[Mpi-forum] overloading MPI_Init etc.

[Jeff Hammond]

What was ambiguous to me - looking at 2.6.3-4 - was if using MPI_ was
still a protected namespace in C++.  The standard really only says
explicitly that it is so in C.  It is only with an indirect argument
that mpi.h can define both C and C++ bindings that I can see C++ code
not being able to define MPI_ functions.

Note that MyMPI_ was ~exactly~ how I fixed the user's code :-)

Jeff

On Sun, Mar 4, 2012 at 9:39 PM, Fab Tillier <ftillier at microsoft.com> wrote:
> I don't think defining one's own mpi.h is an issue from a compliance perspective.  However, overloading MPI_Init definitely is - the standard reserves the MPI_ namespace, so if it isn't in the standard, it's not standard compliant.  Now, if they named it MyMPI_Init, it'd be fine.
>
> -Fab
>
> Jeff Hammond wrote on Sun, 4 Mar 2012 at 18:22:40
>
>> I have a user who insists it is MPI-compliant to do the following:
>>
>> user file mpi.h, which is included in the application with #include
>> "mpi.h": ================================== #include <mpi.h>
>>
>> <snip>
>>
>> void MPI_Init(int argc, char* argv[], int& my_rank, int& mpi_size, int&
>> Master) {
>>   MPI::Init(argc, argv);
>>   my_rank = MPI::COMM_WORLD.Get_rank();
>>   mpi_size = MPI::COMM_WORLD.Get_size();
>>   Master = 0;
>>
>>   std::cout << "Hello World! I am " << my_rank << " of " << mpi_size
>> << std::endl;
>> }
>>
>> void MPI_finalize()
>> {MPI::Finalize();}
>>
>> ==================================
>>
>> I believe that it is a terrible practice, if not a violation of the
>> MPI standard to:
>> (1) define one's own mpi.h, since this may confuse the preprocessor
>> (or are there precedence rules in the ANSI C standard?) as to which to
>> include first (especially if CC=mpicc or CXX=mpicxx), and
>> (2) overload MPI_Init, even if one is using C++ and relying upon C++
>> name-mangling to avoid a symbol conflict.
>>
>> The user believes that the inability to overload MPI_Init in C++ means
>> that MPI is not compliant with the C++ standard.
>>
>> Thanks,
>>
>> Jeff
>>
>
>
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-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
http://www.linkedin.com/in/jeffhammond
https://wiki.alcf.anl.gov/old/index.php/User:Jhammond
https://wiki-old.alcf.anl.gov/index.php/User:Jhammond