[jamesmunns]

Yeah, just adding, in Rust, there's three main levels:

1. no_std (like no libc + no malloc in C)

2. no_std + alloc (like no libc + malloc in C)

3. std (like a full libc + malloc in C)

The difference between 1 + 2 is like three lines. The difference between 2 + 3 is a change to the entire standard library. ATM only ESP32 devices support option 3 (they build a standard library implementation on top of FreeRTOS/ESP-IDF).

[Sharlin]

The `core` library is still available on `no_std` and contains a lot of useful stuff, so it’s not exactly like no libc on C. That would be `no_core` which is pretty hardcore (heh). The big things missing in `no_std` are

* file and other I/O, including filesystem ops

* access to system time

* threads

* collections and some other things that require an allocator (not many things actually do in Rust’s stdlib!)

* floating-point functions (the types themselves and builtin operators work fine)

`alloc` gives you `Vec`, `String`, `Box`, `BTreeMap/Set`, ref-counted pointers, and a few `Vec`-derived collections like `VecDeque`. Very annoyingly not `HashSet/Map` though, due to a literally single-line dependence on a system entropy source which happens to not be easily factorable out because reasons.