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<h3 class="section">8.84 <code>FLUSH</code> — Flush I/O unit(s)</h3>
<p><a name="index-FLUSH-614"></a><a name="index-file-operation_002c-flush-615"></a>
<dl>
<dt><em>Description</em>:<dd>Flushes Fortran unit(s) currently open for output. Without the optional
argument, all units are flushed, otherwise just the unit specified.
<br><dt><em>Standard</em>:<dd>GNU extension
<br><dt><em>Class</em>:<dd>Subroutine
<br><dt><em>Syntax</em>:<dd><code>CALL FLUSH(UNIT)</code>
<br><dt><em>Arguments</em>:<dd>
<p><table summary=""><tr align="left"><td valign="top" width="15%"><var>UNIT</var> </td><td valign="top" width="70%">(Optional) The type shall be <code>INTEGER</code>.
<br></td></tr></table>
<br><dt><em>Note</em>:<dd>Beginning with the Fortran 2003 standard, there is a <code>FLUSH</code>
statement that should be preferred over the <code>FLUSH</code> intrinsic.
<p>The <code>FLUSH</code> intrinsic and the Fortran 2003 <code>FLUSH</code> statement
have identical effect: they flush the runtime library's I/O buffer so
that the data becomes visible to other processes. This does not guarantee
that the data is committed to disk.
<p>On POSIX systems, you can request that all data is transferred to the
storage device by calling the <code>fsync</code> function, with the POSIX file
descriptor of the I/O unit as argument (retrieved with GNU intrinsic
<code>FNUM</code>). The following example shows how:
<pre class="smallexample"> ! Declare the interface for POSIX fsync function
interface
function fsync (fd) bind(c,name="fsync")
use iso_c_binding, only: c_int
integer(c_int), value :: fd
integer(c_int) :: fsync
end function fsync
end interface
! Variable declaration
integer :: ret
! Opening unit 10
open (10,file="foo")
! ...
! Perform I/O on unit 10
! ...
! Flush and sync
flush(10)
ret = fsync(fnum(10))
! Handle possible error
if (ret /= 0) stop "Error calling FSYNC"
</pre>
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