Retrieves attribute value by key


#include "mpi.h"
int MPI_Attr_get ( 
        MPI_Comm comm, 
        int keyval, 
        void *attr_value, 
        int *flag )

Input Parameters

comm communicator to which attribute is attached (handle)
keyval key value (integer)

Output Parameters

attr_value attribute value, unless flag = false
flag true if an attribute value was extracted; false if no attribute is associated with the key


Attributes must be extracted from the same language as they were inserted in with MPI_ATTR_PUT. The notes for C and Fortran below explain why.

Notes for C

Even though the attr_value arguement is declared as void *, it is really the address of a void pointer. See the rationale in the standard for more details.

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.

The attr_value in Fortran is a pointer to a Fortran integer, not a pointer to a void *.


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).
Other error; the error code associated with this error indicates an attempt to use an invalue keyval.