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Is there a configure option that will cause MPICH to "typedef long MPI_Count" instead?

No, not without someone writing some new configure logic. The ROMIO code that picks this value starts searching at the largest integer type it expects it might find ("long long") and goes down the list of types in decreasing integer rank until it finds one that works. It doesn't look for the type with the smallest integer rank which still yields 8 bytes or anything like that, which is sort of what you are implying would be preferable behavior.

If you actually had a compiler that would give an _error_ when "long long" was used in C++, then we could skip checking "long long" in that case. So maybe "-Werror=long-long"?

This really is a waste of everyone's time. Just add "-Wno-long-long" and move on to a real problem.

Sure, but it still surprises me that MPI_Count requires a C99 type when at least one member of the MPICH team is quite strict about the need for MPICH to use only C89 features in order to work with the Microsoft C compiler. Jeff -- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute [email protected] / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond