no_std

A Rust program that uses only the core library, because there is no operating system underneath.

A #![no_std] crate links against core (and optionally alloc) instead of std, so it has no files, threads or heap unless the program provides them.

Examples

ESP32-C6 firmware starts with #![no_std] because there's no operating system to provide files, threads or a heap by default.
A no_std crate still has core, so integers, slices and Option work, but std::fs doesn't exist.