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MPI_Pack.3.rst

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MPI_Pack

:ref:`MPI_Pack` - Packs data of a given datatype into contiguous memory.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Pack(const void *inbuf, int incount, MPI_Datatype datatype,
     void *outbuf, int outsize, int *position, MPI_Comm comm)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_PACK(INBUF, INCOUNT, DATATYPE, OUTBUF,OUTSIZE, POSITION,
             COMM, IERROR)
     <type>  INBUF(*), OUTBUF(*)
     INTEGER INCOUNT, DATATYPE, OUTSIZE, POSITION, COMM, IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Pack(inbuf, incount, datatype, outbuf, outsize, position, comm, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN) :: inbuf
     TYPE(*), DIMENSION(..) :: outbuf
     INTEGER, INTENT(IN) :: incount, outsize
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER, INTENT(INOUT) :: position
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • inbuf: Input buffer start (choice).
  • incount: Number of input data items (integer).
  • datatype: Datatype of each input data item (handle).
  • outsize: Output buffer size, in bytes (integer).
  • comm: Communicator for packed message (handle).

INPUT/OUTPUT PARAMETER

  • position: Current position in buffer, in bytes (integer).

OUTPUT PARAMETERS

  • outbuf: Output buffer start (choice).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

Packs the message in the send buffer specified by inbuf, incount, datatype into the buffer space specified by outbuf and outsize. The input buffer can be any communication buffer allowed in :ref:`MPI_Send`. The output buffer is a contiguous storage area containing outsize bytes, starting at the address outbuf (length is counted in bytes, not elements, as if it were a communication buffer for a message of type MPI_Packed).

The input value of position is the first location in the output buffer to be used for packing. position is incremented by the size of the packed message, and the output value of position is the first location in the output buffer following the locations occupied by the packed message. The comm argument is the communicator that will be subsequently used for sending the packed message.

Example: An example using :ref:`MPI_Pack`:

int myrank, position, i, j, a[2];
char buff[1000];

// ...

MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
if (myrank == 0) {
  /* SENDER CODE */
  position = 0;
  MPI_Pack(&i, 1, MPI_INT, buff, 1000, &position, MPI_COMM_WORLD);
  MPI_Pack(&j, 1, MPI_INT, buff, 1000, &position, MPI_COMM_WORLD);
  MPI_Send(buff, position, MPI_PACKED, 1, 0, MPI_COMM_WORLD);
} else {
  /* RECEIVER CODE */
  MPI_Recv(a, 2, MPI_INT, 0, 0, MPI_COMM_WORLD);
}

ERRORS

.. seealso::
   * :ref:`MPI_Unpack`
   * :ref:`MPI_Pack_size`