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From: shankar@hpclscu.HP.COM (Shankar Unni)
Newsgroups: comp.sys.hp
Subject: Re: _HPUX_SOURCE Defintion and ANSI C
Message-ID: <1340157@hpclscu.HP.COM>
Date: 21 Dec 90 20:43:33 GMT
References: <136@bwilab3.UUCP>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 44

>   I am trying to write ANSI C programs that use calls to UN*X specific 
> functions. When compiling in ANSI mode i.e. -Aa the compiler cannot find
> function prototypes and definitions in some header files. In non ANSI mode
> the definitions are found.
> 
> I was told to resolve this problem by #defining _HPUX_SOURCE. This solves
> the problem of the compiler not finding the prototypes but raises some
> questions about what it does. I was also told, by someone else, that the
> _HPUX_SOURCE tells the compiler that I am compiling kernel code. Is this
> true? Is there a better way to get access to the routines than _HPUX_SOURCE?
> What problems am I opening up by using this? (i.e. am I allowing access to
> kernel routines that I am not supposed to?)

The ANSI C standard mandates the contents of certain header files (the
"magnificent 15", including <stdio.h>, <math.h>, <stdlib.h>, etc). These
files can, in a *strictly conforming* ANSI C implementation, only contain
those identifiers that the ANSI C standard says that it can.

The -Aa flag on HP-UX is supposed to make the C compiler present a fully
conformant ANSI C implementation, which is why it suddenly hides all the
non-ANSI symbols under _HPUX_SOURCE.

The convention adopted by the Unix-ish standards (which *also* have
name-space pollution constraints) is to specify that an ANSI C compiler
which defines a certain magic define (-D...) will get a name space that
conforms to that standard:

  -D_POSIX_SOURCE:	Posix 1003.2
  -D_XOPEN_SOURCE:	X/Open 

In the same vein:

  -D_HPUX_SOURCE:	everything on HP-UX.

_HPUX_SOURCE is a superset of _POSIX_SOURCE, which is a superset of the
ANSI C name space.

(By the way, in "compatibility mode", the -D_HPUX_SOURCE is defined
automatically for you, something we cannot do in -Aa mode, because it will
break ANSI C conformance).
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Shankar Unni                                   E-Mail: 
Hewlett-Packard California Language Lab.     Internet: shankar@hpda.hp.com
Phone : (408) 447-5797                           UUCP: ...!hplabs!hpda!shankar