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<title>The GNU Fortran Compiler: FLUSH</title>
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<a name="FLUSH"></a>
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<p>
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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> [<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>
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<a name="FLUSH-_002d_002d_002d-Flush-I_002fO-unit_0028s_0029"></a>
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<h3 class="section">9.102 <code>FLUSH</code> — Flush I/O unit(s)</h3>
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<a name="index-FLUSH"></a>
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<a name="index-file-operation_002c-flush"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p>Flushes Fortran unit(s) currently open for output. Without the optional
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argument, all units are flushed, otherwise just the unit specified.
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</p>
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</dd>
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<dt><em>Standard</em>:</dt>
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<dd><p>GNU extension
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</p>
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</dd>
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<dt><em>Class</em>:</dt>
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<dd><p>Subroutine
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</p>
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</dd>
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<dt><em>Syntax</em>:</dt>
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<dd><p><code>CALL FLUSH(UNIT)</code>
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</p>
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</dd>
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<dt><em>Arguments</em>:</dt>
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<dd><table>
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<tr><td width="15%"><var>UNIT</var></td><td width="70%">(Optional) The type shall be <code>INTEGER</code>.</td></tr>
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</table>
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</dd>
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<dt><em>Note</em>:</dt>
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<dd><p>Beginning with the Fortran 2003 standard, there is a <code>FLUSH</code>
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statement that should be preferred over the <code>FLUSH</code> intrinsic.
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</p>
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<p>The <code>FLUSH</code> intrinsic and the Fortran 2003 <code>FLUSH</code> statement
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have identical effect: they flush the runtime library’s I/O buffer so
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that the data becomes visible to other processes. This does not guarantee
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that the data is committed to disk.
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</p>
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<p>On POSIX systems, you can request that all data is transferred to the
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storage device by calling the <code>fsync</code> function, with the POSIX file
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descriptor of the I/O unit as argument (retrieved with GNU intrinsic
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<code>FNUM</code>). The following example shows how:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> ! Declare the interface for POSIX fsync function
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interface
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function fsync (fd) bind(c,name="fsync")
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use iso_c_binding, only: c_int
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integer(c_int), value :: fd
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integer(c_int) :: fsync
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end function fsync
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end interface
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! Variable declaration
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integer :: ret
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! Opening unit 10
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open (10,file="foo")
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! ...
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! Perform I/O on unit 10
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! ...
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! Flush and sync
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flush(10)
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ret = fsync(fnum(10))
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! Handle possible error
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if (ret /= 0) stop "Error calling FSYNC"
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</pre></div>
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