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