MPI_GROUP_F2C(3)

🦋 MPI_GROUP_F2C 🦋

okay bestie, so this one is from the Open MPI manual, section 3, and it's literally the whole "translate my handle" friend group 💅 — MPI_Comm_f2c, MPI_Comm_c2f, MPI_File_f2c, MPI_File_c2f, MPI_Info_f2c, MPI_Info_c2f, MPI_Message_f2c, MPI_Message_c2f, MPI_Op_f2c, MPI_Op_c2f, MPI_Request_f2c, MPI_Request_c2f, MPI_Type_f2c, MPI_Type_c2f, MPI_Win_f2c, MPI_Win_c2f — and their whole job is translating a C handle into a Fortran handle, or vice versa. no cap ✨

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✨ NAME ✨

MPI_Comm_f2c, MPI_Comm_c2f, MPI_File_f2c, MPI_File_c2f, MPI_Info_f2c, MPI_Info_c2f, MPI_Message_f2c, MPI_Message_c2f, MPI_Op_f2c, MPI_Op_c2f, MPI_Request_f2c, MPI_Request_c2f, MPI_Type_f2c, MPI_Type_c2f, MPI_Win_f2c, MPI_Win_c2f — Translates a C handle into a Fortran handle, or vice versa. 🫶

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🌈 SYNTAX 🌈

🎀 C Syntax 🎀

#include <mpi.h>

MPI_Comm MPI_Comm_f2c(MPI_Fint comm)
MPI_Fint MPI_Comm_c2f(MPI_Comm comm)

MPI_File MPI_File_f2c(MPI_Fint file)
MPI_Fint MPI_File_c2f(MPI_File file)

MPI_Group MPI_Group_f2c(MPI Fint group)
MPI_Fint MPI_Group_c2f(MPI Group group)

MPI_Info MPI_Info_f2c(MPI_Fint info)
MPI_Fint MPI_Info_c2f(MPI_Info info)

MPI_Message MPI_Message_f2c(MPI_Fint message)
MPI_Fint MPI_Message_c2f(MPI_Message message)

MPI_Op MPI_Op_f2c(MPI_Fint op)
MPI_Fint MPI_Op_c2f(MPI_Op op)

MPI_Request MPI_Request_f2c(MPI_Fint request)
MPI_Fint MPI_Request_c2f(MPI_Request request)

MPI_Datatype MPI_Type_f2c(MPI_Fint datatype)
MPI_Fint MPI_Type_c2f(MPI_Datatype datatype)

MPI_Win MPI_Win_f2c(MPI_Fint win)
MPI_Fint MPI_Win_c2f(MPI_Win win)

(yes, the group lines are written exactly like that in the page — MPI Fint and MPI Group, no underscore. that's the source, bestie, I don't make the rules 💀)

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💖 DESCRIPTION 💖

so here's the vibe check 🧚 handles get passed between Fortran and C using an explicit C wrapper to convert Fortran handles to C handles. There is no direct access to C handles in Fortran — sorry, that's just not a thing, periodt.

The type definition MPI_Fint is provided in C for an integer of the size that matches a Fortran INTEGER; usually, MPI_Fint will be equivalent to int. 🍓

The handle translation functions are provided in C to convert from a Fortran handle (which is an integer) to a C handle, and vice versa. it's giving translator era, and honestly? iconic 👑

For example, if comm is a valid Fortran handle to a communicator, then MPI_Comm_f2c returns a valid C handle to that same communicator; if comm = MPI_COMM_NULL (Fortran value), then MPI_Comm_f2c returns a null C handle; if comm is an invalid Fortran handle, then MPI_Comm_f2c returns an invalid C handle. main character conversion behaviour tbh ✨

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🩷 NOTE 🩷

⚠️ okay listen up — this function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. that's not a vibe, that's literally undefined behaviour, so please don't 😭💀

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🌸 COPYRIGHT 🌸

2003-2026, The Open MPI Community

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and that's the whole page, bestie — written by the Open MPI girlies, dated Sep 11, 2026, version vibes courtesy of Open MPI. go translate those handles, slay, and remember: MPI_Fint is your friend 💜🦋✨