1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read (3 of 16 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.html" title="read"> 9<link rel="prev" href="overload2.html" title="read (2 of 16 overloads)"> 10<link rel="next" href="overload4.html" title="read (4 of 16 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="../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.read.overload3"></a><a class="link" href="overload3.html" title="read (3 of 16 overloads)">read (3 of 16 28 overloads)</a> 29</h4></div></div></div> 30<p> 31 Attempt to read a certain amount of data from a stream before returning. 32 </p> 33<pre class="programlisting">template< 34 typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>, 35 typename <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a>, 36 typename <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a>> 37std::size_t read( 38 SyncReadStream & s, 39 const MutableBufferSequence & buffers, 40 CompletionCondition completion_condition, 41 typename enable_if< is_mutable_buffer_sequence< MutableBufferSequence >::value >::type * = 0); 42</pre> 43<p> 44 This function is used to read a certain number of bytes of data from a 45 stream. The call will block until 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 The completion_condition function object returns 0. 54 </li> 55</ul></div> 56<p> 57 This operation is implemented in terms of zero or more calls to the stream's 58 read_some function. 59 </p> 60<h6> 61<a name="boost_asio.reference.read.overload3.h0"></a> 62 <span class="phrase"><a name="boost_asio.reference.read.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.read.overload3.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">s</span></dt> 68<dd><p> 69 The stream from which the data is to be read. The type must support 70 the SyncReadStream concept. 71 </p></dd> 72<dt><span class="term">buffers</span></dt> 73<dd><p> 74 One or more buffers into which the data will be read. The sum of 75 the buffer sizes indicates the maximum number of bytes to read from 76 the stream. 77 </p></dd> 78<dt><span class="term">completion_condition</span></dt> 79<dd> 80<p> 81 The function object to be called to determine whether the read operation 82 is complete. The signature of the function object must be: 83</p> 84<pre class="programlisting">std::size_t completion_condition( 85 // Result of latest read_some operation. 86 const boost::system::error_code& error, 87 88 // Number of bytes transferred so far. 89 std::size_t bytes_transferred 90); 91</pre> 92<p> 93 A return value of 0 indicates that the read operation is complete. 94 A non-zero return value indicates the maximum number of bytes to 95 be read on the next call to the stream's read_some function. 96 </p> 97</dd> 98</dl> 99</div> 100<h6> 101<a name="boost_asio.reference.read.overload3.h1"></a> 102 <span class="phrase"><a name="boost_asio.reference.read.overload3.return_value"></a></span><a class="link" href="overload3.html#boost_asio.reference.read.overload3.return_value">Return 103 Value</a> 104 </h6> 105<p> 106 The number of bytes transferred. 107 </p> 108<h6> 109<a name="boost_asio.reference.read.overload3.h2"></a> 110 <span class="phrase"><a name="boost_asio.reference.read.overload3.exceptions"></a></span><a class="link" href="overload3.html#boost_asio.reference.read.overload3.exceptions">Exceptions</a> 111 </h6> 112<div class="variablelist"> 113<p class="title"><b></b></p> 114<dl class="variablelist"> 115<dt><span class="term">boost::system::system_error</span></dt> 116<dd><p> 117 Thrown on failure. 118 </p></dd> 119</dl> 120</div> 121<h6> 122<a name="boost_asio.reference.read.overload3.h3"></a> 123 <span class="phrase"><a name="boost_asio.reference.read.overload3.example"></a></span><a class="link" href="overload3.html#boost_asio.reference.read.overload3.example">Example</a> 124 </h6> 125<p> 126 To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 127 function as follows: 128 </p> 129<pre class="programlisting">boost::asio::read(s, boost::asio::buffer(data, size), 130 boost::asio::transfer_at_least(32)); 131</pre> 132<p> 133 See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 134 documentation for information on reading into multiple buffers in one go, 135 and how to use it with arrays, boost::array or std::vector. 136 </p> 137</div> 138<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 139<td align="left"></td> 140<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 141 Kohlhoff<p> 142 Distributed under the Boost Software License, Version 1.0. (See accompanying 143 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>) 144 </p> 145</div></td> 146</tr></table> 147<hr> 148<div class="spirit-nav"> 149<a accesskey="p" href="overload2.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../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> 150</div> 151</body> 152</html> 153
