<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>read_at (3 of 6 overloads)</title>
<link rel="stylesheet" href="../../../boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2">
<link rel="start" href="../../../index.html" title="Asio">
<link rel="up" href="../read_at.html" title="read_at">
<link rel="prev" href="overload2.html" title="read_at (2 of 6 overloads)">
<link rel="next" href="overload4.html" title="read_at (4 of 6 overloads)">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="overload2.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload4.html"><img src="../../../next.png" alt="Next"></a>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.read_at.overload3"></a><a class="link" href="overload3.html" title="read_at (3 of 6 overloads)">read_at (3 of 6 overloads)</a>
</h4></div></div></div>
<p>
Attempt to read a certain amount of data at the specified offset before
returning.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">SyncRandomAccessReadDevice</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">></span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read_at</span><span class="special">(</span>
<span class="identifier">SyncRandomAccessReadDevice</span> <span class="special">&</span> <span class="identifier">d</span><span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span class="special">&</span> <span class="identifier">buffers</span><span class="special">,</span>
<span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
This function is used to read a certain number of bytes of data from a
random access device at the specified offset. The call will block until
one of the following conditions is true:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
The supplied buffers are full. That is, the bytes transferred is equal
to the sum of the buffer sizes.
</li>
<li>
The completion_condition function object returns 0.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the device's
read_some_at function.
</p>
<a name="asio.reference.read_at.overload3.parameters"></a><h6>
<a name="id1114304"></a>
<a class="link" href="overload3.html#asio.reference.read_at.overload3.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">d</span></dt>
<dd><p>
The device from which the data is to be read. The type must support
the SyncRandomAccessReadDevice concept.
</p></dd>
<dt><span class="term">offset</span></dt>
<dd><p>
The offset at which the data will be read.
</p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
One or more buffers into which the data will be read. The sum of
the buffer sizes indicates the maximum number of bytes to read from
the device.
</p></dd>
<dt><span class="term">completion_condition</span></dt>
<dd>
<p>
The function object to be called to determine whether the read operation
is complete. The signature of the function object must be:
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">completion_condition</span><span class="special">(</span>
<span class="comment">// Result of latest read_some_at operation.
</span> <span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span>
<span class="comment">// Number of bytes transferred so far.
</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
<p>
A return value of 0 indicates that the read operation is complete.
A non-zero return value indicates the maximum number of bytes to
be read on the next call to the device's read_some_at function.
</p>
</dd>
<dt><span class="term">ec</span></dt>
<dd><p>
Set to indicate what error occurred, if any.
</p></dd>
</dl>
</div>
<a name="asio.reference.read_at.overload3.return_value"></a><h6>
<a name="id1114506"></a>
<a class="link" href="overload3.html#asio.reference.read_at.overload3.return_value">Return Value</a>
</h6>
<p>
The number of bytes read. If an error occurs, returns the total number
of bytes successfully transferred prior to the error.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="overload2.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload4.html"><img src="../../../next.png" alt="Next"></a>
</div>
</body>
</html>
distrib
>
Mageia
>
5
>
i586
>
media
>
core-release
>
by-pkgid
>
3ff61ef50f7b6da9fdee54352ae073f9
>
files
>
2203
