1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Buffer-oriented asynchronous random-access read device requirements</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="../reference.html" title="Reference"> 9<link rel="prev" href="AcceptHandler.html" title="Accept handler requirements"> 10<link rel="next" href="AsyncRandomAccessWriteDevice.html" title="Buffer-oriented asynchronous random-access write device requirements"> 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="AcceptHandler.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="AsyncRandomAccessWriteDevice.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.reference.AsyncRandomAccessReadDevice"></a><a class="link" href="AsyncRandomAccessReadDevice.html" title="Buffer-oriented asynchronous random-access read device requirements">Buffer-oriented 28 asynchronous random-access read device requirements</a> 29</h3></div></div></div> 30<p> 31 In the table below, <code class="computeroutput">a</code> denotes an asynchronous random access 32 read device object, <code class="computeroutput">o</code> denotes an offset of type <code class="computeroutput">boost::uint64_t</code>, 33 <code class="computeroutput">mb</code> denotes an object satisfying <a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable 34 buffer sequence</a> requirements, and <code class="computeroutput">h</code> denotes an object 35 satisfying <a class="link" href="ReadHandler.html" title="Read handler requirements">read handler</a> 36 requirements. 37 </p> 38<div class="table"> 39<a name="boost_asio.reference.AsyncRandomAccessReadDevice.t0"></a><p class="title"><b>Table 2. Buffer-oriented asynchronous random-access read device requirements</b></p> 40<div class="table-contents"><table class="table" summary="Buffer-oriented asynchronous random-access read device requirements"> 41<colgroup> 42<col> 43<col> 44<col> 45</colgroup> 46<thead><tr> 47<th> 48 <p> 49 operation 50 </p> 51 </th> 52<th> 53 <p> 54 type 55 </p> 56 </th> 57<th> 58 <p> 59 semantics, pre/post-conditions 60 </p> 61 </th> 62</tr></thead> 63<tbody> 64<tr> 65<td> 66 <p> 67 <code class="computeroutput">a.get_executor()</code> 68 </p> 69 </td> 70<td> 71 <p> 72 A type satisfying the <a class="link" href="Executor1.html" title="Executor requirements">Executor 73 requirements</a>. 74 </p> 75 </td> 76<td> 77 <p> 78 Returns the associated I/O executor. 79 </p> 80 </td> 81</tr> 82<tr> 83<td> 84 <p> 85 <code class="computeroutput">a.async_read_some_at(o, mb, h);</code> 86 </p> 87 </td> 88<td> 89 <p> 90 <code class="computeroutput">void</code> 91 </p> 92 </td> 93<td> 94 <p> 95 Initiates an asynchronous operation to read one or more bytes of 96 data from the device <code class="computeroutput">a</code> at the offset <code class="computeroutput">o</code>. 97 The operation is performed via the <code class="computeroutput">io_service</code> object 98 <code class="computeroutput">a.get_io_service()</code> and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous 99 operation</a> requirements.<br> <br> The mutable buffer 100 sequence <code class="computeroutput">mb</code> specifies memory where the data should 101 be placed. The <code class="computeroutput">async_read_some_at</code> operation shall 102 always fill a buffer in the sequence completely before proceeding 103 to the next.<br> <br> The implementation shall maintain one 104 or more copies of <code class="computeroutput">mb</code> until such time as the read operation 105 no longer requires access to the memory specified by the buffers 106 in the sequence. The program must ensure the memory is valid until:<br> 107 <br> — the last copy of <code class="computeroutput">mb</code> is destroyed, or<br> 108 <br> — the handler for the asynchronous read operation is invoked,<br> 109 <br> whichever comes first.<br> <br> If the total size of 110 all buffers in the sequence <code class="computeroutput">mb</code> is <code class="computeroutput">0</code>, 111 the asynchronous read operation shall complete immediately and 112 pass <code class="computeroutput">0</code> as the argument to the handler that specifies 113 the number of bytes read. 114 </p> 115 </td> 116</tr> 117</tbody> 118</table></div> 119</div> 120<br class="table-break"> 121</div> 122<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 123<td align="left"></td> 124<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 125 Kohlhoff<p> 126 Distributed under the Boost Software License, Version 1.0. (See accompanying 127 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>) 128 </p> 129</div></td> 130</tr></table> 131<hr> 132<div class="spirit-nav"> 133<a accesskey="p" href="AcceptHandler.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="AsyncRandomAccessWriteDevice.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 134</div> 135</body> 136</html> 137
