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

This is an older version of Boost and was released in 2013. The current version is 1.89.0.

null_buffers::const_iterator

A random-access iterator type that may be used to read elements.

typedef const mutable_buffer * const_iterator;