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<a name="FLUSH"></a>
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<p>
Next: <a href="FNUM.html#FNUM" accesskey="n" rel="next">FNUM</a>, Previous: <a href="FLOOR.html#FLOOR" accesskey="p" rel="prev">FLOOR</a>, Up: <a href="Intrinsic-Procedures.html#Intrinsic-Procedures" accesskey="u" rel="up">Intrinsic Procedures</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="FLUSH-_002d_002d_002d-Flush-I_002fO-unit_0028s_0029"></a>
<h3 class="section">9.109 <code>FLUSH</code> &mdash; Flush I/O unit(s)</h3>
<a name="index-FLUSH"></a>
<a name="index-file-operation_002c-flush"></a>

<dl compact="compact">
<dt><em>Description</em>:</dt>
<dd><p>Flushes Fortran unit(s) currently open for output. Without the optional
argument, all units are flushed, otherwise just the unit specified.
</p>
</dd>
<dt><em>Standard</em>:</dt>
<dd><p>GNU extension
</p>
</dd>
<dt><em>Class</em>:</dt>
<dd><p>Subroutine
</p>
</dd>
<dt><em>Syntax</em>:</dt>
<dd><p><code>CALL FLUSH(UNIT)</code>
</p>
</dd>
<dt><em>Arguments</em>:</dt>
<dd><table>
<tr><td width="15%"><var>UNIT</var></td><td width="70%">(Optional) The type shall be <code>INTEGER</code>.</td></tr>
</table>

</dd>
<dt><em>Note</em>:</dt>
<dd><p>Beginning with the Fortran 2003 standard, there is a <code>FLUSH</code>
statement that should be preferred over the <code>FLUSH</code> intrinsic.
</p>
<p>The <code>FLUSH</code> intrinsic and the Fortran 2003 <code>FLUSH</code> statement
have identical effect: they flush the runtime library&rsquo;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>
<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:
</p>
<div class="smallexample">
<pre class="smallexample">  ! Declare the interface for POSIX fsync function
  interface
    function fsync (fd) bind(c,name=&quot;fsync&quot;)
    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=&quot;foo&quot;)

  ! ...
  ! Perform I/O on unit 10
  ! ...

  ! Flush and sync
  flush(10)
  ret = fsync(fnum(10))

  ! Handle possible error
  if (ret /= 0) stop &quot;Error calling FSYNC&quot;
</pre></div>

</dd>
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