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 2018. The current version is 1.90.0.

zlib::z_params::total_out

The total number of bytes output so far.

std::size_t total_out = 0;