MPI_FILE_C2F(3)

✨ MPI_FILE_C2F — bestie edition ✨

okay so this page is from the Open MPI crew, and it's actually a whole lil squad of functions, not just one. They all do the same thing in different flavours: swap a C handle for a Fortran handle, or the other way around. 🔄

• 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. periodt. 💅

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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)

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💖 DESCRIPTION 💖

so here's the tea ☕ — handles get passed between Fortran and C using an explicit C wrapper to convert Fortran handles into C handles. There is no direct access to C handles in Fortran. Like, none. Don't even try it, bestie.

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 so you can convert from a Fortran handle (which is an integer) to a C handle, and vice versa. It's giving translator, not influencer. 🧚

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. Iconic, consistent, we love to see it. ✨

• 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 💀

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🎀 NOTE 🎀

🚨 important bestie moment 🚨 — this function does not return an error value. Full stop.

Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. Like, undefined undefined. 😭 Don't do it, it's not the vibe.

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📜 Copyright 📜

2003-2026, The Open MPI Community

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and that's the whole page, bestie 🫶 shoutout to the Open MPI girlies for this one, dropped Sep 10, 2026 — go convert your handles responsibly, ily, bye 👑🌸