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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>fgetc</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="fgetc"></a> <a name="tag_03_162"></a><!-- fgetc --> <!--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_162_01"></a>NAME</h4><blockquote>fgetc - get a byte from a stream</blockquote><h4><a name="tag_03_162_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br><br> int fgetc(FILE *</tt><i>stream</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_162_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>If the end-of-file indicator for the input stream pointed to by <i>stream</i> is not set and a next byte is present, the<i>fgetc</i>() function shall obtain the next byte as an <b>unsigned char</b> converted to an <b>int</b>, from the input streampointed to by <i>stream</i>, and advance the associated file position indicator for the stream (if defined). Since <i>fgetc</i>()operates on bytes, reading a character consisting of multiple bytes (or "a multi-byte character") may require multiple calls to<i>fgetc</i>().</p><p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The<i>fgetc</i>() function may mark the <i>st_atime</i> field of the file associated with <i>stream</i> for update. The<i>st_atime</i> field shall be marked for update by the first successful execution of <i>fgetc</i>(), <a href="../functions/fgets.html"><i>fgets</i>()</a>, <a href="../functions/fgetwc.html"><i>fgetwc</i>()</a>, <a href="../functions/fgetws.html"><i>fgetws</i>()</a>, <a href="../functions/fread.html"><i>fread</i>()</a>, <a href="../functions/fscanf.html"><i>fscanf</i>()</a>, <a href="../functions/getc.html"><i>getc</i>()</a>, <a href="../functions/getchar.html"><i>getchar</i>()</a>, <a href="../functions/gets.html"><i>gets</i>()</a>, or <a href="../functions/scanf.html"><i>scanf</i>()</a> using <i>stream</i> that returns data not supplied by a prior call to <a href="../functions/ungetc.html"><i>ungetc</i>()</a> or <a href="../functions/ungetwc.html"><i>ungetwc</i>()</a>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_162_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>fgetc</i>() shall return the next byte from the input stream pointed to by <i>stream</i>. If theend-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream shall beset and <i>fgetc</i>() shall return EOF. If a read error occurs, the error indicator for the stream shall be set, <i>fgetc</i>()shall return EOF, <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> and shall set <i>errno</i> to indicate the error. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_162_05"></a>ERRORS</h4><blockquote><p>The <i>fgetc</i>() function shall fail if data needs to be read and:</p><dl compact><dt>[EAGAIN]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The O_NONBLOCK flag is set for the file descriptor underlying <i>stream</i> and the process would be delayed in the <i>fgetc</i>()operation. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt>[EBADF]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The file descriptor underlying <i>stream</i> is not a valid file descriptor open for reading. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt>[EINTR]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The read operation was terminated due to the receipt of a signal, and no data was transferred. <img src="../images/opt-end.gif"alt="[Option End]" border="0"></dd><dt>[EIO]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Aphysical I/O error has occurred, or the process is in a background process group attempting to read from its controlling terminal,and either the process is ignoring or blocking the SIGTTIN signal or the process group is orphaned. This error may also begenerated for implementation-defined reasons. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt>[EOVERFLOW]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the correspondingstream. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd></dl><p>The <i>fgetc</i>() function may fail if:</p><dl compact><dt>[ENOMEM]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Insufficient storage space is available. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt>[ENXIO]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Arequest was made of a nonexistent device, or the request was outside the capabilities of the device. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_162_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_162_07"></a>APPLICATION USAGE</h4><blockquote><p>If the integer value returned by <i>fgetc</i>() is stored into a variable of type <b>char</b> and then compared against theinteger constant EOF, the comparison may never succeed, because sign-extension of a variable of type <b>char</b> on widening tointeger is implementation-defined.</p><p>The <a href="../functions/ferror.html"><i>ferror</i>()</a> or <a href="../functions/feof.html"><i>feof</i>()</a> functions mustbe used to distinguish between an error condition and an end-of-file condition.</p></blockquote><h4><a name="tag_03_162_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_162_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_162_10"></a>SEE ALSO</h4><blockquote><p><a href="feof.html"><i>feof</i>()</a> , <a href="ferror.html"><i>ferror</i>()</a> , <a href="fopen.html"><i>fopen</i>()</a> , <ahref="getchar.html"><i>getchar</i>()</a> , <a href="getc.html"><i>getc</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/stdio.h.html"><i><stdio.h></i></a></p></blockquote><h4><a name="tag_03_162_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_162_12"></a>Issue 5</h4><blockquote><p>Large File Summit extensions are added.</p></blockquote><h4><a name="tag_03_162_13"></a>Issue 6</h4><blockquote><p>Extensions beyond the ISO C standard are marked.</p><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>The [EIO] and [EOVERFLOW] mandatory error conditions are added.</p></li><li><p>The [ENOMEM] and [ENXIO] optional error conditions are added.</p></li></ul><p>The following changes are made for alignment with the ISO/IEC 9899:1999 standard:</p><ul><li><p>The DESCRIPTION is updated to clarify the behavior when the end-of-file indicator for the input stream is not set.</p></li><li><p>The RETURN VALUE section is updated to note that the error indicator shall be set for the stream.</p></li></ul></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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