Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!apple!voder!pyramid!prls!philabs!sbcs!bnlux0!drs
From: drs@bnlux0.bnl.gov (David R. Stampf)
Newsgroups: comp.lang.c
Subject: Re: Question about VMS C
Message-ID: <607@bnlux0.bnl.gov>
Date: 30 Aug 88 12:51:03 GMT
References: <32725@cca.CCA.COM>
Reply-To: drs@bnlux0.UUCP (David R. Stampf)
Organization: Brookhaven National Lab., Upton, N.Y.
Lines: 59

In article <32725@cca.CCA.COM> g-rh@CCA.CCA.COM (Richard Harter) writes:
>
>	The following came up on VMS C.  Either my understanding of
>C is wrong, or the compiler is broken.  The code ran as follows:
>
>char p[256];
>...
>foo () {
>  ...
>  int i,j, *s[128];
>  ...
>  for (i=0;i<128;i++) s[i] = (int *)malloc(128*sizeof(int));
>  for (i=0;i<128;i++) {
>    p[i] = ' ';
>    p[i+128] = ' ';
>    for (j=0;j<128;j++) s[i][j] = 0;
>    }
>  ...
>  }
>
>When this code was executed sundry things were zeroed outside of s and
>the vectors pointed to by the elements of s.  When the double subscripting
>was changed to *(s[i]+j) = 0 the code executed correctly.  The double
>subscripting executes correctly on a host of UNIX machines and on PRIMOS.
>

	The gnomes at DEC seemed to have really screwed the C compiler in
its latest release.  I wouldn't trust *any* code that uses double subscripting
at all.  For example, the following "textbook" code also crashes and burns:

main ()
{
static char *char_tab[] =
      {
      "Monday",
      "Tuesday"
      };

   int i,j;

   for (i = 0; i < 2; i++)
      for (j = 0; j < 4; j++)
         printf("'%c' '%c'\n",char_tab[i][j],*(char_tab[i] + j));
}

	If you compile it with the optimization off, it produces the correct
output.  Using all of the defaults in compiling however produces completely
erroneous values for the char_tab[i][j] output.  Makes you kind of 
uncomfortable with the rest of their compiler.

	This was compiled with the latest version of their compiler -
V2.4 and under VMS 4.7.  It worked with the previous release of the compiler
and is still broken under VMS 5.0.  I've reported this error to DEC, but
I haven't heard a thing from them other than it also failed on their
machines.  

	You may want to report this as well and find a better C compiler.

	< dave stampf