MPI_WIN_C2F(3)

💖 MPI_WIN_C2F 💖

okay bestie, welcome to the Open MPI manual — today's page is MPI_WIN_C2F(3), and she's the handle-translation girlie. no cap, if you've ever tried to hand a Fortran thingie over to C code, this is your page. 🦋

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🌸 NAME 🌸

bestie. listen. this page is not ONE function, it's a whole squad of them, all doing the same job for different handle types:

• 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 all do? the way that they exist purely to translate a C handle into a Fortran handle, or vice versa. that's it. that's the whole job. 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 📖

okay so here's the tea. handles get passed between Fortran and C — but not by magic, bestie, by using an explicit C wrapper to convert Fortran handles into C handles. there is no direct access to C handles in Fortran. that's just how it is. 🙈

the type definition MPI_Fint is provided in C, and it's an integer of the size that matches a Fortran INTEGER. usually, MPI_Fint will be equivalent to int. (usually. not always. she's flexible like that. 💅)

so the handle translation functions are provided in C, and they convert from a Fortran handle (which — plot twist — is just an integer) to a C handle, and vice versa. both directions, iconic behaviour. ✨

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 (that's the 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 💀

no vibe check, no error message, it just does the thing. iykyk.

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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. do not do this, bestie, i'm begging. 🫶

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📜 Copyright 📜

2003-2026, The Open MPI Community

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and that's the whole page, slay 💖 this was the Open MPI manual, page MPI_WIN_C2F(3), and she was last updated Sep 10, 2026. go forth and convert ur handles, bestie, u got this 🎀✨🦋🌸