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<title>17.7.3 Reading from a device  </title>

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<h3>
  <a name="1204585"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">17.7.3 	 Reading from a device</font>
</h3>


<p>
  <a name="1204586"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Data may be read from the opened device with either the ANSI call, for example:</font>
</p>


<a name="1204587"> </a><font size=2 face=Courier><strong>int size = fread(buffer, x, y, f);<br></strong></font>



<p>
  <a name="1204588"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">or the POSIX call, for example:</font>
</p>


<a name="1204589"> </a><font size=2 face=Courier><strong>int size = read(fd, buffer, 256);<br></strong></font>



<p>
  <a name="1204590"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">which call:</font>
</p>


<a name="1204591"> </a><font size=2 face=Courier><strong>my_device_read(handle, buffer, 256);<br></strong></font>



<p>
  <a name="1204592"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">where <font size=2 face=Courier><strong>handle</strong></font> is the value returned from the open callback. The value returned by the read callback is returned by <font size=2 face=Courier><strong>read</strong></font>.</font>
</p>


<p>
  <a name="1204593"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><em>Note:	 When the ANSI calls are used, buffering may occur in the ANSI libraries. As a result, the relevant device callback may not get called for each call to the ANSI function such as <font size=2 face=Courier><strong>fread()</strong></font> or <font size=2 face=Courier><strong>fwrite()</strong></font>.</em></font>
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<p>
  <a name="1204597"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">In the example used in <a href="posix10.htm#1204562"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>Section

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