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 2024. The current version is 1.89.0.

http::basic_file_body::writer::get

boost::optional< std::pair< const_buffers_type, bool > >
get(
    error_code& ec);