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<center><font size="2">The Open Group Base Specifications Issue 6<br>
IEEE Std 1003.1-2001<br>
Copyright &copy; 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<hr size="2" noshade>
<h4><a name="tag_13_68_01"></a>NAME</h4>
<blockquote>sys/uio.h - definitions for vector I/O operations</blockquote>
<h4><a name="tag_13_68_02"></a>SYNOPSIS</h4>
<blockquote class="synopsis">
<div class="box"><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../../images/opt-start.gif" alt=
"[Option Start]" border="0"> #include &lt;sys/uio.h&gt; <img src="../../images/opt-end.gif" alt="[Option End]" border=
"0"></tt></div>
</blockquote>
<h4><a name="tag_13_68_03"></a>DESCRIPTION</h4>
<blockquote>
<p>The <i>&lt;sys/uio.h&gt;</i> header shall define the <b>iovec</b> structure that includes at least the following members:</p>
<pre>
<tt>void *iov_base </tt> Base address of a memory region for input or output. <tt>
size_t iov_len </tt> The size of the memory pointed to by <i>iov_base.</i> <tt>
</tt>
</pre>
<p>The <i>&lt;sys/uio.h&gt;</i> header uses the <b>iovec</b> structure for scatter/gather I/O.</p>
<p>The <b>ssize_t</b> and <b>size_t</b> types shall be defined as described in <a href=
"../../basedefs/sys/types.h.html"><i>&lt;sys/types.h&gt;</i></a>.</p>
<p>The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.</p>
<pre>
<tt>ssize_t readv(int, const struct iovec *, int);
ssize_t writev(int, const struct iovec *, int);
</tt>
</pre>
</blockquote>
<hr>
<div class="box"><em>The following sections are informative.</em></div>
<h4><a name="tag_13_68_04"></a>APPLICATION USAGE</h4>
<blockquote>
<p>The implementation can put a limit on the number of scatter/gather elements which can be processed in one call. The symbol
{IOV_MAX} defined in <a href="../../basedefs/limits.h.html"><i>&lt;limits.h&gt;</i></a> should always be used to learn about the
limits instead of assuming a fixed value.</p>
</blockquote>
<h4><a name="tag_13_68_05"></a>RATIONALE</h4>
<blockquote>
<p>Traditionally, the maximum number of scatter/gather elements the system can process in one call were described by the symbolic
value {UIO_MAXIOV}. In IEEE&nbsp;Std&nbsp;1003.1-2001 this value is replaced by the constant {IOV_MAX} which can be found in <a
href="../../basedefs/limits.h.html"><i>&lt;limits.h&gt;</i></a>.</p>
</blockquote>
<h4><a name="tag_13_68_06"></a>FUTURE DIRECTIONS</h4>
<blockquote>
<p>None.</p>
</blockquote>
<h4><a name="tag_13_68_07"></a>SEE ALSO</h4>
<blockquote>
<p><a href="../limits.h.html#tag_13_24"><i>&lt;limits.h&gt;</i></a> , <a href=
"../sys/types.h.html#tag_13_67"><i>&lt;sys/types.h&gt;</i></a> , the System Interfaces volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a
href="../../functions/read.html"><i>read</i>()</a>, <a href="../../functions/write.html"><i>write</i>()</a></p>
</blockquote>
<h4><a name="tag_13_68_08"></a>CHANGE HISTORY</h4>
<blockquote>
<p>First released in Issue 4, Version 2.</p>
</blockquote>
<h4><a name="tag_13_68_09"></a>Issue 6</h4>
<blockquote>
<p>Text referring to scatter/gather I/O is added to the DESCRIPTION.</p>
</blockquote>
<div class="box"><em>End of informative text.</em></div>
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