The return type is the one you set when you registered the function, the value is the one returned by the function itself.
w32api_invoke_function() tries to find the previously registered function, named funcname, passing the parameters you provided. The return type is the one you set when you registered the function, the value is the one returned by the function itself. Any of the arguments can be of any PHP type or w32api_deftype() defined type, as needed.