Re: [PATCH 0/2] Modernize header checks

[Eric Blake]

On 05/31/2013 03:26 PM, Peter Rosin wrote:
> On 2013-05-31 19:19, Eric Blake wrote:
>> That said, would it hurt if autoconf just unconditionally defined the
>> macros that were previously conditionally defined by a probe, so that
>> code that was relying on HAVE_STRINGS_H instead of blind inclusion will
>> still compile?
> 
> How would one do to be portable to both "some versions of FreeBSD" and
> MSVC, then? (MSVC 10 also lacks strings.h, btw) One camp needs
> HAVE_STRINGS_H to be defined and one needs to not have it defined.
> Sounds evil to unconditionally define it under those circumstances. Or
> have I misunderstood something?

Portable only to open toolchains, your choice of:

1. Simplest:
#include <strings.h>
void foo() { strcasecmp(a, b); }

2. Verbose:
#include <string.h>
#if HAVE_STRINGS_H
# include <strings.h>
#endif
void foo() { strcasecmp(a, b); }


Portable to MSVC toolchains:

3. Verbose:
#include <string.h>
#if HAVE_STRINGS_H
# include <strings.h>
#endif
void foo() { strcasecmp(a, b); }

The upshot is that if autoconf only cares about open toolchains (such as
gcc on mingw when porting code to Windows), then it can unconditionally
define HAVE_STRINGS_H (it must define this macro for back-compat to
existing code that only includes <strings.h> inside that test).  But if
autoconf still wants to cater to MSVC, then it must have a way to
specify that the existence of strings.h must be probed.  This way does
not have to be default; most packages need a LOT more work before they
could compile under MSVC in the first place, so asking users that care
about such setups to modify configure.ac to set some witness variable in
order to force a probe instead of a blind define seems okay to me.

Personally, I don't care if any of my packages ever compile under MSVC -
that's due in part to Microsoft's lack of regards towards standards and
unwillingness to provide free tools (free license, not free price); in
part due to the fact that gcc on mingw does just as well; and in part
due to the fact that no one who does care has ever submitted a patch to
any of my project mailing lists even trying to get that to work.
Therefore, I would argue that future autoconf needs a way to minimize
useless probing for strings.h, and it would be nicer (in my eyes) if
this mode were the default; although I could also be persuaded that it
is safer to have the no-probe mode only if I add a witness macro to my
configure.ac.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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