1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read_at (6 of 8 overloads)</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../read_at.html" title="read_at"> 9<link rel="prev" href="overload5.html" title="read_at (5 of 8 overloads)"> 10<link rel="next" href="overload7.html" title="read_at (7 of 8 overloads)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="overload5.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload7.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="boost_asio.reference.read_at.overload6"></a><a class="link" href="overload6.html" title="read_at (6 of 8 overloads)">read_at (6 28 of 8 overloads)</a> 29</h4></div></div></div> 30<p> 31 Attempt to read a certain amount of data at the specified offset before 32 returning. 33 </p> 34<pre class="programlisting">template< 35 typename <a class="link" href="../SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">SyncRandomAccessReadDevice</a>, 36 typename Allocator> 37std::size_t read_at( 38 SyncRandomAccessReadDevice & d, 39 uint64_t offset, 40 basic_streambuf< Allocator > & b, 41 boost::system::error_code & ec); 42</pre> 43<p> 44 This function is used to read a certain number of bytes of data from a 45 random access device at the specified offset. The call will block until 46 one of the following conditions is true: 47 </p> 48<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 49 An error occurred. 50 </li></ul></div> 51<p> 52 This operation is implemented in terms of zero or more calls to the device's 53 read_some_at function. 54 </p> 55<h6> 56<a name="boost_asio.reference.read_at.overload6.h0"></a> 57 <span class="phrase"><a name="boost_asio.reference.read_at.overload6.parameters"></a></span><a class="link" href="overload6.html#boost_asio.reference.read_at.overload6.parameters">Parameters</a> 58 </h6> 59<div class="variablelist"> 60<p class="title"><b></b></p> 61<dl class="variablelist"> 62<dt><span class="term">d</span></dt> 63<dd><p> 64 The device from which the data is to be read. The type must support 65 the SyncRandomAccessReadDevice concept. 66 </p></dd> 67<dt><span class="term">offset</span></dt> 68<dd><p> 69 The offset at which the data will be read. 70 </p></dd> 71<dt><span class="term">b</span></dt> 72<dd><p> 73 The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a> 74 object into which the data will be read. 75 </p></dd> 76<dt><span class="term">ec</span></dt> 77<dd><p> 78 Set to indicate what error occurred, if any. 79 </p></dd> 80</dl> 81</div> 82<h6> 83<a name="boost_asio.reference.read_at.overload6.h1"></a> 84 <span class="phrase"><a name="boost_asio.reference.read_at.overload6.return_value"></a></span><a class="link" href="overload6.html#boost_asio.reference.read_at.overload6.return_value">Return Value</a> 85 </h6> 86<p> 87 The number of bytes transferred. 88 </p> 89<h6> 90<a name="boost_asio.reference.read_at.overload6.h2"></a> 91 <span class="phrase"><a name="boost_asio.reference.read_at.overload6.remarks"></a></span><a class="link" href="overload6.html#boost_asio.reference.read_at.overload6.remarks">Remarks</a> 92 </h6> 93<p> 94 This overload is equivalent to calling: 95 </p> 96<pre class="programlisting">boost::asio::read_at( 97 d, 42, b, 98 boost::asio::transfer_all(), ec); 99</pre> 100</div> 101<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 102<td align="left"></td> 103<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 104 Kohlhoff<p> 105 Distributed under the Boost Software License, Version 1.0. (See accompanying 106 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>) 107 </p> 108</div></td> 109</tr></table> 110<hr> 111<div class="spirit-nav"> 112<a accesskey="p" href="overload5.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload7.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 113</div> 114</body> 115</html> 116
