C++ header files

Guys,

I got the message below as a support request.  I am not a C++ guy, and I have
never actually read the standard, so I'd like to get some feedback from people
who use it regularly.  This user is requesting that I add:

#ifdef __cplusplus
extern "C"
{
#endif
....

#ifdef __cplusplus
}
#endif

To the main C API header files for C++ users.  ATLAS's present approach is:
   http://math-atlas.sourceforge.net/errata.html#CPPheaders

For the user suggestion, I have several questions:
(1) is the '__cplusplus' macro part of the C++ standard, or a gnu-specific
    extension?
(2) Does the standard say what happens if you have nested extern "C"
    declarations?
(3) What are people's feelings on this proposal?

Thanks,
Clint

>From noreply@...  Sun Jun 22 22:59:13 2008
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Subject: [ math-atlas-Support Requests-2000447 ] Comment on FAQ "How about C++ header files for the C ..."
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Support Requests item #2000447, was opened at 2008-06-23 03:59
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=379483&aid=2000447&group_id=23725

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Problems during install
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Comment on FAQ "How about C++ header files for the C ..."

Initial Comment:
Hello,

I installed ATLAS to do some comparisons with
Intel MKL, AMD ACML etc.  The test code is C++ and I am
testing on FreeBSD 7.0.  I ran into the problem of
linking which is covered in the errata entry
"How about C++ header files for the C interfaces?"
I found this after I had worked out the problem
(and yes I did read the docs - just missed this one
as explained below).

A couple of comments:
 1. The error occurs at link time but the errata
    entry does not mention the link symptoms.
    If you are an expert C++ programmer then maybe it
    is obvious but for others I think that a note about
    the symptoms would be useful (esp when searching
    for symptoms on the web).

 2. At the bottom of the entry it says
    "If you are a C++ programmer using ATLAS, and think
     differently, let me know."
    Well I am not a C++ programmer but I cannot see why
    the 'extern (C)' cannot be added to the cblas.h
    header file with appropriate ifdefs e.g.

#ifdef __cplusplus
extern "C"
{
#endif
...
<the rest of cblas.h file>
...
#ifdef  __cplusplus
}
#endif

   This way it is no-op for C programs and will work
   without C++ programmers having to add noise to their
   code.  It is also used in standard system files
   'grep 'extern "C"' /usr/include/*.h'

 3. As for the "Since ATLAS does not provide full OO
    C++ interfaces, I am reluctant to raise the
    expectation that it does by providing C++ specific
    header files."
    If the above ifdefs were added I do not believe
    it will raise expectations.  Since it is an
    explicit 'extern "C"' you know they are C only
    interfaces.
 4. Of course if you do add the 'extern "C"' as
    to the cblas.h file as suggested, existing code
    would have additional enclosing 'extern "C"'.
    I did a quick test and this does not appear to
    cause any problems.

I have not used ATLAS enough to comment fully on its
usefulness but it does appear to be extremely useful
well written software.
(I did read the ATLAS FAQ ;-)

thanks
--
tony maher    tonymaher@...

----------------------------------------------------------------------

You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=379483&aid=2000447&group_id=23725


**************************************************************************
** R. Clint Whaley, PhD ** Assist Prof, UTSA ** www.cs.utsa.edu/~whaley **
**************************************************************************

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