MPI_MESSAGE_F2C(3)

💖 NAME 💖

okay so this is the MPI_MESSAGE_F2C(3) page from Open MPI, and it is literally the handle-translation bestie page. The whole vibe: translates a C handle into a Fortran handle, or vice versa. periodt 💅

The top-line squad is 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, and MPI_Win_c2f. also lowkey don't forget MPI_Group_f2c and MPI_Group_c2f — they show up in the SYNTAX below, so they are 100% part of the group chat too 🫶

---

🛠️ SYNTAX 🛠️

🧑‍💻 C Syntax 🧑‍💻

here is the C syntax exactly as written, character for character — do not “fix” the MPI Fint / MPI Group moment, bestie, it is literally in the page:

#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)

---

🌸 DESCRIPTION 🌸

Handles are passed between Fortran and C by using an explicit C wrapper to convert Fortran handles to C handles. There is no direct access to C handles in Fortran. no cap, that is just how it is.

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 little type match-up, honestly 💖

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. f2c, c2f, the whole bidirectional slay ✨

Example time, because the vibe check matters: 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. literally the exact translation behavior, bestie 🌈

---

⚠️ NOTE ⚠️

This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined.

so like, no error value to catch, and calling it before MPI_Init or after MPI_Finalize is undefined — undefined is undefined, bestie, respect the window 😭💀

---

📜 COPYRIGHT 📜

2003-2026, The Open MPI Community

okay that is the whole MPI_MESSAGE_F2C(3) page from Open MPI, dated Sep 11, 2026 — footer handled, copyright line included, mwah 💖✨🦋