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

4.1.6                                             Sep 30, 2023                                       MPI_Pack(3)