From: Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: make depend
Date: 24 Jan 2000 13:08:25 -0800
Organization: InterWorld Communications
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Eli Zaretskii <eliz AT is DOT elta DOT co DOT il> writes:

> On Mon, 17 Jan 2000, Andris Pavenis wrote:
> 
> > Including $DJDIR/lib/../include/sys/version.h is a hack how to get
> > definitions of current DJGPP version automatically in. I still think
> > that best would be to force to include stdio.h when one needs version
> > definitions, but there were objections against such solution.
> 
> The main objection is this: the ANSI Standard says that a program
> which doesn't include any header files should still have the same
> behavior as when it does.

How can this be?

Consider:

#include <math.h>

double my_sqrt(double d);
{
  double x;
  return sqrt(d);
}

If you don't include <math.h>, the implicit declaration of `sqrt' will
be used: `int sqrt();'.  So the compiler will use the calling
conventions for an int-returning function instead of a double, and on
most platforms it'll be wrong.  On x86, for instance, you'll get
whatever garbage was in %eax, casted to double.  This is definitely
different behavior than when you do include <math.h>, when you get the
right answer.

Does ANSI really expect every platform to work some magic to make this
work anyhow?  Are there any that actually do?

-- 

Nate Eldredge
neldredge AT hmc DOT edu