MPI_OP_C2F(3)

💖 MPI_OP_C2F(3) — Open MPI's handle-translator era 💖

okay bestie, gather round, because this one is the glue of Fortran↔C friendships and it's lowkey iconic 🫶

This page covers a whole lil squad of translators: 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</> ✨

and what do they do? they translate a C handle into a Fortran handle, or vice versa. that's it, that's the whole vibe 💅

---

✨ 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)

---

🌈 DESCRIPTION 🌈

so here's the tea, bestie ☕️ Handles get 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, like, none, don't even 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 💫

and the handle translation functions? They're provided in C, obviously, to convert from a Fortran handle (which is an integer, bestie, just an integer) to a C handle, and vice versa 🔁

---

🎀 a lil example because I love you 🎀

say 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 💀
• if comm is an invalid Fortran handle, then MPI_Comm_f2c returns an invalid C handle 😭

no cap, that's the whole contract.

---

⚠️ NOTE ⚠️

ok this part is important so 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, undefined undefined. Feral behaviour. Do not. 🚫

---

📜 Copyright 📜

2003-2026, The Open MPI Community

---

and that's the whole page, bestie — you understood the assignment 💅✨ This lil masterpiece came to you courtesy of Open MPI, dated Sep 10, 2026, and it goes by MPI_OP_C2F(3). mwah 🍓🎀🦋