MPI_Get_elements(3) Open MPI MPI_Get_elements(3)
NAME
MPI_Get_elements, MPI_Get_elements_x - Returns the number of basic ele-
ments 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
USE MPI
! or the older form: 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
Fortran 2008 Syntax
USE mpi_f08
MPI_Get_elements(status, datatype, count, ierror)
TYPE(MPI_Status), INTENT(IN) :: status
TYPE(MPI_Datatype), INTENT(IN) :: datatype
INTEGER, INTENT(OUT) :: count
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Get_elements_x(status, datatype, count, ierror)
TYPE(MPI_Status), INTENT(IN) :: status
TYPE(MPI_Datatype), INTENT(IN) :: datatype
INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: count
INTEGER, OPTIONAL, INTENT(OUT) :: 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" re-
ceived, 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 re-
turned (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 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.
FORTRAN 77 NOTES
The MPI standard prescribes portable Fortran syntax for the COUNT argu-
ment 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
4.1.2 Nov 24, 2021 MPI_Get_elements(3)
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