176 lines
7.3 KiB
HTML
176 lines
7.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>fread</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="fread"></a> <a name="tag_03_185"></a><!-- fread -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_185_01"></a>NAME</h4>
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<blockquote>fread - binary input</blockquote>
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<h4><a name="tag_03_185_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br>
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<br>
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size_t fread(void *restrict</tt> <i>ptr</i><tt>, size_t</tt> <i>size</i><tt>, size_t</tt> <i>nitems</i><tt>,<br>
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FILE *restrict</tt> <i>stream</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_185_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>The <i>fread</i>() function shall read into the array pointed to by <i>ptr</i> up to <i>nitems</i> elements whose size is
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specified by <i>size</i> in bytes, from the stream pointed to by <i>stream</i>. For each object, <i>size</i> calls shall be made to
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the <a href="../functions/fgetc.html"><i>fgetc</i>()</a> function and the results stored, in the order read, in an array of
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<b>unsigned char</b> exactly overlaying the object. The file position indicator for the stream (if defined) shall be advanced by
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the number of bytes successfully read. If an error occurs, the resulting value of the file position indicator for the stream is
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unspecified. If a partial element is read, its value is unspecified.</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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<i>fread</i>() function may mark the <i>st_atime</i> field of the file associated with <i>stream</i> for update. The
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<i>st_atime</i> field shall be marked for update by the first successful execution of <a href=
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"../functions/fgetc.html"><i>fgetc</i>()</a>, <a href="../functions/fgets.html"><i>fgets</i>()</a>, <a href=
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"../functions/fgetwc.html"><i>fgetwc</i>()</a>, <a href="../functions/fgetws.html"><i>fgetws</i>()</a>, <i>fread</i>(), <a href=
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"../functions/fscanf.html"><i>fscanf</i>()</a>, <a href="../functions/getc.html"><i>getc</i>()</a>, <a href=
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"../functions/getchar.html"><i>getchar</i>()</a>, <a href="../functions/gets.html"><i>gets</i>()</a>, or <a href=
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"../functions/scanf.html"><i>scanf</i>()</a> using <i>stream</i> that returns data not supplied by a prior call to <a href=
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"../functions/ungetc.html"><i>ungetc</i>()</a> or <a href="../functions/ungetwc.html"><i>ungetwc</i>()</a>. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_185_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>fread</i>() shall return the number of elements successfully read which is less than
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<i>nitems</i> only if a read error or end-of-file is encountered. If <i>size</i> or <i>nitems</i> is 0, <i>fread</i>() shall return
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0 and the contents of the array and the state of the stream remain unchanged. Otherwise, if a read error occurs, the error
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indicator for the stream shall be set, <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif"
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alt="[Option Start]" border="0"> and <i>errno</i> shall be set to indicate the error. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_185_05"></a>ERRORS</h4>
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<blockquote>
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<p>Refer to <a href="fgetc.html"><i>fgetc</i>()</a> .</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_185_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_185_06_01"></a>Reading from a Stream</h5>
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<p>The following example reads a single element from the <i>fp</i> stream into the array pointed to by <i>buf</i>.</p>
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<pre>
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<tt>#include <stdio.h>
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...
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size_t bytes_read;
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char buf[100];
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FILE *fp;
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...
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bytes_read = fread(buf, sizeof(buf), 1, fp);
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...
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_185_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <a href="../functions/ferror.html"><i>ferror</i>()</a> or <a href="../functions/feof.html"><i>feof</i>()</a> functions must
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be used to distinguish between an error condition and an end-of-file condition.</p>
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<p>Because of possible differences in element length and byte ordering, files written using <a href=
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"../functions/fwrite.html"><i>fwrite</i>()</a> are application-dependent, and possibly cannot be read using <i>fread</i>() by a
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different application or by the same application on a different processor.</p>
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</blockquote>
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<h4><a name="tag_03_185_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_185_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_185_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="feof.html"><i>feof</i>()</a> , <a href="ferror.html"><i>ferror</i>()</a> , <a href="fgetc.html"><i>fgetc</i>()</a> , <a
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href="fopen.html"><i>fopen</i>()</a> , <a href="getc.html"><i>getc</i>()</a> , <a href="gets.html"><i>gets</i>()</a> , <a href=
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"scanf.html"><i>scanf</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/stdio.h.html"><i><stdio.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_185_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_185_12"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The following changes are made for alignment with the ISO/IEC 9899:1999 standard:</p>
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<ul>
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<li>
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<p>The <i>fread</i>() prototype is updated.</p>
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</li>
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<li>
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<p>The DESCRIPTION is updated to describe how the bytes from a call to <a href="../functions/fgetc.html"><i>fgetc</i>()</a> are
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stored.</p>
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</li>
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</ul>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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