---
title: "-fbounds-safety: Enforcing bounds safety for C — Clang 23.0.0git documentation"
url: https://daily.dev/posts/fbounds-safety-enforcing-bounds-safety-for-c-clang-23-0-0git-documentation-pkfwobzcq
source_url: https://clang.llvm.org/docs/BoundsSafety.html
type: article
source: "Hacker News"
published: 2026-02-19T18:18:02.678Z
updated: 2026-02-19T19:19:46.810Z
tags: ["c"]
reading_time: 35
upvotes: 0
comments: 0
language: en
---

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# -fbounds-safety: Enforcing bounds safety for C — Clang 23.0.0git documentation

**[Hacker News](https://daily.dev/sources/hn)** · 35 min read · 0 upvotes · 0 comments

## Summary

Clang's `-fbounds-safety` is a C language extension designed to prevent out-of-bounds memory accesses by enforcing bounds safety through a combination of compile-time checks and runtime traps. The extension introduces bounds annotations (`__counted_by`, `__sized_by`, `__ended_by`, `__single`, `__bidi_indexable`, `__indexable`, `__null_terminated`, etc.) that programmers attach to pointers to express their valid memory ranges. Local variables implicitly become fat/wide pointers carrying bounds metadata, while ABI-visible pointers (function parameters, struct fields, globals) default to `__single` to preserve ABI compatibility. The model supports incremental adoption, interoperates with unannotated C code via `__unsafe_indexable`, and is portable across toolchains via macro fallbacks. It has already been deployed on millions of lines of production C code in a consumer OS. The document is a design specification; the feature is not yet publicly available.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://clang.llvm.org/docs/BoundsSafety.html>

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---

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