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.

ip::address_v4::operator<

Compare addresses for ordering.

friend bool operator<(
    const address_v4 & a1,
    const address_v4 & a2);