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<h3 class="section">12.10 Unreading</h3>

<p><a name="index-peeking-at-input-1001"></a><a name="index-unreading-characters-1002"></a><a name="index-pushing-input-back-1003"></a>
In parser programs it is often useful to examine the next character in
the input stream without removing it from the stream.  This is called
&ldquo;peeking ahead&rdquo; at the input because your program gets a glimpse of
the input it will read next.

   <p>Using stream I/O, you can peek ahead at input by first reading it and
then <dfn>unreading</dfn> it (also called  <dfn>pushing it back</dfn> on the stream). 
Unreading a character makes it available to be input again from the stream,
by  the next call to <code>fgetc</code> or other input function on that stream.

<ul class="menu">
<li><a accesskey="1" href="Unreading-Idea.html#Unreading-Idea">Unreading Idea</a>:               An explanation of unreading with pictures. 
<li><a accesskey="2" href="How-Unread.html#How-Unread">How Unread</a>:                   How to call <code>ungetc</code> to do unreading. 
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