Rust 1.99 lets Rust define C-style variadic functions

Rust 1.99 stabilizes defining C-compatible functions that accept a variable number of arguments, extending interoperability beyond calling existing C functions. It also stabilizes APIs for querying layout through raw pointers. Separately, the standard-library documentation now advises against recovering and freeing memory through Box::leak, recommending explicit ownership-transfer APIs when later deallocation is intended.

Rust Release Team · Oct 1, 2026

Why it matters

Systems developers gain interoperability features and a concrete memory-management pattern to review.

More context

Try the stable toolchain through rustup, then run your existing tests. Review FFI wrappers and code that later frees leaked boxes; Box::into_raw or Box::into_non_null expresses the intended ownership transfer.

Keep in mind

This is a stable release, but variadic argument handling still has unsafe caller obligations. The leak guidance changes documentation, not language semantics. 1min has not tested application compatibility.

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