1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read_at (1 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="../read_at.html" title="read_at"> 10<link rel="next" href="overload2.html" title="read_at (2 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="../read_at.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="overload2.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.overload1"></a><a class="link" href="overload1.html" title="read_at (1 of 8 overloads)">read_at (1 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 <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a>> 37std::size_t read_at( 38 SyncRandomAccessReadDevice & d, 39 uint64_t offset, 40 const MutableBufferSequence & buffers); 41</pre> 42<p> 43 This function is used to read a certain number of bytes of data from a 44 random access device at the specified offset. The call will block until 45 one of the following conditions is true: 46 </p> 47<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 48<li class="listitem"> 49 The supplied buffers are full. That is, the bytes transferred is equal 50 to the sum of the buffer sizes. 51 </li> 52<li class="listitem"> 53 An error occurred. 54 </li> 55</ul></div> 56<p> 57 This operation is implemented in terms of zero or more calls to the device's 58 read_some_at function. 59 </p> 60<h6> 61<a name="boost_asio.reference.read_at.overload1.h0"></a> 62 <span class="phrase"><a name="boost_asio.reference.read_at.overload1.parameters"></a></span><a class="link" href="overload1.html#boost_asio.reference.read_at.overload1.parameters">Parameters</a> 63 </h6> 64<div class="variablelist"> 65<p class="title"><b></b></p> 66<dl class="variablelist"> 67<dt><span class="term">d</span></dt> 68<dd><p> 69 The device from which the data is to be read. The type must support 70 the SyncRandomAccessReadDevice concept. 71 </p></dd> 72<dt><span class="term">offset</span></dt> 73<dd><p> 74 The offset at which the data will be read. 75 </p></dd> 76<dt><span class="term">buffers</span></dt> 77<dd><p> 78 One or more buffers into which the data will be read. The sum of 79 the buffer sizes indicates the maximum number of bytes to read from 80 the device. 81 </p></dd> 82</dl> 83</div> 84<h6> 85<a name="boost_asio.reference.read_at.overload1.h1"></a> 86 <span class="phrase"><a name="boost_asio.reference.read_at.overload1.return_value"></a></span><a class="link" href="overload1.html#boost_asio.reference.read_at.overload1.return_value">Return Value</a> 87 </h6> 88<p> 89 The number of bytes transferred. 90 </p> 91<h6> 92<a name="boost_asio.reference.read_at.overload1.h2"></a> 93 <span class="phrase"><a name="boost_asio.reference.read_at.overload1.exceptions"></a></span><a class="link" href="overload1.html#boost_asio.reference.read_at.overload1.exceptions">Exceptions</a> 94 </h6> 95<div class="variablelist"> 96<p class="title"><b></b></p> 97<dl class="variablelist"> 98<dt><span class="term">boost::system::system_error</span></dt> 99<dd><p> 100 Thrown on failure. 101 </p></dd> 102</dl> 103</div> 104<h6> 105<a name="boost_asio.reference.read_at.overload1.h3"></a> 106 <span class="phrase"><a name="boost_asio.reference.read_at.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.read_at.overload1.example">Example</a> 107 </h6> 108<p> 109 To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 110 function as follows: 111 </p> 112<pre class="programlisting">boost::asio::read_at(d, 42, boost::asio::buffer(data, size)); 113</pre> 114<p> 115 See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 116 documentation for information on reading into multiple buffers in one go, 117 and how to use it with arrays, boost::array or std::vector. 118 </p> 119<h6> 120<a name="boost_asio.reference.read_at.overload1.h4"></a> 121 <span class="phrase"><a name="boost_asio.reference.read_at.overload1.remarks"></a></span><a class="link" href="overload1.html#boost_asio.reference.read_at.overload1.remarks">Remarks</a> 122 </h6> 123<p> 124 This overload is equivalent to calling: 125 </p> 126<pre class="programlisting">boost::asio::read_at( 127 d, 42, buffers, 128 boost::asio::transfer_all()); 129</pre> 130</div> 131<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 132<td align="left"></td> 133<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 134 Kohlhoff<p> 135 Distributed under the Boost Software License, Version 1.0. (See accompanying 136 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>) 137 </p> 138</div></td> 139</tr></table> 140<hr> 141<div class="spirit-nav"> 142<a accesskey="p" href="../read_at.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="overload2.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 143</div> 144</body> 145</html> 146
