SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Pack_external_size(const char *datarep, int incount,
               MPI_Datatype datatype, MPI_Aint *size)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_PACK_EXTERNAL_SIZE(DATAREP, INCOUNT, DATATYPE, SIZE, IERROR)

               INTEGER         INCOUNT, DATATYPE, IERROR
               INTEGER(KIND=MPI_ADDRESS_KIND) SIZE
               CHARACTER*(*)   DATAREP

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Pack_external_size(datarep, incount, datatype, size, ierror)
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               INTEGER, INTENT(IN) :: incount
               CHARACTER(LEN=*), INTENT(IN) :: datarep
               INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: size
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • datarep: Data representation (string).

       • incount: Number of input data items (integer).

       • datatype: Datatype of each input data item (handle).

OUTPUT PARAMETERS

       • size: Upper bound on size of packed message, in bytes (integer).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION

       MPI_Pack_external_size  allows  the application to find out how much space is needed to pack a message in
       the portable format defined by the MPI Forum. It returns in size an  upper  bound  on  the  increment  in
       position  that  would occur in a call to MPI_Pack_external with the same values for datarep, incount, and
       datatype.

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

NOTES

       The datarep argument specifies the data format. The only valid value in the current  version  of  MPI  is
       “external32”. The argument is provided for future extensibility.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • MPI_Pack_external

          • MPI_Unpack_external

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                         MPI_PACK_EXTERNAL_SIZE(3)