preprocessor/3049: Conditional compilation using "#if A==B" broken on i386 Red Hat 7.0.

[behanna at zbzoom dot net]

>Number:         3049
>Category:       preprocessor
>Synopsis:       Conditional compilation using "#if A==B" broken on i386 Red Hat 7.0.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 04 14:16:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Chris BeHanna <behanna@zbzoom.net>
>Release:        gcc version 2.96 20000731 (Red Hat Linux 7.0)
>Organization:
>Environment:
output of uname -a:
Linux sunflower 2.2.16-22smp #1 SMP Tue Aug 22 16:39:21 EDT 2000 i686 unknown
>Description:
Specifically, code that is conditionally compiled using
#if BYTE_ORDER == BIG_ENDIAN
// stuff
#endif
#if BYTE_ORDER == LITTLE_ENDIAN || BYTE_ORDER == PDP_ENDIAN
// stuff
#endif

results in both sections of code getting processed on Red Hat 7.0 if _XOPEN_SOURCE is defined.  The problem does not occur if _XOPEN_SOURCE is not defined.  The attached program reproduces this problem.
>How-To-Repeat:
Compile the attached program with g++ 2.96 20000731 on Red Hat 7.0 PC with the following command:

g++ -D_XOPEN_SOURCE -o t t.cpp

Execute it.  The output will be

big endian
little endian or PDP endian

(i.e., both sections of code are compiled instead of only the LITTLE_ENDIAN section).

As you might expect, this completely prevents any code that includes <arpa/nameser_compat.h> from being able to compile.
>Fix:
I honestly don't know.  If I have time, I'll dig into the source and see if there's anything obvious, and submit a patch.
>Release-Note:
>Audit-Trail:
>Unformatted: