undefined | Better HN

0 pointsrseacord6y ago0 comments

Maybe someone else can respond to this as well, but I feel like the primary reason signed overflow is still undefined behavior is because so many optimizations depend upon the undefined nature of signed integer overflow. My advice has always been to use unsigned integer types when possible.

Personally, I would like to get rid of many of the trap representations (e.g., for integers) because there is no existing hardware in many cases that supports them and it gives implementers the idea that uninitialized reads are undefined behavior.

On the other hand, I just wrote a proposal to WG14 to make zero-byte reallocations undefined behavior that was unanimously accepted for C2x.

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saagarjha6y ago

> My advice has always been to use unsigned integer types when possible.

Unsigned types have their own issues, though: they overflow at "small" values like -1, which means that doing things like correctly looping "backwards" over an array with an unsigned index is non-trivial.

> On the other hand, I just wrote a proposal to WG14 to make zero-byte reallocations undefined behavior that was unanimously accepted for C2x.

You're saying that realloc(foo, 0) will no longer free the pointer?

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