:ref:`MPI_Pack_size` |mdash| Returns the upper bound on the amount of space needed to pack a message.
#include <mpi.h>
int MPI_Pack_size(int incount, MPI_Datatype datatype, MPI_Comm comm,
int *size)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_PACK_SIZE(INCOUNT, DATATYPE, COMM, SIZE, IERROR)
INTEGER INCOUNT, DATATYPE, COMM, SIZE, IERROR
USE mpi_f08
MPI_Pack_size(incount, datatype, comm, size, ierror)
INTEGER, INTENT(IN) :: incount
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(OUT) :: size
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
incount
: Count argument to packing call (integer).datatype
: Datatype argument to packing call (handle).comm
: Communicator argument to packing call (handle).
size
: Upper bound on size of packed message, in bytes (integer).ierror
: Fortran only: Error status (integer).
:ref:`MPI_Pack_size` allows the application to find out how much space is needed to pack a message. A call to MPI_Pack_size(incount, datatype, comm, size) returns in size an upper bound on the increment in position that would occur in a call to :ref:`MPI_Pack`, with the same values for incount, datatype, and comm.
Rationale: The call returns an upper bound, rather than an exact bound, since the exact amount of space needed to pack the message may depend on the context (e.g., first message packed in a packing unit may take more space).
.. seealso::
* :ref:`MPI_Pack`
* :ref:`MPI_Unpack`