The Overloaded void * Operator

Another overloaded ios member function—operator void *—converts the stream to a pointer, so it can be tested as 0 (i.e., the null pointer) or nonzero (i.e., any other pointer value). When a pointer value is used as a condition, C++ interprets a null pointer in a condition as the bool value false and interprets a non-null pointer as the bool value true. If the failbit or badbit has been set for the stream, 0 (false) is returned. The condition in the while statement of lines 29–33 invokes the operator void * member function on cin implicitly. The condition remains true as long as neither the failbit nor the badbit has been set for cin. Entering the end-of-file indicator sets the failbit for cin. The operator void * function can be used to test an input object for end-of-file, but you can also call member function eof on the input object.