MPI_OP_F2C(3)

💖 MPI_OP_F2C(3) 💖

okay bestie, welcome to the Open MPI manual page for all the handle-translation girlies 🧚 This one's from the Open MPI docs, and it's literally the glow-up guide for moving handles between C and Fortran.

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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

…and what do they do? Translates a C handle into a Fortran handle, or vice versa. That's it, that's the whole job. 💅

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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)

not me noticing MPI_Group is here in the syntax but skipped in the NAME list 👀 that's just how the page is, bestie, we reproduce it as-is, no editing the canon 💀

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🌸 DESCRIPTION 🌸

So here's the tea 🍓: handles travel between Fortran and C by way of an explicit C wrapper that converts Fortran handles into C handles. Fortran does not get direct access to C handles. Nope. Not happening. 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. Iconic of it honestly.

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. 🔁

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.

the way that it literally just mirrors your input back at you, valid → valid, null → null, invalid → invalid 😭 main character energy fr fr

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👑 NOTE 👑

okay so hear me out, this is the important part 🔥

This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined.

🚨 bestie. lowkey. do NOT call this outside the MPI_Init / MPI_Finalize window. There's no error return, no warning, no nothing — just undefined behaviour and vibes. it's giving chaos. don't do it. 🙈

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💜 Copyright 💜

2003-2026, The Open MPI Community

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and that's the whole page, no cap 💖 big love to The Open MPI Community for the copyright (2003-2026, iconic run ✨) and this page is dated Sep 10, 2026 — it's from the Open MPI manual, MPI_OP_F2C(3), and yes you ate that, go convert some handles bestie 🫶🎀