osx man page for mpi_pack_size

MPI_Pack_size(3OpenMPI) 												   MPI_Pack_size(3OpenMPI)

NAME
       MPI_Pack_size - Returns the upper bound on the amount of space needed to pack a message.

SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Pack_size(int incount, MPI_Datatype datatype, MPI_Comm comm,
	    int *size)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_PACK_SIZE(INCOUNT, DATATYPE, COMM, SIZE, IERROR)
	    INTEGER   INCOUNT, DATATYPE, COMM, SIZE, IERROR

C++ Syntax
       #include <mpi.h>
       int Datatype::Pack_size(int incount, const Comm& comm) const

INPUT PARAMETERS
       incount	 Count argument to packing call (integer).

       datatype  Datatype argument to packing call (handle).

       comm	 Communicator argument to packing call (handle).

OUTPUT PARAMETERS
       size	 Upper bound on size of packed message, in bytes (integer).

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION
       MPI_Pack_size  allows  the  application	to find out how much space is needed to pack a message. A call to MPI_Pack_size(incount, datatype,
       comm, size) returns in size an upper bound on the increment in position that would occur in a call to MPI_Pack, with the  same  values  for
       incount, datatype, and comm.

       Rationale:   The  call  returns	an upper bound, rather than an exact bound, since the exact amount of space needed to pack the message may
       depend on the context (e.g., first message packed in a packing unit may take more space).

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_Pack
       MPI_Unpack

Open MPI 1.2							  September 2006					   MPI_Pack_size(3OpenMPI)