The GetClassLong function retrieves the specified 32-bit (long) value from the WNDCLASSEX structure associated with the specified window.
Syntax
DWORD GetClassLong(
HWND hWnd,
int nIndex
);
Parameters
- hWnd
-
[in] Handle to the window and, indirectly, the class to which the window belongs.
- nIndex
-
[in] Specifies the 32-bit value to retrieve. To retrieve a 32-bit 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 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 retrieve any other value from the WNDCLASSEX structure, specify one of the following values.
GCW_ATOM- Retrieves an
ATOM value that uniquely identifies the window class. This is the same atom that the RegisterClassEx function returns.
GCL_CBCLSEXTRA- Retrieves the size, in bytes, of the extra memory associated with the class.
GCL_CBWNDEXTRA- 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 GetWindowLong.
GCL_HBRBACKGROUND- Retrieves a handle to the background brush associated with the class.
GCL_HCURSOR- Retrieves a handle to the cursor associated with the class.
GCL_HICON- Retrieves a handle to the icon associated with the class.
GCL_HICONSM- Retrieves a handle to the small icon associated with the class.
GCL_HMODULE- Retrieves a handle to the module that registered the class.
GCL_MENUNAME- Retrieves the address of the menu name string. The string identifies the menu resource associated with the class.
GCL_STYLE- Retrieves the window-class style bits.
GCL_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.
Return Value
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 class memory by specifying a nonzero value in the
cbClsExtra member of the WNDCLASSEX structure used with the RegisterClassEx function.
Windows 95/98/Me: GetClassLongW is supported by the Microsoft Layer for Unicode (MSLU). Note that subsequent calls to this function will overwrite the results of previous calls, so you must save any results that you want to use later. To use this version, you must add certain files to your application, as outlined in Microsoft Layer for Unicode on Windows 95/98/Me Systems.
Function Information
| Minimum DLL Version | user32.dll |
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| Header | Declared in Winuser.h, include Windows.h |
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| Import library | User32.lib |
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| Minimum operating systems |
Windows 95, Windows NT 3.1 |
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| Unicode | Implemented as
ANSI and Unicode versions. |
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See Also