MPI_REQUEST_F2C(3)

💖 NAME 💖

okay so bestie, say hi to the whole handshake squad 👑 — this is the MPI_REQUEST_F2C(3) page from the Open MPI manual (section 3, iykyk).

Here's everybody on the roster:

• 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, you ask? ✨ Translates a C handle into a Fortran handle, or vice versa. That's the whole job. Glow-up for handles. 💅

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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 ☕: when handles travel between Fortran and C, they don't just waltz across the border on their own. You use an explicit C wrapper to convert Fortran handles into C handles. That's the move. And in Fortran? There is no direct access to C handles in Fortran. None. 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. Cute, right? 🎀

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. Equality. Balance. Main character energy on both sides. ✨

Okay, example time, because vibes alone won't save you:

• 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

That's it. That's the translation. No notes. 💅

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⚠️ NOTE ⚠️

bestie, listen. This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. Under. Fined. 💀 Not "probably fine", not "it worked on my laptop" — undefined. 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, bestie 🎀 Open MPI, dated Sep 10, 2026, filed squarely under MPI_REQUEST_F2C(3). go convert some handles, you got this. mwah. 💖✨🌸