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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>ungetc</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="ungetc"></a> <a name="tag_03_800"></a><!-- ungetc --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_800_01"></a>NAME</h4><blockquote>ungetc - push byte back into input stream</blockquote><h4><a name="tag_03_800_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br><br> int ungetc(int</tt> <i>c</i><tt>, FILE *</tt><i>stream</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_800_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i>ungetc</i>() function shall push the byte specified by <i>c</i> (converted to an <b>unsigned char</b>) back onto theinput stream pointed to by <i>stream</i>. The pushed-back bytes shall be returned by subsequent reads on that stream in the reverseorder of their pushing. A successful intervening call (with the stream pointed to by <i>stream</i>) to a file-positioning function( <a href="../functions/fseek.html"><i>fseek</i>()</a>, <a href="../functions/fsetpos.html"><i>fsetpos</i>()</a>, or <a href="../functions/rewind.html"><i>rewind</i>()</a>) shall discard any pushed-back bytes for the stream. The external storagecorresponding to the stream shall be unchanged.</p><p>One byte of push-back shall be provided. If <i>ungetc</i>() is called too many times on the same stream without an interveningread or file-positioning operation on that stream, the operation may fail.</p><p>If the value of <i>c</i> equals that of the macro EOF, the operation shall fail and the input stream shall be leftunchanged.</p><p>A successful call to <i>ungetc</i>() shall clear the end-of-file indicator for the stream. The value of the file-positionindicator for the stream after reading or discarding all pushed-back bytes shall be the same as it was before the bytes were pushedback. The file-position indicator is decremented by each successful call to <i>ungetc</i>(); if its value was 0 before a call, itsvalue is unspecified after the call.</p></blockquote><h4><a name="tag_03_800_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>ungetc</i>() shall return the byte pushed back after conversion. Otherwise, it shall returnEOF.</p></blockquote><h4><a name="tag_03_800_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_800_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_800_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_800_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_800_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_800_10"></a>SEE ALSO</h4><blockquote><p><a href="fseek.html"><i>fseek</i>()</a> , <a href="getc.html"><i>getc</i>()</a> , <a href="fsetpos.html"><i>fsetpos</i>()</a> ,<a href="read.html"><i>read</i>()</a> , <a href="rewind.html"><i>rewind</i>()</a> , <a href="setbuf.html"><i>setbuf</i>()</a> , theBase Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/stdio.h.html"><i><stdio.h></i></a></p></blockquote><h4><a name="tag_03_800_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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