MPI_TYPE_C2F(3)

🌸 MPI_TYPE_C2F(3) — from the Open MPI manual 💅

okay bestie, sit down, we're doing handle translations today and it's actually so useful, i promise 🫶

✨ 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. the glow-up is bidirectional ✨

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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)

ngl, those signatures in the mpi-group/mpi-win region are printed exactly like that in the original — MPI Fint, MPI Group and all. i'm not touching a single character of them, bestie. not my job, not my problem 🙈

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💖 DESCRIPTION 💖

so here's the tea ☕ — handles get passed between Fortran and C by using an explicit C wrapper to convert Fortran handles into C handles. that's the ✨only✨ way. there is no direct access to C handles in Fortran. periodt. 💅

the type definition MPI_Fint is provided in C, and it's an integer whose size matches a Fortran INTEGER; usually, MPI_Fint will be equivalent to int. lowkey iconic.

and the handle translation functions? they're provided in C so you can go from a Fortran handle (which is an integer, yes really) to a C handle, and vice versa. it's giving translator bestie. 🦋

for example — and this is the moment, pay attention:

• 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 (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 💀

like… the audacity, but also, fair. garbage in, garbage out, no cap.

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⚠️ NOTE ⚠️

okay this part is important so listen up. this function does not return an error value. consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined. undefined behaviour. not "probably fine". not "it worked on my laptop". undefined. do not do it. i'm begging 🙏

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💜 Copyright 💜

2003-2026, The Open MPI Community

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and that's the whole page, bestie 🎀 thanks for reading all the way through, you ate that fr fr 👑 this was MPI_TYPE_C2F(3) from the Open MPI manual, stamped Sep 10, 2026, copyright 2003-2026, The Open MPI Community — go translate some handles, mwah 💖✨