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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>ungetc</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_010_256"> </a>NAME</h4><blockquote>ungetc - push byte back into input stream</blockquote><h4><a name = "tag_000_010_257"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="stdio.h.html">stdio.h</a>>int ungetc(int <i>c</i>, FILE *<i>stream</i>);</code></pre></blockquote><h4><a name = "tag_000_010_258"> </a>DESCRIPTION</h4><blockquote>The<i>ungetc()</i>function pushes the byte specified by<i>c</i>(converted to an<b>unsigned char</b>)back onto the input stream pointed to by<i>stream</i>.The pushed-back bytes will be returned by subsequent readson that stream in the reverse order of their pushing.A successful intervening call (with the stream pointed to by<i>stream</i>)to a file-positioning function (.Fn fseek ,<i><a href="fsetpos.html">fsetpos()</a></i>or<i><a href="rewind.html">rewind()</a></i>)discards any pushed-back bytes for the stream.The external storage corresponding to the stream is unchanged.<p>One byte of push-back is guaranteed. If<i>ungetc()</i>is called too many times on the same stream without anintervening read or file-positioning operation on that stream,the operation may fail.<p>If the value of<i>c</i>equals that of the macro EOF, the operation fails and the inputstream is unchanged.<p>A successful call to<i>ungetc()</i>clears the end-of-file indicator for the stream.The value of the file-position indicator for the stream afterreading or discarding all pushed-back bytes will be the sameas it was before the bytes were pushed back.The file-position indicator is decremented by each successfulcall to<i>ungetc()</i>;if its value was 0 before a call, its value is indeterminate after the call.</blockquote><h4><a name = "tag_000_010_259"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>ungetc()</i>returns the byte pushed back after conversion. Otherwise it returns EOF.</blockquote><h4><a name = "tag_000_010_260"> </a>ERRORS</h4><blockquote>No errors are defined.</blockquote><h4><a name = "tag_000_010_261"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_262"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_263"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_264"> </a>SEE ALSO</h4><blockquote><i><a href="fseek.html">fseek()</a></i>,<i><a href="getc.html">getc()</a></i>,<i><a href="fsetpos.html">fsetpos()</a></i>,<i><a href="read.html">read()</a></i>,<i><a href="rewind.html">rewind()</a></i>,<i><a href="setbuf.html">setbuf()</a></i>,<i><a href="stdio.h.html"><stdio.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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