Indicate version of C standard that MPI is based on

[bkmgit]

Problem

MPI extends C and Fortran. Both of these have standards bodies which give language specifications that are revised. Revisions in these standards can have implications on functionality that can be included in MPI

Proposal

The main standard should draw from specific versions of C and Fortran standards. Support for additional versions may be indicated in side/complementary documents, but this can be done as a separate issue.

Changes to the Text

Update Chapter 1 to indicate a version of the C standard for the main MPI standard.

Impact on Implementations

Better expectations for functions that compilers need to have to support MPI.

Impact on Users

Better expectation for compilers they can use.

References and Pull Requests

None at present.

[jeffhammond]

Good proposal. Let me know if I can help.

[jeffhammond]

We discussed today. This is relevant to ABI work.

[bkmgit]

Thanks. My understanding is to recommend C 11 ISO/IEC 9899:2011 but indicate that a conservative set of the standard is used, and it should be possible to use other versions such as C99, C17 or C23 with minor header additions.

[jeffhammond]

Not sure if you saw what I wrote on the PR:

The normative language reference for Fortran is ISO/IEC 1539-1:2018.
The language features required to support MPI Fortran bindings
are described in \sectionref{subsec:binding}.

When referring to ISO C, the normative language reference is
ISO/IEC 9899:2018.  MPI does not depend on recent additions
to the ISO C standard and is expected to be compatible with
implementations of ANSI X3.159-1989 and ISO/IEC 9899:1990,
but these documents and no longer published.
More recent releases may have important clarifications
relevant to contemporary compilers.

While MPI does not support C++ bindings, the C bindings are
expected to compile with C++ compilers, because MPI bindings
depend on a subset of language features supported by both.
When necessary, the normative language reference for C++
is ISO/IEC 14882:2020.

It explicitly say that we expect compatibility with C89.

[bkmgit]

Sorry for the delay and thanks for your fast response to this. Made some minor suggestions. It would be good to have some policy. As many MPI codes are long lived and it takes some time for compilers to fully adopt standard features, most features should primarily target specifications from at earliest 5 years before. Newer features may be included, but may be good to explicitly state these.