NAME

       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

C++ Syntax

       #include <mpi.h>
       void Datatype::Pack(const void* inbuf, int incount, void *outbuf,
            int outsize, int& position, const Comm &comm) const

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  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 MPI_Pack:

           int 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

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument. C++ functions 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.

SEE ALSO

       MPI_Unpack
       MPI_Pack_size