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MPI_Pack_external_size

:ref:`MPI_Pack_external_size` |mdash| Calculates upper bound on space needed to write to a portable format

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Pack_external_size(const char *datarep, int incount,
     MPI_Datatype datatype, MPI_Aint *size)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_PACK_EXTERNAL_SIZE(DATAREP, INCOUNT, DATATYPE, SIZE, IERROR)

     INTEGER         INCOUNT, DATATYPE, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND) SIZE
     CHARACTER*(*)   DATAREP

Fortran 2008 Syntax

USE mpi_f08
MPI_Pack_external_size(datarep, incount, datatype, size, ierror)
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER, INTENT(IN) :: incount
     CHARACTER(LEN=*), INTENT(IN) :: datarep
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • datarep: Data representation (string).
  • incount: Number of input data items (integer).
  • datatype: Datatype of each input data item (handle).

OUTPUT PARAMETERS

  • size: Upper bound on size of packed message, in bytes (integer).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

:ref:`MPI_Pack_external_size` allows the application to find out how much space is needed to pack a message in the portable format defined by the MPI Forum. It returns in size an upper bound on the increment in position that would occur in a call to :ref:`MPI_Pack_external` with the same values for datarep, incount, and datatype.

The call returns an upper bound, rather than an exact bound, as the exact amount of space needed to pack the message may depend on context and alignment (e.g., the first message packed in a packing unit may take more space).

NOTES

The datarep argument specifies the data format. The only valid value in the current version of MPI is "external32". The argument is provided for future extensibility.

ERRORS

.. seealso::
   * :ref:`MPI_Pack_external`
   * :ref:`MPI_Unpack_external`