MPI_COMM_C2F(3)

💖 NAME 💖

okay so welcome to the MPI_COMM_C2F(3) page from the Open MPI manual — this is literally the handle-translation main character moment, and lowkey it ate. The whole 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, MPI_Win_c2f — translates a C handle into a Fortran handle, or vice versa. periodt 💅

✨ 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)

iykyk: these signatures are the whole plot, bestie 🫶

🦋 DESCRIPTION 🦋

okay so the concept is giving bilingual bestie: 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. 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. 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.

not me being obsessed with this, but the example is lowkey the vibe check:

• 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 “translate me, i'm famous” energy fr fr 🦋

🎀 NOTE 🎀

⚠️ important, no cap: this function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. highkey do not play with that, bestie 💀

👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

---

mwah 💋 — page MPI_COMM_C2F(3) from Open MPI, dated Sep 11, 2026; slay, stay hydrated, and may your handles always translate, bestie 🫶✨