1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>async_read (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="../async_read.html" title="async_read"> 9<link rel="prev" href="../async_read.html" title="async_read"> 10<link rel="next" href="overload2.html" title="async_read (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="../async_read.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="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.async_read.overload1"></a><a class="link" href="overload1.html" title="async_read (1 of 8 overloads)">async_read 28 (1 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="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</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 const MutableBufferSequence & 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_mutable_buffer_sequence< MutableBufferSequence >::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 supplied buffers are full. That is, the bytes transferred is equal 53 to the sum of the buffer sizes. 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.overload1.h0"></a> 68 <span class="phrase"><a name="boost_asio.reference.async_read.overload1.parameters"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.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 One or more buffers into which the data will be read. The sum of 81 the buffer sizes indicates the maximum number of bytes to read from 82 the stream. Although the buffers object may be copied as necessary, 83 ownership of the underlying memory blocks is retained by the caller, 84 which must guarantee that they remain valid until the handler is 85 called. 86 </p></dd> 87<dt><span class="term">handler</span></dt> 88<dd> 89<p> 90 The handler to be called when the read operation completes. Copies 91 will be made of the handler as required. The function signature of 92 the handler must be: 93</p> 94<pre class="programlisting">void handler( 95 const boost::system::error_code& error, // Result of operation. 96 97 std::size_t bytes_transferred // Number of bytes copied into the 98 // buffers. If an error occurred, 99 // this will be the number of 100 // bytes successfully transferred 101 // prior to the error. 102); 103</pre> 104<p> 105 Regardless of whether the asynchronous operation completes immediately 106 or not, the handler will not be invoked from within this function. 107 On immediate completion, invocation of the handler will be performed 108 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>. 109 </p> 110</dd> 111</dl> 112</div> 113<h6> 114<a name="boost_asio.reference.async_read.overload1.h1"></a> 115 <span class="phrase"><a name="boost_asio.reference.async_read.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.example">Example</a> 116 </h6> 117<p> 118 To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 119 function as follows: 120 </p> 121<pre class="programlisting">boost::asio::async_read(s, boost::asio::buffer(data, size), handler); 122</pre> 123<p> 124 See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 125 documentation for information on reading into multiple buffers in one go, 126 and how to use it with arrays, boost::array or std::vector. 127 </p> 128<h6> 129<a name="boost_asio.reference.async_read.overload1.h2"></a> 130 <span class="phrase"><a name="boost_asio.reference.async_read.overload1.remarks"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_read.overload1.remarks">Remarks</a> 131 </h6> 132<p> 133 This overload is equivalent to calling: 134 </p> 135<pre class="programlisting">boost::asio::async_read( 136 s, buffers, 137 boost::asio::transfer_all(), 138 handler); 139</pre> 140</div> 141<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 142<td align="left"></td> 143<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 144 Kohlhoff<p> 145 Distributed under the Boost Software License, Version 1.0. (See accompanying 146 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>) 147 </p> 148</div></td> 149</tr></table> 150<hr> 151<div class="spirit-nav"> 152<a accesskey="p" href="../async_read.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="overload2.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 153</div> 154</body> 155</html> 156
