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MPI_Get_elements(3OpenMPI)                                                        MPI_Get_elements(3OpenMPI)



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  inte-ger integer
       ger  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  ele-
       ments  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




Open MPI 1.2                                   September 2006                     MPI_Get_elements(3OpenMPI)