.\" -*- nroff -*-
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Comm_f2c 3 "Sep 30, 2023" "4.1.6" "Open MPI"
.SH NAME
\fBMPI_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 \fP \- Translates a C handle into a Fortran handle, or vice versa.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
MPI_Comm MPI_Comm_f2c(MPI_Fint \fIcomm\fP)
MPI_Fint MPI_Comm_c2f(MPI_Comm \fIcomm\fP)

MPI_File MPI_File_f2c(MPI_Fint \fIfile\fP)
MPI_Fint MPI_File_c2f(MPI_File \fIfile\fP)

MPI_Group MPI_Group_f2c(MPI Fint \fIgroup\fP)
MPI_Fint MPI_Group_c2f(MPI Group \fIgroup\fP)

MPI_Info MPI_Info_f2c(MPI_Fint \fIinfo\fP)
MPI_Fint MPI_Info_c2f(MPI_Info \fIinfo\fP)

MPI_Message MPI_Message_f2c(MPI_Fint \fImessage\fP)
MPI_Fint MPI_Message_c2f(MPI_Message \fImessage\fP)

MPI_Op MPI_Op_f2c(MPI_Fint \fIop\fP)
MPI_Fint MPI_Op_c2f(MPI_Op \fIop\fP)

MPI_Request MPI_Request_f2c(MPI_Fint \fIrequest\fP)
MPI_Fint MPI_Request_c2f(MPI_Request \fIrequest\fP)

MPI_Datatype MPI_Type_f2c(MPI_Fint \fIdatatype\fP)
MPI_Fint MPI_Type_c2f(MPI_Datatype \fIdatatype\fP)

MPI_Win MPI_Win_f2c(MPI_Fint \fIwin\fP)
MPI_Fint MPI_Win_c2f(MPI_Win \fIwin\fP)

.fi
.SH DESCRIPTION
.ft R
Handles are passed between Fortran and C or C++ by using an explicit C wrapper to convert Fortran handles to C handles. There is no direct access to C or C++ handles in Fortran. Handles are passed between C and C++ using overloaded C++ operators called from C++ code. There is no direct access to C++ objects from C. The type definition \fIMPI_Fint\fP is provided in C/C++ for an integer of the size that matches a Fortran \fIINTEGER\fP; usually, \fIMPI_Fint\fP will be equivalent to \fIint\fP. 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.
.PP
For example, if \fIcomm\fP is a valid Fortran handle to a communicator, then MPI_Comm_f2c returns a valid C handle to that same communicator; if \fIcomm\fP = MPI_COMM_NULL (Fortran value), then MPI_Comm_f2c returns a null C handle; if \fIcomm\fP is an invalid Fortran handle, then MPI_Comm_f2c returns an invalid C handle.
.SH NOTE
This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined.