.\"Copyright 2006, Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_File_iwrite_at 3OpenMPI "September 2006" "Open MPI 1.2" " "
.SH NAME
\fBMPI_File_iwrite_at\fP \- Writes a file at an explicitly specified offset (nonblocking, noncollective).

.SH SYNTAX
.ft R
.nf
C Syntax
    #include <mpi.h>
    int MPI_File_iwrite_at(MPI_File \fIfh\fP, MPI_Offset \fIoffset\fP, 
    	      void \fI*buf\fP, int \fIcount\fP, MPI_Datatype \fIdatatype\fP, MPI_Request \fI*request\fP)

Fortran Syntax (see FORTRAN 77 NOTES)
    INCLUDE 'mpif.h'
    MPI_FILE_IWRITE_AT(\fIFH\fP, \fIOFFSET\fP, \fIBUF\fP, \fICOUNT\fP, \fIDATATYPE\fP, \fIREQUEST\fP, \fIIERROR\fP)
        	<type> \fIBUF\fP(*)
        	INTEGER	\fIFH, COUNT, DATATYPE, REQUEST, IERROR\fP
		INTEGER(KIND=MPI_OFFSET_KIND) \fIOFFSET\fP

.SH C++ Syntax
.nf
#include <mpi.h>
MPI::Request MPI::File::Iwrite_at(MPI::Offset \fIoffset\fP, const void* \fIbuf\fP,
	int \fIcount\fP, const MPI::Datatype& \fIdatatype\fP)

.SH INPUT/OUTPUT PARAMETER
.ft R
.TP 1i
fh    
File handle (handle).

.SH INPUT PARAMETERS
.ft R
.TP 1i
offset
File offset (integer).
.ft R
.TP 1i
buf
Initial address of buffer (choice).
.ft R
.TP 1i
count
Number of elements in buffer (integer).
.ft R
.TP 1i
datatype
Data type of each buffer element (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
request
Request object (handle).
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
MPI_File_iwrite_at is a nonblocking version of MPI_File_write_at. It attempts to write into the file associated with 
.I fh
(at the 
.I offset 
position) a total number of 
.I count 
data items having
.I datatype 
type from the user's buffer 
.I buf.
The offset is in 
.I etype
units relative to the current view. That is, holes are not counted
when locating an offset. The data is written into those parts of the
file specified by the current view. MPI_File_iwrite_at stores the
number of 
.I datatype 
elements actually written in 
.I status. 
All other fields of 
.I status 
are undefined. The request structure can be passed to MPI_Wait or MPI_Test, which will return a status with the number of bytes actually accessed. 
.sp
It is erroneous to call this function if MPI_MODE_SEQENTIAL mode was specified when the file was open. 

.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fIOFFSET\fP argument only for Fortran 90.  FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_OFFSET_KIND \fIOFFSET\fP
.fi
.sp
where MPI_OFFSET_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH 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.
.sp
Before the error value is returned, the current MPI error handler is
called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.  

' @(#)MPI_File_iwrite_at.3 1.22 06/03/09