CharT operator*() const;
pointer operator->() const;
|(2)|| (since C++11)
Reads a single character by calling sbuf_->sgetc() where sbuf_ is the stored pointer to the stream buffer.
The behavior is undefined if the iterator is end-of-stream iterator.
 Return value
1) The value of the obtained character.
2) An object of unspecified type, such that given an istreambuf iterator
i, the expressions (*i).m and i->m have the same effect.
May throw implementation-defined exceptions.