On Tue, Jun 26, 2012 at 8:41 AM, Douglas Miller <[email protected]> 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.