valid values are in the range zero through the number of bytes of extra class memory, minus eight; for example, if you specified 24 or more bytes of extra class memory, a value of 16 would be an index to the third integer. To retrieve any other value from the WNDCLASSEX structure, specify one of the following values.

Value Meaning
GCW_ATOM
-32
 Retrieves an ATOM value that uniquely identifies the window class. This is the same atom that the RegisterClassEx function returns.
GCL_CBCLSEXTRA
-20
 Retrieves the size, in bytes, of the extra memory associated with the class.
GCL_CBWNDEXTRA
-18
 Retrieves the size, in bytes, of the extra window memory associated with each window in the class. For information on how to access this memory, see GetWindowLongPtr.
GCLP_HBRBACKGROUND
-10
 Retrieves a handle to the background brush associated with the class.
GCLP_HCURSOR
-12
 Retrieves a handle to the cursor associated with the class.
GCLP_HICON
-14
 Retrieves a handle to the icon associated with the class.
GCLP_HICONSM
-34
 Retrieves a handle to the small icon associated with the class.
GCLP_HMODULE
-16
 Retrieves a handle to the module that registered the class.
GCLP_MENUNAME
-8
 Retrieves the pointer to the menu name string. The string identifies the menu resource associated with the class.
GCL_STYLE
-26
 Retrieves the window-class style bits.
GCLP_WNDPROC
-24
 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.

Return value

Type: ULONG_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.

Remarks

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

Note

The winuser.h header defines GetClassLongPtr as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement Value
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header winuser.h (include Windows.h)
Library User32.lib
DLL User32.dll
API set ext-ms-win-ntuser-windowclass-l1-1-2 (introduced in Windows 10, version 10.0.10240)

See also

Conceptual

GetWindowLongPtr

Reference

RegisterClassEx

SetClassLongPtr

WNDCLASSEX

Window Classes