Earlier quoted context omitted.
> Not by my interpretation of n3096 (April 2023 ISO C draft). What clause(s) support the claim that that example is UB? At least at first glance it looks pretty similar to the sometimes-recommended way to perform safe type-punning in C, and the only way to "directly" invoke UB via memcpy (passing pointers to overlapping objects) isn't relevant here. The only suspicious part to me is the size/number of bytes to copy,…
We have no idea whether the bytes that were copied into that object are a valid representation.
Ah, I didn't think of that.
That being said, is there a representation for doubles that could be considered invalid? I thought all double bit patterns are interpretable as a "valid" double, even if you get NaNs.