NAME

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

SYNTAX

C Syntax

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

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
       MPI_GET_ELEMENTS_X(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE
               INTEGER(KIND=MPI_COUNT_KIND) COUNT
               INTEGER 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 and MPI_Get_elements_x behave 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 and MPI_Get_elements_x) 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. For both functions, if the
       count parameter cannot express the value to be returned (e.g., if  the  parameter  is  too
       small to hold the output value), it is set to 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.

FORTRAN 77 NOTES

       The  MPI  standard  prescribes  portable  Fortran  syntax  for  the  COUNT   argument   of
       MPI_Get_elements_x only for Fortran 90. FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_COUNT_KIND COUNT

       where  MPI_COUNT_KIND is a constant defined in mpif.h and gives the length of the declared
       integer in bytes.

SEE ALSO

       MPI_Get_count