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(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 in-
put 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 ele-
ments, 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 subse-
quently 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++ func-
tions 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
4.1.2 Nov 24, 2021 MPI_Pack(3)
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