Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
The number of bytes of input available at next_in.
std::size_t avail_in;
If there is no more input, this should be set to zero.
The application must update next_in
and avail_in when avail_in has dropped to zero.