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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 |
| “peeking ahead” 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. |
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| <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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