.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Pack_external_size 3 "Sep 30, 2023" "4.1.6" "Open MPI"

.SH NAME
\fBMPI_Pack_external_size\fP \- Calculates upper bound on space needed
to write to a portable format

.SH SYNTAX
.ft R

.SH C Syntax
.nf
#include <mpi.h>
int MPI_Pack_external_size(char *\fIdatarep\fP, int \fIincount\fP,
	MPI_Datatype \fIdatatype\fP, MPI_Aint *\fIsize\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_PACK_EXTERNAL_SIZE(\fIDATAREP, INCOUNT, DATATYPE, SIZE, IERROR\fP)

	INTEGER		\fIINCOUNT, DATATYPE, IERROR\fP
	INTEGER(KIND=MPI_ADDRESS_KIND) \fISIZE\fP
	CHARACTER*(*)	\fIDATAREP\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Pack_external_size(\fIdatarep\fP, \fIincount\fP, \fIdatatype\fP, \fIsize\fP, \fIierror\fP)
	TYPE(MPI_Datatype), INTENT(IN) :: \fIdatatype\fP
	INTEGER, INTENT(IN) :: \fIincount\fP
	CHARACTER(LEN=*), INTENT(IN) :: \fIdatarep\fP
	INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: \fIsize\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
MPI::Aint MPI::Datatype::Pack_external_size(const char* \fIdatarep\fP,
	int \fIincount\fP) const

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
datarep
Data representation (string).
.TP 1i
incount
Number of input data items (integer).
.TP 1i
datatype
Datatype of each input data item (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
size
Upper bound on size of packed message, in bytes (integer).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
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 \fIsize\fP an upper bound on the
increment in \fIposition\fP that would occur in a call to
MPI_Pack_external with the same values for \fIdatarep\fP,
\fIincount\fP, and \fIdatatype\fP.
.sp
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).

.SH NOTES
.ft R
The \fIdatarep\fP argument specifies the data format. The only valid
value in the current version of MPI is "external32". The argument is
provided for future extensibility.

.SH ERRORS
.ft R
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.
.sp
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.
.sp
See the MPI man page for a full list of MPI error codes.

.SH SEE ALSO
.ft R
.nf
MPI_Pack_external
MPI_Unpack_external