From: jeremy siek <jsiek@XXXXXXXXXX>
Date: Thu, 29 Apr 1999 09:28:00 -0500 (EST)
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Cc: HOLZHEU@XXXXXXXXXX,lumesdaine.1@XXXXXX,jsquyres@XXXXXXXXXX,Subject: C++ MPI constants
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Michael Holzheu has brought to our attention a name conflict between
some macros in stdio.h (SEEK_SET, etc.) and the C++ MPI constants.

He proposes two solutions. 
1. Change all the C++ constants to lowercase, which would be more in
 conformance with the style of the C++ standard libraries.

2. Change just the offending constants by adding a "CPP_" prefix.

Andrew Lumsdaine and I suggest that alternative #1 is the better choice.

I have included below the original email that details the problem.


Regards,

Jeremy Siek


HOLZHEU@XXXXXXXXXX writes:
 > The problem was, that SEEK_SET, SEEK_CUR and SEEK_END are macros which are
 > defined
 > also in "stdio.h". This means that a user cannot use MPI::SEEK_XXX when he
 > included stdio.h,
 > because the preprocessor replaces the SEEK_XXX parts:
 > 
 > in stdio.h
 > ==========
 > 
 > #define SEEK_SET 0
 > 
 > 
 > in mpi.h
 > ========
 > 
 > #define MPI_SEEK_SET 0    /* the C MPI constant */
 > 
 > ...
 > 
 > class MPI
 > {
 > 
 >   ....
 > 
 >   enum
 >   {
 >       SEEK_SET = MPI_SEEK_SET,    <<<<< will be replaced if stdio.h has
 > been included before
 >                                         and becomes "0 = 0" ---> Syntax
 > Error
 >   };
 > 
 > in the user program
 > ===================
 > ....
 > fh.Seek(0, MPI::SEEK_SET);  <<<< becomes "fh.Seek(0,MPI::0)" and generates
 > a
 >                                  syntax error when we compile
 > 
 > 
 > The problem is of course more general and perhaps not only the
 > MPI::SEEK_XXX constants are affected.
 > Because we have no MPI_-Prefix in the C++ bindings and all constants are
 > uppercase the probablility
 > of conflicts with preprecessor macros is quite high.
 > 
 > I see the following alternatives to solve this problem:
 > 
 > 1. We define all C++ MPI-constants lowercase (e.g. MPI::seek_set,
 > MPI::seek_cur etc.).
 >    Because by convention preprocessor macros (especially in standard
 > includes) are uppercase
 >    the probablility of conflicts is very low. Other C++ APIs like e.g. C++
 > IO-streams (think of
 >    ios::showpos, ios::left etc.) or Corba do it in this way, too. I think
 > this would be the
 >    best solution. But of course I know this will alter the standard in a
 > very significant way...
 > 
 > 2. We have to find all Constants which conflict with standard include
 > macros and alter their names.
 >    I think the best way to do this is to put a prefix in front of them
 > (e.g. "CPP" or something
 >    like that).
 > 
 >    We know at the moment the three canditates:
 > 
 >    MPI::SEEK_SET --> MPI::CPP_SEEK_SET
 >    MPI::SEEK_CUR --> MPI::CPP_SEEK_CUR
 >    MPI::SEEK_END --> MPI::CPP_SEEK_END
 > 
 >    The problem of this solution if of course that we cannot know which
 > macros will be defined in
 >    the future...
 > 
 > 

------------------------------------------------------------------------
 Jeremy Siek
 Graduate Research Assistant         email: jsiek@XXXXXXXXXX
 Dept. Comp. Sci. & Eng.             phone: (219) 631-3906
 325 Cushing Hall                      fax: (219) 631-9260
 University of Notre Dame              www: http://www.lsc.nd.edu/~jsiek/
 Notre Dame, IN  46556
------------------------------------------------------------------------