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From: mouse@thunder.mcrcim.mcgill.edu (der Mouse)
Newsgroups: comp.lang.c
Subject: is this array access portable?
Message-ID: <1991Jun23.185351.5695@thunder.mcrcim.mcgill.edu>
Date: 23 Jun 91 18:53:51 GMT
Organization: McGill Research Centre for Intelligent Machines
Lines: 27

Suppose `sometype' is a type, and `something' is a valid thing to
assign to an object of that type, and I write

	sometype foo[40][50];
	sometype *fp;
	int i;

	fp = &foo[0][0];
	for (i=2000;i>0;i--) *fp++ = something;

Is this portable?  (The significant question is whether the wraparound
from the end of one row to the beginning of the next is guaranteed to
work correctly.)  I *think* enough promises are made that this will
work, but I'd like to get a few second opinions before writing this
into some code.  The thing that makes me think it has to work is a
sentence in the New Testament A7.4.8 (page 204): ``[...]: the size of
an array of n elements is n times the size of one element.'', which,
applied recursively, appears to imply that the elements of an
N-dimensional array must be packed together as if in a one-dimensional
array of the appropriate size.  (I'm also not *quite* certain that even
if this is true, a pointer can sleaze past the boundary safely....)

					der Mouse

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