Shows how many characters in an input stream

virtual int showmanyc();

The function returns zero for the default behavior. Derived classes may return a negative one or a non-negative value. A positive value estimates the number of characters available in the sequence. If a positive value is returned, then successive calls to underflow() will not return traits::eof() until at least that number of characters have been extracted from the stream. If showmanyc() returns -1, then calls to underflow() or uflow() will fail.

Note that underflow or uflow might fail by throwing an exception prematurely. The intention is that the calls will not return eof() and will return immediately.