Raw C String conversion and conversion trait

If you want constant C strings, use c"Hello, World" as recently stabilized instead

Raw CStr

Utilities for working with raw C strings from Rust. This primarily is intended to provide a constant-like C-string at runtime by using a thread local cache. Its usage is extremely niche, and is intended to be used by tsffs and other crates which compile to cdylibs which are loaded by non-rust programs.