[Mpi-forum] C++ types inaccessible after #281

Jed Brown jedbrown at mcs.anl.gov
Tue Jun 26 12:16:04 CDT 2012

On Tue, Jun 26, 2012 at 8:41 AM, Douglas Miller <dougmill at us.ibm.com> wrote:

> I've got to raise a concern here. If we start defining MPI datatypes to be
> C++ types then how will an implementation support that with only a C
> compiler? I thought the point of 281 was to eradicate C++ from the standard
> (and start over later if C++ was to be defined in the standard).

The C++ standard specifies the data representation so I don't see any
reason an implementation couldn't opt to implement the predefined MPI_Ops
without actually using std::complex.

An alternative approach is to note that C99 _Complex has the same data
representation as std::complex, then ask implementations to provide
MPI_C_COMPLEX even on systems without C99 (making it usable from C++). This
isn't really a complicated thing, but we definitely have users of complex
types on Windows and cannot use one-sided operations unless a predefined
complex type is available there.
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