On 22 Jul 2009, at 18:02, Christopher Jefferson wrote:
On 22 Jul 2009, at 16:23, Stewart, Robert wrote:
Ultimately are random access iterators *supposed* to be homeomorphic to the integers in the same (apparent) way C indices are?
I'm sure that:
int a[3] int* b = a + 4;
Is illegal C code, as you have gone outside the bounds of your array, even if you never dereference the pointer.
Following your minimalistic example, I'm thinking about: typdef int index; int a[3]; index i = 0; // Index idx is homeomorphic to the integers 'cause it is one. i -= 1000; i += 2002; int b=a[i]; That's clearly ok as idx is 2 and the last line is b=*(a + 2). Whereas. int *p = a; p = p - 1000; // Undefined? p = p + 1002; // Also undefined? int b=*p; Is presumably undefined. That implies to me that pointer arithmetic is *not* like integer arithmetic since the first example is not identical to the second. Baring in mind the old adage of Mark Twain, http://www.quotationspage.com/quote/369.html it seems to me absurd that they are not the same. I guess that's just the way it is. -ed ------------------------------------------------ "No more boom and bust." -- Dr. J. G. Brown, 1997