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FWIW, even if MPI_VERSION and MPI_SUBVERSION are set correctly, there’s no guarantee that these types are available. Types are only defined based on what compiler you use. For example, if you use a C89 only compiler, these types will not be available.

Wouldn't the C89-compiled MPICH need to support these datatypes to provide interoperability with C99 code in exactly the same manner as it provides Fortran and C++ types for interoperability with code written in those languages? It is ambiguous in what context the word "use" is used here so maybe I am misinterpreting your statement.

Though with MPICH, that is decided at configure time. If you later add -std=c89, the header does not avoid defining the types. Note that some applications need to build different modules with different language standards.

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configure is the only reliable check for these.

That's what we have always done, but it ends up being quite a lot of configure tests and some people complain because configure takes 100x longer on a multi-million dollar file system than it takes on a laptop, so I was double-checking that they were all necessary.

Filesystem performance is a red herring. Don't compile on the gold-plated filesystem. Use /tmp or /scratch, as suggested by https://www.alcf.anl.gov/user-guides/compiling-and-linking-faq. Every Linux login node has /tmp. Jeff -- Jeff Hammond [email protected]