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Some bits on malloc(0) in C being allowed to return NULL

(utcc.utoronto.ca)
49 points ingve | 1 comments | 25 Jun 25 06:15 UTC | HN request time: 0.255s | source
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Lvl999Noob ◴[26 Jun 25 18:50 UTC] No.44390177[source]▶
Can someone tell me a usecase where you want multiple allocations of size 0, each one with a unique address, and each one unique from any other allocation (hence necessarily removing that pointer from being allocated to anything else) but can't use malloc(1) instead?

I think it would be much better if malloc(0) just returned 1 or -1 or something constant. If the programmer needs the allocation to have a unique address, they can call malloc(1) instead.

replies(2): >>44390264 #>>44392169 #
xenadu02 ◴[26 Jun 25 22:38 UTC] No.44392169[source]▶
Because zero-size types exist which you might want to take the address of. Possibly as a result of macro substitution or templating mechanism that only appears in certain build configurations.

It means you don't need a bunch of special-case handling if one out of 27 types ends up with zero size in some situation. It just all works the same way. Especially the unique address part because that would be an annoying source of difficult to track bugs.

replies(1): >>44393846 #
1. Lvl999Noob ◴[27 Jun 25 05:06 UTC] No.44393846[source]▶
Yes. I believe zero sized types should be possible and they should all have the same address. Trying to deref the pointer is UB right away because you do not have the byte under that pointer. As it is, the malloc implementation now needs special casing for 0 sized allocations and different implementations special case it differently. C is supposed to be low level so surface this confusion up. Let the programmer decide if they want a unique address and reserve a byte or a non unique one with no overhead.