1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>async_read (5 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="overload4.html" title="async_read (4 of 8 overloads)"> 10<link rel="next" href="overload6.html" title="async_read (6 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="overload4.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="overload6.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.overload5"></a><a class="link" href="overload5.html" title="async_read (5 of 8 overloads)">async_read 28 (5 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 Allocator, 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 basic_streambuf< Allocator > & b, 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</pre> 43<p> 44 This function is used to asynchronously read a certain number of bytes 45 of data from a stream. The function call always returns immediately. The 46 asynchronous operation will continue until one of the following conditions 47 is true: 48 </p> 49<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 50<li class="listitem"> 51 The supplied buffer is full (that is, it has reached maximum size). 52 </li> 53<li class="listitem"> 54 An error occurred. 55 </li> 56</ul></div> 57<p> 58 This operation is implemented in terms of zero or more calls to the stream's 59 async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>. 60 The program must ensure that the stream performs no other read operations 61 (such as async_read, the stream's async_read_some function, or any other 62 composed operations that perform reads) until this operation completes. 63 </p> 64<h6> 65<a name="boost_asio.reference.async_read.overload5.h0"></a> 66 <span class="phrase"><a name="boost_asio.reference.async_read.overload5.parameters"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read.overload5.parameters">Parameters</a> 67 </h6> 68<div class="variablelist"> 69<p class="title"><b></b></p> 70<dl class="variablelist"> 71<dt><span class="term">s</span></dt> 72<dd><p> 73 The stream from which the data is to be read. The type must support 74 the AsyncReadStream concept. 75 </p></dd> 76<dt><span class="term">b</span></dt> 77<dd><p> 78 A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a> 79 object into which the data will be read. Ownership of the streambuf 80 is retained by the caller, which must guarantee that it remains valid 81 until the handler is called. 82 </p></dd> 83<dt><span class="term">handler</span></dt> 84<dd> 85<p> 86 The handler to be called when the read operation completes. Copies 87 will be made of the handler as required. The function signature of 88 the handler must be: 89</p> 90<pre class="programlisting">void handler( 91 const boost::system::error_code& error, // Result of operation. 92 93 std::size_t bytes_transferred // Number of bytes copied into the 94 // buffers. If an error occurred, 95 // this will be the number of 96 // bytes successfully transferred 97 // prior to the error. 98); 99</pre> 100<p> 101 Regardless of whether the asynchronous operation completes immediately 102 or not, the handler will not be invoked from within this function. 103 On immediate completion, invocation of the handler will be performed 104 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>. 105 </p> 106</dd> 107</dl> 108</div> 109<h6> 110<a name="boost_asio.reference.async_read.overload5.h1"></a> 111 <span class="phrase"><a name="boost_asio.reference.async_read.overload5.remarks"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read.overload5.remarks">Remarks</a> 112 </h6> 113<p> 114 This overload is equivalent to calling: 115 </p> 116<pre class="programlisting">boost::asio::async_read( 117 s, b, 118 boost::asio::transfer_all(), 119 handler); 120</pre> 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="overload4.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="overload6.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 134</div> 135</body> 136</html> 137
