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From: schmidt@glacier.ics.uci.edu (Doug Schmidt)
Newsgroups: comp.lang.c
Subject: function call argument evaluation and global variables
Message-ID: <21448@paris.ics.uci.edu>
Date: 22 Aug 89 21:12:11 GMT
Sender: news@paris.ics.uci.edu
Reply-To: schmidt@glacier.ics.uci.edu (Doug Schmidt)
Organization: University of California, Irvine - Dept of ICS
Lines: 51

Hi,

  I've got a short question.  Does the ANSI C standard place any
restrictions on the evaluation of parameters to functions?  In
particular, is the following program portable in a fully conforming
ANSI C compiler (I know it `fails' on non-ANSI C compilers):

----------------------------------------
int number = 100;

int 
bar ()
{
  return number += 1000;
}

foo (a, b)
int a, b;
{
  printf ("%d, %d, %d\n", a, b, number);
}

main ()
{
  foo (number, bar ());
}
----------------------------------------

This program prints

1100, 1100, 1100

if function bar () is evaluated before global variable `number.'
On the other hand, the program prints

100, 1100, 1100

if the evaluation is reversed.

I realize that to be portable one should not really upon such
behavior; I'm just interested to know whether the standard defines the
behavior here, or whether it is `caveat programmer!'

thanks,

  Doug
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