[mpich-discuss] Predefined datatype implementation

Jed Brown jedbrown at mcs.anl.gov
Tue Nov 19 09:53:16 CST 2013

My reading of section 2.5.4 (Named Constants) is that predefined MPI
datatypes need not be implemented as compile-time constants/macros, so
one cannot do

  #if defined(MPI_INT64_T)

or use in a switch/case statement.  Perhaps this makes sense if the
Forum some day decides to standardize the ABI, yet all implementations I
know of use macros for these types.  Is there some other language in the
standard that effectively requires them to be macros already?

Since some vendors have been less than precise about setting MPI_VERSION
and MPI_SUBVERSION, configure tests are the only reliable way to
determine availability of such types.
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