1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>async_read (3 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="../async_read.html" title="async_read"> 9<link rel="prev" href="overload2.html" title="async_read (2 of 8 overloads)"> 10<link rel="next" href="overload4.html" title="async_read (4 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="overload2.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_read.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="overload4.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.async_read.overload3"></a><a class="link" href="overload3.html" title="async_read (3 of 8 overloads)">async_read 28 (3 of 8 overloads)</a> 29</h4></div></div></div> 30<p> 31 Start an asynchronous operation to read a certain amount of data from a 32 stream. 33 </p> 34<pre class="programlisting">template< 35 typename <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a>, 36 typename <a class="link" href="../DynamicBuffer_v1.html" title="Dynamic buffer requirements (version 1)">DynamicBuffer_v1</a>, 37 typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a> = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>> 38<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_read( 39 AsyncReadStream & s, 40 DynamicBuffer_v1 && buffers, 41 ReadHandler && handler = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>, 42 typename enable_if< is_dynamic_buffer_v1< typename decay< DynamicBuffer_v1 >::type >::value &&!is_dynamic_buffer_v2< typename decay< DynamicBuffer_v1 >::type >::value >::type * = 0); 43</pre> 44<p> 45 This function is used to asynchronously read a certain number of bytes 46 of data from a stream. The function call always returns immediately. The 47 asynchronous operation will continue until one of the following conditions 48 is true: 49 </p> 50<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 51<li class="listitem"> 52 The specified dynamic buffer sequence is full (that is, it has reached 53 maximum size). 54 </li> 55<li class="listitem"> 56 An error occurred. 57 </li> 58</ul></div> 59<p> 60 This operation is implemented in terms of zero or more calls to the stream's 61 async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>. 62 The program must ensure that the stream performs no other read operations 63 (such as async_read, the stream's async_read_some function, or any other 64 composed operations that perform reads) until this operation completes. 65 </p> 66<h6> 67<a name="boost_asio.reference.async_read.overload3.h0"></a> 68 <span class="phrase"><a name="boost_asio.reference.async_read.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_read.overload3.parameters">Parameters</a> 69 </h6> 70<div class="variablelist"> 71<p class="title"><b></b></p> 72<dl class="variablelist"> 73<dt><span class="term">s</span></dt> 74<dd><p> 75 The stream from which the data is to be read. The type must support 76 the AsyncReadStream concept. 77 </p></dd> 78<dt><span class="term">buffers</span></dt> 79<dd><p> 80 The dynamic buffer sequence into which the data will be read. Although 81 the buffers object may be copied as necessary, ownership of the underlying 82 memory blocks is retained by the caller, which must guarantee that 83 they remain valid until the handler is called. 84 </p></dd> 85<dt><span class="term">handler</span></dt> 86<dd> 87<p> 88 The handler to be called when the read operation completes. Copies 89 will be made of the handler as required. The function signature of 90 the handler must be: 91</p> 92<pre class="programlisting">void handler( 93 const boost::system::error_code& error, // Result of operation. 94 95 std::size_t bytes_transferred // Number of bytes copied into the 96 // buffers. If an error occurred, 97 // this will be the number of 98 // bytes successfully transferred 99 // prior to the error. 100); 101</pre> 102<p> 103 Regardless of whether the asynchronous operation completes immediately 104 or not, the handler will not be invoked from within this function. 105 On immediate completion, invocation of the handler will be performed 106 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>. 107 </p> 108</dd> 109</dl> 110</div> 111<h6> 112<a name="boost_asio.reference.async_read.overload3.h1"></a> 113 <span class="phrase"><a name="boost_asio.reference.async_read.overload3.remarks"></a></span><a class="link" href="overload3.html#boost_asio.reference.async_read.overload3.remarks">Remarks</a> 114 </h6> 115<p> 116 This overload is equivalent to calling: 117 </p> 118<pre class="programlisting">boost::asio::async_read( 119 s, buffers, 120 boost::asio::transfer_all(), 121 handler); 122</pre> 123</div> 124<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 125<td align="left"></td> 126<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 127 Kohlhoff<p> 128 Distributed under the Boost Software License, Version 1.0. (See accompanying 129 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>) 130 </p> 131</div></td> 132</tr></table> 133<hr> 134<div class="spirit-nav"> 135<a accesskey="p" href="overload2.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_read.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="overload4.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 136</div> 137</body> 138</html> 139
