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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>readv</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="readv"></a> <a name="tag_03_597"></a><!-- readv --> <!--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_597_01"></a>NAME</h4><blockquote>readv - read a vector</blockquote><h4><a name="tag_03_597_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/sys/uio.h.html">sys/uio.h</a>><br><br> ssize_t readv(int</tt> <i>fildes</i><tt>, const struct iovec *</tt><i>iov</i><tt>, int</tt> <i>iovcnt</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_597_03"></a>DESCRIPTION</h4><blockquote><p>The <i>readv</i>() function shall be equivalent to <a href="../functions/read.html"><i>read</i>()</a>, except as describedbelow. The <i>readv</i>() function shall place the input data into the <i>iovcnt</i> buffers specified by the members of the<i>iov</i> array: <i>iov</i>[0], <i>iov</i>[1], ..., <i>iov</i>[ <i>iovcnt</i>-1]. The <i>iovcnt</i> argument is valid if greaterthan 0 and less than or equal to {IOV_MAX}.</p><p>Each <i>iovec</i> entry specifies the base address and length of an area in memory where data should be placed. The<i>readv</i>() function shall always fill an area completely before proceeding to the next.</p><p>Upon successful completion, <i>readv</i>() shall mark for update the <i>st_atime</i> field of the file.</p></blockquote><h4><a name="tag_03_597_04"></a>RETURN VALUE</h4><blockquote><p>Refer to <a href="read.html"><i>read</i>()</a> .</p></blockquote><h4><a name="tag_03_597_05"></a>ERRORS</h4><blockquote><p>Refer to <a href="read.html"><i>read</i>()</a> .</p><p>In addition, the <i>readv</i>() function shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The sum of the <i>iov_len</i> values in the <i>iov</i> array overflowed an <b>ssize_t</b>.</dd></dl><p>The <i>readv</i>() function may fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The <i>iovcnt</i> argument was less than or equal to 0, or greater than {IOV_MAX}.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_597_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_597_06_01"></a>Reading Data into an Array</h5><p>The following example reads data from the file associated with the file descriptor <i>fd</i> into the buffers specified bymembers of the <i>iov</i> array.</p><pre><tt>#include <sys/types.h>#include <sys/uio.h>#include <unistd.h>...ssize_t bytes_read;int fd;char buf0[20];char buf1[30];char buf2[40];int iovcnt;struct iovec iov[3];<br>iov[0].iov_base = buf0;iov[0].iov_len = sizeof(buf0);iov[1].iov_base = buf1;iov[1].iov_len = sizeof(buf1);iov[2].iov_base = buf2;iov[2].iov_len = sizeof(buf2);...iovcnt = sizeof(iov) / sizeof(struct iovec);<br>bytes_read = readv(fd, iov, iovcnt);...</tt></pre></blockquote><h4><a name="tag_03_597_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_597_08"></a>RATIONALE</h4><blockquote><p>Refer to <a href="read.html"><i>read</i>()</a> .</p></blockquote><h4><a name="tag_03_597_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_597_10"></a>SEE ALSO</h4><blockquote><p><a href="read.html"><i>read</i>()</a> , <a href="writev.html"><i>writev</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/sys/uio.h.html"><i><sys/uio.h></i></a></p></blockquote><h4><a name="tag_03_597_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_597_12"></a>Issue 6</h4><blockquote><p>Split out from the <a href="../functions/read.html"><i>read</i>()</a> reference page.</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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