[Python-Dev] Good way of finding out what C functions we have?

[Brett C.]

Martin v. Löwis wrote:

> "Brett C." <bac at OCF.Berkeley.EDU> writes:
> 
> 
>>Does there happen to be a better way to find out what functions we
>>check for beyond grepping configure.in?  The entire reason I bothered
>>to do so much research is I thought we were only supposed to assume
>>ANSI C with POSIX (which, from what I can tell, strdup() is not).  
> 
> 
> Actually, strdup is in POSIX:
> 
> http://www.opengroup.org/onlinepubs/007904975/functions/strdup.html
> 

Shows how much I know; I found that last night but since it didn't say 
POSIX anywhere I thought it was part of another standard.  I guess the 
"Issue 5" mention means that BASE is POSIX?  Or is IEEE 1003.1 basically 
POSIX?

> If we still check for it, it is because it might not have been
> available on some system, at some point in time.
> 

We don't only check for it, but we have a replacement implementation 
(the comment for Python/strdup.c seems to suggest it is needed by the 
parser).

> 
>>Because of this I would like to list in the Python development guide I
>>am writing up all of the places one can check for info; what
>>configure.in checks for or handles and pyport.h come to mind.  It
>>would be nice to have a place that lists all the places one can check
>>for C functionality that are not in the Python/C API directly.  If
>>people have other places in the code that one should check please let
>>me know so I can make sure it makes it into the doc and prevents me
>>from having to come up with another Brett Newbie Question.  =)
> 
> 
> I would look in pyconfig.h.in as the first thing. There is a pitfall,
> though: presence of some HAVE_foo in pyconfig.h does not mean that
> Python gracefully deals with the absence of foo. When converting
> configure to autoconf 2.5x, I checked all macros to determine whether
> they were still in use, but some may have become unused/not processed
> correctly since. That would be a bug, of course.
> 

What does happen if a HAVE_foo is actually required?  Does the build 
fail or will configure halt and say that the build will fail if you proceed?

And if no one objects I will mention that looking in pyconfig.h.in is a 
good place to look to see what C functions that are non-POSIX and 
non-ANSI C we check for and pyport.h has helpful stuff as well.

-Brett