MPI_GROUP_C2F(3)

🌸 MPI_GROUP_C2F(3) — Open MPI, bestie edition 🎀

okay so this page is literally your whole translation dictionary between C handles and Fortran handles, brought to you by the Open MPI girlies ✨

The actual stars of the show are all of these cuties:

• 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 collective job? Translates a C handle into a Fortran handle, or vice versa. no cap, that's the whole gig 💅

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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, MPI Fint group and MPI Group group are written exactly like that up there — I'm not touching them, that's canon, iykyk 🙈)

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💖 DESCRIPTION 💖

So here's the tea 🍓: handles get passed between Fortran and C by using an explicit C wrapper to convert Fortran handles into C handles. and listen — there is no direct access to C handles in Fortran. periodt. that's just not a thing, don't 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. 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. iconic behavior honestly 👑

For example — picture this 🌈 — 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. three moods, one function 💀

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⭐ NOTE ⭐

🚨 okay bestie pay attention: this function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. like, literally undefined. don't be that girl 😭

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

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and that's the whole page, mwah 💋 — brought to you by Open MPI, dated Sep 11, 2026, page MPI_GROUP_C2F(3), slay ✨🫶