MPI_WIN_F2C(3)

💖 NAME 💖

bestie, this whole page is about translating handles back and forth between C and Fortran, and here's the full squad of them:

• 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 the whole gig, one job, they ate 💅

This is MPI_WIN_F2C(3) from the Open MPI manual, btw, so you know it's the real deal.

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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)

(and yes, the MPI_Group pair up there really is written like that in the source, we don't fix canon in this house 💀)

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🦋 DESCRIPTION 🦋

okay so here's the tea ☕ — 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, periodt, that door is just not open.

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. Like, it's giving "same energy, different font" ✨

And 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. Both directions, no cap 🫶

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.

so like — valid in, valid out; null in, null out; invalid in, invalid out. the function literally matches your energy every single time 🌸

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💀 NOTE 💀

🚨 big one, bestie 🚨 This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. Not "probably fine", not "works on my machine" — undefined. Do not test it. Do not poke it. It will not text back 😭

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👑 Copyright 👑

2003-2026, The Open MPI Community

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okay that's the whole page, you're so welcome 💖 Open MPI, page MPI_WIN_F2C(3), dated Sep 10, 2026 — go forth and translate those handles, mwah 🎀🦋✨