[spanbuf.members]
31 Input/output library [input.output]
31.9 Span-based streams [span.streams]
31.9.3 Class template basic_spanbuf [spanbuf]
31.9.3.4 Member functions [spanbuf.members]
std::span<charT> span() const noexcept;
Returns: If ios_base::out is set in mode, returns std::span<charT>(pbase(), pptr()), otherwise returns buf.
void span(std::span<charT> s) noexcept;
Postconditions:
If ios_base::out is set in mode, pbase() == s.data() && epptr() == pbase() + s.size() is true;
- in addition, if ios_base::ate is set in mode, pptr() == pbase() + s.size() is true,
- otherwise pptr() == pbase() is true.
If ios_base::in is set in mode, eback() == s.data() && gptr() == eback() && egptr() == eback() + s.size() is true.