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MPI_Get_count.3.rst

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MPI_Get_count

:ref:`MPI_Get_count` - Gets the number of top-level elements received.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Get_count(const MPI_Status *status, MPI_Datatype datatype,
    int *count)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_GET_COUNT(STATUS, DATATYPE, COUNT, IERROR)
    INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR

Fortran 2008 Syntax

USE mpi_f08

MPI_Get_count(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

INPUT PARAMETERS

  • status : Return status of receive operation (status).
  • datatype : Datatype of each receive buffer element (handle).

OUTPUT PARAMETERS

  • count : Number of received elements (integer).
  • ierror : Fortran only: Error status (integer).

DESCRIPTION

Returns the number of entries received. (We count entries, each of type datatype, not bytes.) The datatype argument should match the argument provided by the receive call that set the status variable. (As explained in Section 3.12.5 in the MPI-1 Standard, "Use of General Datatypes in Communication," :ref:`MPI_Get_count` may, in certain situations, return the value MPI_UNDEFINED.)

The datatype argument is passed to :ref:`MPI_Get_count` to improve performance. A message might be received without counting the number of elements it contains, and the count value is often not needed. Also, this allows the same function to be used after a call to :ref:`MPI_Probe`.

NOTES

If the size of the datatype is zero, this routine will return a count of zero. If the amount of data in status is not an exact multiple of the size of datatype (so that count would not be integral), a count of MPI_UNDEFINED is returned instead.

ERRORS

If the value to be returned is larger than can fit into the count parameter, an MPI_ERR_TRUNCATE error is raised.

.. seealso:: :ref:`MPI_Get_elements`