Every window class needs a class name to distinguish one class from another. Assign a class name by setting the lpszClassName member of the WNDCLASSEX structure to the address of a null-terminated string that specifies the name. Because window classes are process specific, window class names need to be unique only within the same process. Also, because class names occupy space in the system's private atom table, you should keep class name strings as short a possible.
The GetClassName function retrieves the name of the class to which a given window belongs.