MPI_Pack(3)

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
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