NAME

       MPI_Get_elements  - Returns the number of basic elements in a data type.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Get_elements(MPI_Status *status, MPI_Datatype datatype,
            int *count)

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR

C++ Syntax

       #include <mpi.h>
       int Status::Get_elements(const Datatype& datatype) const

INPUT PARAMETERS

       status    Return status of receive operation (status).

       datatype  Datatype used by receive operation (handle).

OUTPUT PARAMETERS

       count     Number of received basic elements (integer).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_Get_elements  behaves  different from MPI_Get_count, which returns the number of "top-
       level entries" received, i.e., the number of "copies" of type datatype. MPI_Get_count  may
       return  any  integer  value k, where 0 =< k =< count. If MPI_Get_count returns k, then the
       number of basic elements received (and the value returned by  MPI_Get_elements) is n *  k,
       where  n  is  the  number  of basic elements in the type map of datatype. If the number of
       basic elements received is not a multiple of n, that is, if the receive operation has  not
       received  an  integral  number  of datatype "copies," then MPI_Get_count returns the value
       MPI_UNDEFINED.

       Example: Usage of MPI_Get_count and MPI_Get_element:

         ...
         CALL MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr)
         CALL MPI_TYPE_COMMIT(Type2, ierr)
         ...
         CALL MPI_COMM_RANK(comm, rank, ierr)
         IF(rank.EQ.0) THEN
               CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr)
               CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr)
         ELSE
               CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
               CALL MPI_GET_COUNT(stat, Type2, i, ierr)     ! returns i=1
               CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr)  ! returns i=2
               CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
               CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED
               CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr)  ! returns i=3
         END IF

       The function MPI_Get_elements can also be used  after  a  probe  to  find  the  number  of
       elements   in   the  probed  message.  Note  that  the  two  functions  MPI_Get_count  and
       MPI_Get_elements return the same values when they are used with primitive data types.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI:Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Get_count