On Tue, Oct 26, 2021 at 11:17 PM Derrick Stolee <stolee@xxxxxxxxx> wrote:
(regarding a pointer that "backs up one before the beginning
of the array" as it were)
> I also see the specification saying this is undefined, but I do not
> understand how any reasonable compiler/runtime could do anything
> other than store "path - 1" as if it was an unsigned integer. ...
This Standard C rule dates back to old segmented systems.
If you put some array A into its own segment, and use only
the offset as the "pointer", and the segment offset starts at
zero, then A[0] is at "address zero". So the imaginary element
at A[-1] is at "address max", and a loop like:
for (p = &A[N]; p >= &A[0]; p--)
is an infinite loop.
In practice nobody is using these architectures today, but the
restriction still exists.
Chris
