Boost.Asio / standalone Asio

Overview

Write async C++ networking code that compiles on the user's Boost, not the newest one. Asio's API changed shape three times (classic io_service → io_context → C++20 coroutines) and most Asio code on the internet is from the first era, so pick the style from the toolchain first, then follow that style's reference file.

References: Boost.Asio · standalone Asio

Use this skill whenever async C++ networking code is being written or reviewed — and especially when the target toolchain is old, where coroutine examples simply will not compile. The three worked implementations it references are CI-verified from Boost 1.62 (2016) through 1.90.

Step 1: pick the style (do this before writing code)

Determine the Boost (or Asio) version and the C++ standard actually in use — find_package(Boost) output, dpkg -l libboost-dev, brew info boost, CMAKE_CXX_STANDARD, or ask. Do not assume the newest.