Unsafe Rust versus C and C++

Posted Feb 5, 2025 17:29 UTC (Wed) by Trainninny (guest, #175745)
In reply to: Unsafe Rust versus C and C++ by excors
Parent article: Resistance to Rust abstractions for DMA mapping

Not that this is relevant for the argument that he brought as far as I can see, but, how does that relate to this link?

https://stackoverflow.com/questions/25664848/is-it-allowe...

For C:

>if a member of a union object is accessed after a value has been stored in a different member of the object, the behavior is implementation-defined

Unsafe Rust versus C and C++

Posted Feb 5, 2025 18:34 UTC (Wed) by excors (subscriber, #95769) [Link]

Ah, I think I was mixing up C and C++ - it seems it is generally agreed to be undefined behaviour in C++ (though still allowed by GCC), but probably is allowed in C. Though as that Stack Overflow discussion shows, the C standard is somewhat self-contradictory and vague enough (outside of non-normative footnotes) that I'm not sure anyone can be entirely certain of the intended semantics, and especially can't be certain they'll interpret it the same way as all compiler developers.