MPI_MESSAGE_C2F(3)

okay bestie, pull up a chair 🎀 this is the Open MPI manual page for MPI_MESSAGE_C2F(3), and it's literally a whole family of little translator functions that pass handles back and forth between Fortran-land and C-land. Cute, right? It's giving bilingual icon energy.

Here's the whole squad (they all do the same ✨ translate-y thing ✨), and yes, some of them have their own pages:

• 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? Translates a C handle into a Fortran handle, or vice versa. 💅

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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 whole move. And bestie, there is no direct access to C handles in Fortran — you gotta go through the wrapper, no shortcuts, 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. Slay, consistent sizing. 🌈

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. Literally just vibes conversion, both directions. 🔁

For example — and bestie this example eats, fr fr — 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's giving exactly-what-you-put-in energy. 🪩

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🚨 NOTE 🚨

⚠️ bestie, listen up, this one's important: This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. Not "kinda weird", not "probably fine" — undefined. Don't do it. That's a villain arc you don't need. 💀

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📜 Copyright

2003-2026, The Open MPI Community 🫶

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and that's the whole page, bestie!! 💜 this manual page comes to you from the Open MPI girlies, dated Sep 10, 2026, and it lives at the name MPI_MESSAGE_C2F(3). go forth and translate those handles, you absolute queen. 👑✨