In some earlier articles, we used the term freestanding. We said that a freestanding implementation is one that operates without the support of a hosted operating system. Think embedded systems, OS kernels, or bare-metal environments where heap allocation, system calls, and exception support are typically unavailable. The C++ standard defines a minimal subset of the language and library that must work in such constrained environments. But I wanted to go slightly deeper, because the term doesn’t come up much in everyday C++ — at least not until you start reading the standard more carefully or until you need to use such an implementation.

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C++ distinguishes between hosted and freestanding implementations. Freestanding targets environments without an OS — embedded systems, kernels, bare-metal — where heap allocation, exceptions, and system calls may be unavailable. The standard guarantees a minimal subset of headers like <cstdint>, <cstddef>, <type_traits>, and parts of <new>, while excluding OS-dependent components like <thread>, <filesystem>, and <iostream>. From C++20 through C++26, the freestanding subset has been steadily expanded to include algorithms, std::span, std::expected, std::mdspan, and smart pointer adapters, enabling more expressive code in constrained environments.

Freestanding standard library

What is actually guaranteed in freestanding

The evolution of freestanding in modern C++