Standard C++ Library Reference ISO/IEC (VERSION3)

istr.setstate(failbit). In any case, the constructor stores the value returned by
istr.good() in status. A later call to operator bool() delivers this stored value.
basic_istream::sync
int sync();
If rdbuf() is a null pointer, the function returns -1. Otherwise, it calls
rdbuf()->pubsync(). If that returns -1, the function calls setstate(badbit) and
returns -1. Otherwise, the function returns zero.
basic_istream::tellg
pos_type tellg();
If fail() is false, the member function returns rdbuf()-> pubseekoff(0, cur, in).
Otherwise, it returns pos_type(-1).
basic_istream::unget
basic_istream& unget();
The unformatted input function puts back the previous element in the stream, if possible, as if by
calling rdbuf()->sungetc(). If rdbuf() is a null pointer, or if the call to sungetc
returns traits_type::eof(), the function calls setstate(badbit). In any case, it
returns *this.
iostream
typedef basic_iostream<char, char_traits<char> > iostream;
The type is a synonym for template class basic_iostream, specialized for elements of type
char with default character traits.
istream
typedef basic_istream<char, char_traits<char> > istream;
The type is a synonym for template class basic_istream, specialized for elements of type
char with default character traits.