MPI_INFO_C2F(3)

✨ NAME ✨

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 — Translates a C handle into a Fortran handle, or vice versa.

okay bestie so this is the Open MPI era of handle translation 💅 it's the whole squad of _f2c and _c2f functions, one glorious little bridge between your C code and your Fortran code, and honestly? iconic. 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)

🫶 friendly heads up: those two MPI_Group lines are copied character for character from the original, spaces in MPI Fint and MPI Group and all. not me being sloppy — that's just what it says, fr.

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💖 DESCRIPTION 💖

So here's the tea ☕ — handles get passed between Fortran and C using an explicit C wrapper that converts Fortran handles into C handles. There is no direct access to C handles in Fortran. none. zero. that door is locked 🔒

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. it's giving "size-matched bestie" energy.

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. that's the whole job. that's the assignment. and they ate. 💅

For example — and bestie this example is load-bearing so stay with me:

• 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 💀 (it does not fix it. it does not warn you. it just hands you garbage back and walks away)

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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. and when we say undefined we mean UNDEFINED — no error code, no safety net, no little angel on your shoulder. call it too early or too late and you're on your own, bestie 🙈

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📜 Copyright

2003-2026, The Open MPI Community

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and that's the whole page, periodt 🎀 tysm for reading this far, you're genuinely the main character of this build. this lil' cutie is from the Open MPI crew and it's dated Sep 10, 2026 — go convert some handles and slay 💜🦋