# Comparing dangling pointers

**URL:** <https://internals.rust-lang.org/t/comparing-dangling-pointers/3019>\
**Category:** language design\
**Created:** [December 21, 2015, 5:30pm UTC](https://internals.rust-lang.org/t/comparing-dangling-pointers/3019 "2015-12-21T17:30:40Z")\
**Posts on this page:** 1\
**Showing post:** 31

<div class="post-metadata">

**Author:** ![ranma42](https://avatars.discourse-cdn.com/v4/letter/r/48db29/32.png) [@ranma42](https://internals.rust-lang.org/u/ranma42)\
**Post date:** [January 6, 2016, 10:38pm UTC](https://internals.rust-lang.org/t/comparing-dangling-pointers/3019/31 "2016-01-06T22:38:39Z")

</div>

The [LLVM Reference manual](http://llvm.org/docs/LangRef.html#undefined-values) disagrees:

> This example points out that two ‘undef‘ operands are not necessarily the same. This can be surprising to people (and also matches C semantics) where they assume that “X^X” is always zero, even if X is undefined.

`x` could have a different value every time (if the "undef" is intended in the LLVM way).

---

_[View the full topic](https://internals.rust-lang.org/t/comparing-dangling-pointers/3019)._