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<title>17.8 Redirecting streams</title>

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<h2>
  <a name="1204671"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">17.8 	 Redirecting streams</font>
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<p>
  <a name="1204672"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Is is often desirable to redirect I/O streams such as <font size=2 face=Courier><strong>stdin</strong></font>, <font size=2 face=Courier><strong>stdout</strong></font> and <font size=2 face=Courier><strong>stderr</strong></font> to a new device. By the time <font size=2 face=Courier><strong>main()</strong></font> is called, these have already been attached to the <font size=2 face=Courier><strong>dcu</strong></font> device. However, as no data has been buffered at this point, it is safe to change which device is associated with the file descriptor which a <font size=2 face=Courier><strong>FILE</strong></font> stream uses. A call to <font size=2 face=Courier><strong>dup()</strong></font> allocates the numerically lowest free file descriptor, so closing a file immediately prior to calling <font size=2 face=Courier><strong>dup()</strong></font> causes its file descriptor to be reused. The following example illustrates this property for redirecting <font size=2 face=Courier><strong>stdout</strong></font> to a new device.</font>
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  <a name="1204673"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Example:</font>
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<a name="1204674"> </a><font size=2 face=Courier><strong>int fd = open("asc0:",O_RDWR);<br>close(1);

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