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From: Vincent Lefevre <vincent-news@vinc17.net>
Newsgroups: comp.std.c
Subject: May a string span multiple, independent objects?
Date: Wed, 3 Jul 2024 14:31:27 -0000 (UTC)
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ISO C17 (and C23 draft) 7.1.1 defines a string as follows: "A string
is a contiguous sequence of characters terminated by and including
the first null character."

But may a string span multiple, independent objects that happens
to be contiguous in memory?

For instance, is the following program valid and what does the ISO C
standard say about that?

#include <stdio.h>
#include <string.h>

typedef char *volatile vp;

int main (void)
{
  char a = '\0', b = '\0';
  vp p = &a, q = &b;

  printf ("%p\n", (void *) p);
  printf ("%p\n", (void *) q);
  if (p + 1 == q)
    {
      a = 'x';
      printf ("%zd\n", strlen (p));
    }
  if (q + 1 == p)
    {
      b = 'x';
      printf ("%zd\n", strlen (q));
    }
  return 0;
}

If such a program is valid, would there be issues by working with
pointers on such a string, say, dereferencing p[1] in the first "if"
(which is normally UB)?

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)