MPI_TYPE_F2C(3)

💖 NAME 💖

hey bestie 🫶 welcome to the Open MPI page for the entire little fam of handle translators — the glow-up crew that lives between C and Fortran. 🌈

Say hi to the whole lineup:

• 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 entire job description, no cap: translates a C handle into a Fortran handle, or vice versa. that's the gig, that's the whole vibe 💅

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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 💅

okay so here's the tea 🍓. Handles get passed between Fortran and C by using an explicit C wrapper to convert Fortran handles to C handles. That's the move. There is no direct access to C handles in Fortran — nope, not a thing, don't even try it. 🙈

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, honestly 👑

And the handle translation functions? They're provided in C so you can convert from a Fortran handle (which is an integer, lowkey just a lil number bestie) to a C handle, and vice versa. Both directions, slay. 🦋

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not me giving you an example because examples are the moment. 💜

so like, 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 (that's the Fortran value, bestie), then MPI_Comm_f2c returns a null C handle. and if comm is an invalid Fortran handle, then MPI_Comm_f2c returns an invalid C handle. garbage in, garbage out, the math is mathing ✨

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🫶 NOTE 🫶

⚠️ okay listen up because this part is important: this function does not return an error value. Which means the result of calling it before MPI_Init or after MPI_Finalize is undefined. undefined bestie!! do not do that!! it's giving chaos and not the cute kind 😭

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👑 Copyright 👑

2003-2026, The Open MPI Community

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aaaand that's the whole page, you ate it fr fr 💖 this was MPI_TYPE_F2C(3) from the Open MPI manual, dated Sep 10, 2026. go forth and translate those handles, bestie — you got this 🎀✨🌸