setstate
is.setstate (ios::eofbit);
is.setstate (ios::failbit);
is.setstate (_count == 0
is.setstate (ios::failbit);
is.setstate (ios::failbit);
void setstate(iostate flag) { _state |= flag; // ANSI
extern char *setstate(char *state);
setstate (ios::badbit);
istr->setstate((ios::iostate)errcode);
stream->setstate((ios::iostate)errcode);