Can I Trust Pointer Arithmetic In Re-Allocated Memory?

Bear with me, as I am not a "professional" programmer, but I was
working on part of program that reads parts of four text files into
a buffer which I re-allocate the size as I read each file. I read some
of the items from the bottom up of the buffer, and some from the
top down, moving the bottom items back to the new re-allocated
bottom on every file read.

Then when I've read all four files, I sort the top and bottom items
separately using qsort(), which takes a pointer to a list of items, and
write the two sorted lists to two new files.

Problem is, I worry that if I just supply a pointer to the first item
in the bottom list to qsort(), it might point out to bozo-land during
the sort because I thought that dynamically re-allocated memory
is not necessarily contiguous. So I've done a little two step where
I write the bottom list to another buffer to do the sorting and writing,
and everything works great, but I'm wondering if I'm wasting time
and worrying about nothing...after all, if I can't trust a pointer to an
arbitrary point in the list, how can I trust a pointer to the start of
the list?

Any light you can shed on how pointers are handled in dynamically
allocated memory would be interesting and helpful...thanks.

---
William Ernest Reid



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