Accesses the group associated with given communicator


#include "mpi.h"
int MPI_Comm_group ( 
        MPI_Comm comm, 
        MPI_Group *group )

Input Parameter


Output Parameter

Group in communicator

Using 'MPI_COMM_NULL' with 'MPI_Comm_group'

It is an error to use MPI_COMM_NULL as one of the arguments to MPI_Comm_group. The relevant sections of the MPI standard are

.(2.4.1 Opaque Objects) A null handle argument is an erroneous IN argument in MPI calls, unless an exception is explicitly stated in the text that defines the function.

.(5.3.2. Group Constructors) <no text in MPI_COMM_GROUP allowing a null handle>

Previous versions of MPICH allow MPI_COMM_NULL in this function. In the interests of promoting portability of applications, we have changed the behavior of MPI_Comm_group to detect this violation of the MPI standard.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

No error; MPI routine completed successfully.
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).