GetClassLong

GetClassLong

The GetClassLong function retrieves the specified 32-bit (long) value from the WNDCLASS structure associated with the specified window.

DWORD GetClassLong(

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 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 WNDCLASS structure, specify one of the following values:

Value	Action
GCW_ATOM	Retrieves an ATOM value that uniquely identifies the window class. This is the same atom that the RegisterClass 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 and GetWindowWord .
GCL_HBRBACKGROUND	Retrieves the handle of the background brush associated with the class.
GCL_HCURSOR	Retrieves the handle of the cursor associated with the class.
GCL_HICON	Retrieves the handle of the icon associated with the class.
GCL_HICONSM	Retrieves the handle of the small icon associated with the class.
GCL_HMODULE	Retrieves the handle of 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 associated with the class.

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 class memory by specifying a nonzero value in the cbClsExtra member of the WNDCLASS structure used with the RegisterClass function.