In this blog entry by Andrey Karpov entitled, "About
ptrdiff_t" he shows an example,
for (ptrdiff_t i = 0; i < n; i++) a[i] = 0;
However, I'm not sure if that's right, it seems that should be
for (size_t i = 0; i < n; i++) a[i] = 0;
Is this correct?
I know we should also likely be using something like
memset, but let's avoid that entirely. I'm only asking about the type
In a blog post, I argue that you should always refrain from allocating memory blocks larger than
PTRDIFF_MAX(*), because doing so will make compilers such as Clang and GCC generate nonsensical code even if you do not subtract pointers to that block in a way that causes the result to overflow.
(*) Even if
malloc succeeds when you pass it a value larger than
PTRDIFF_MAX. The crux of the problem is that GCC and Clang only generate code that behaves correctly when linked with such a
malloc, but Glibc provides a
malloc function that does not implement this limitation.
If you follow that constraint (which I encourage you to: that's the message of the blog post), then both types are equally correct.
This said, since only positive offsets need to be represented,
size_t would be the natural choice in your example.