Paragraph 8, Notes, of this section seems to mandate an extremely inefficient way of buffer handling for basic_stringbuf, especially in view of the restriction that basic_ostream member functions are not allowed to use xsputn() (see [ostream]): For each character to be inserted, a new buffer is to be created.

Of course, the resolution below requires some handling of simultaneous input and output since it is no longer possible to update egptr() whenever epptr() is changed. A possible solution is to handle this in underflow().