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Re: Cross-platform availability of header files

From: Zack Weinberg
Subject: Re: Cross-platform availability of header files
Date: Thu, 14 Mar 2013 23:18:45 -0400

On Thursday, March 14, 2013, Paul Eggert wrote:

> On 03/14/2013 06:19 PM, Zack Weinberg wrote:
> > 1) What "interesting portability targets" have I left out?  I only
> > went back in time as far as FreeBSD 7, and I didn't even try to get my
> > hands on any of the surviving proprietary Unixes; is this too
> > shortsighted?
> Yes, I think so.  We regularly get bug reports from people running
> HP-UX, AIX, etc.

It's not going to be easy for me to scrape up one of those; it was hard
enough putting a Solaris-descendant VM together. I wonder if people who do
have them would be willing to run "find /usr/include -name \*.h -print" and
send in the output.

I think we should try to come up with a principled cutoff for how old is
too old, though. I started this thinking POSIX.1-2001 (including XSI, but
maybe not any other options) was a reasonable place to draw the line, but
it turns out Android omits a bunch of that (and not the old junk either) so
it's not so simple.

"You can assume a C89 hosted environment" does still seem like a sound
assertion, though.

> 2) Autoconf currently probes for several of the headers in the "safely
> > assumed to exist everywhere" categories, notably in
> > AC_INCLUDES_DEFAULT.  It seems to me that this is unnecessary.  Would
> > patches to remove under-the-hood checks for the ubiquitous headers,
> > and deprecate macros that do explicit checks for them, be accepted?
> If it's safe to include them now, we should stop checking for them.
> > 3) It's a little tangential, but don't you think it's about time
> > AC_CHECK_HEADERS stopped doing all its tests two different ways?
> I would change this, yes.

I'll see if I can find time to put some patches together.

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