hwnd (HWND) - input
If this window is of any of the preregistered WC_* classes the class name returned in the PCHBuffer parameter is in the form "#nnnnn", where "nnnnn" is a group of up to five digits that corresponds to the value of the WC_* class name constant.
lLength (LONG) - input
It must be greater than 0.
PCHBuffer (PCH) - output
If the class name is longer than (lLength-1) only the first (lLength-1) characters of class name are copied.
lRetLen (LONG) - returns
This is the length, excluding the null-termination character.