    When classes for input operation are derived from
hi(streambuf)tt(std::streambuf), they should be provided with an input buffer
of at least one character. The one-character input buffer allows for the use
of the member functions tt(istream::putback) or tt(istream::ungetc).  Strictly
speaking it is not necessary to implement a buffer in classes derived from
tt(streambuf). But using buffers in these classes is strongly advised. Their
implementation is very simple and straightforward and the applicability of
such classes is greatly improved. Therefore, all our classes derived from the
class tt(streambuf) define a buffer of em(at least) one character.
