Comment by kevin_thibedeau

1 day ago

There are (rare) times when you want negative array indices. C lets you index in both directions from a pointer to the middle of an array. That's why array indexing is signed in C. Some libc ctypes lookup tables do this. For sizing there is no strong case for negatives other than to shoehorn them into signed operations.

4 comments

kevin_thibedeau

CodeArtisan 10 hours ago

>That's why array indexing is signed in C

C23 updated the definition of the [] operator to disallow negative subscripts with array type. I think you have to explicitly convert the array to a pointer type now.

    int a[2];
    a[-1]; // not ok
    (&a[0])[-1] // ok

C23: https://cstd.eisie.net/c2y.html#6.5.3.2

C11: https://port70.net/~nsz/c/c11/n1570.html#6.5.2.1

throwaway894345 1 day ago

That’s interesting but seems pretty dangerous. How do you know you aren’t going to decrement off the front of the array? Keeping the pointer to the first element in the array and using offsets seems safer for humans and I don’t think the computer would care.

mmilunic 1 day ago

Kinda a smart alec response, but how do you know you aren’t going to increment off the end of the array when operating normally? I guess it is twice the danger.
8note 1 day ago

i dont want an unsigned int either though. how do you know your arbitrary sized number is inside the size of the array?
best off having a bespoke type that understands how big the array its indexing is