MPI_Pack(3)                        Open MPI                        MPI_Pack(3)



NAME
       MPI_Pack - Packs data of a given datatype into contiguous memory.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Pack(void *inbuf, int incount, MPI_Datatype datatype,
            void *outbuf, int outsize, int *position, MPI_Comm comm)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_PACK(INBUF, INCOUNT, DATATYPE, OUTBUF,OUTSIZE, POSITION,
                 COMM, IERROR)
            <type>    INBUF(*), OUTBUF(*)
            INTEGER   INCOUNT, DATATYPE, OUTSIZE, POSITION, COMM, 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




1.4.1                            Jan 14, 2010                      MPI_Pack(3)
