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