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 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 inte-
gral 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 func-
tions 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++ func-
tions 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)
