MPI_MESSAGE_F2C(3)

🌸 NAME 🌸

okay bestie, gather round, because this is the whole handle-glow-up squad 💅 — a full roster of translator functions:

• 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 whole collective job description is: Translates a C handle into a Fortran handle, or vice versa.</p> ✨

💫 side quest: the syntax block downstairs also serves MPI_Group_f2c and MPI_Group_c2f. we keep it exactly how the page says it, no cap.

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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)

(yes, we typed the MPI_Group lines exactly as the page has them. character for character. that's the assignment and we do not deviate 😌)

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💅 DESCRIPTION 💅

so here's the tea, bestie ☕: handles get passed between Fortran and C by using an explicit C wrapper to convert Fortran handles into C handles. and the vibe check is — there is no direct access to C handles in Fortran. 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 🌈

and the handle translation functions? those are the ones provided in C to convert from a Fortran handle (which is an integer) to a C handle, and vice versa. 🔁✨

like, 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 (the Fortran value), 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. it's giving you get back what the energy you put in deserved 🦋

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🫶 NOTE 🫶

😭 this function does not return an error value. consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. that's real. don't test it. we do not play with undefined behaviour in this group chat 💀

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🎀 Copyright 🎀

2003-2026, The Open MPI Community

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okay that's the whole page, bestie, you ate that 🍓 and if you ever need the receipts: this one comes to you from Open MPI, dated Sep 10, 2026, and it lives under the name MPI_MESSAGE_F2C(3). mwah 💖👑