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MPI_Get_elements - Returns the number of basic elements in a data
type.
#include <mpi.h>
int MPI_Get_elements(MPI_Status *status, MPI_Datatype datatype,
int *count)
INCLUDE ’mpif.h’
MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
#include <mpi.h>
int Status::Get_elements(const Datatype& datatype) const
- status
- Return status of receive operation (status).
- datatype
- Datatype used by receive operation (handle).
count
Number of received basic elements (integer).
- IERROR
- Fortran only: Error
status (integer).
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.
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.
MPI_Get_count
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