[sim7c00]

I dont know either.

int somearray[10];

new_ptr = somearray + signed_value;

or

element = somearray[signedvalue];

this seems almost criminal to how my brain does logic/C code.

The only thing i could think of is this:

somearray+=11; somearray[-1] // index set to somearray[10] ??

if i'd see my CPU execute that i'd want it to please stop. I'd want my compiler to shout at me like a little child, and be mean until i do better.

-Wall -Wextra -Wextra -Wpedantic <-- that should flag i think any of these weird practices.

As you stated tho, i'd be keen to learn why i am wrong!

[windward]

In the implementation of something like a deque or merge sort, you could have a variable that represents offsets from pointers but which could sensibly be negative. C developers culturally aren't as particular about theoretical correctness of types as developers in some other languages - there's a lot of implicit casting being used - so you'll typically see an `int` used for this. If you do wish to bring some rigidity to your type system, you may argue that this value is distinct from a general integer which could be used for any arithmetic and definitely not just a pointer. So it should be a signed pointer difference.

Arrays aren't the best example, since they are inherently about linear, scalar offsets, but you might see a negative offset from the start of a (decayed) array in the implementation of an allocator with clobber canaries before and after the data.

[sim7c00]

thanks a lot for this. definitely gonna look at these sorts to see whats going on :D interesting!

[mandarax8]

Any kind of relative/offset pointers require negative pointer arithmetic. https://www.gingerbill.org/article/2020/05/17/relative-point...

[poly2it]

I don't think you can make such a broad statement and be correct in all cases. Negative pointer arithmetic is not by itself a reason to use signed types, except if you are:

1. Certain your added value is negative.

2. Checking for underflows after computation, which you shouldn't.

The article was interesting.