1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>read (12 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="overload11.html" title="read (11 of 16 overloads)"> 10<link rel="next" href="overload13.html" title="read (13 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="overload11.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="overload13.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.overload12"></a><a class="link" href="overload12.html" title="read (12 of 16 overloads)">read (12 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 Allocator, 36 typename <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a>> 37std::size_t read( 38 SyncReadStream & s, 39 basic_streambuf< Allocator > & b, 40 CompletionCondition completion_condition, 41 boost::system::error_code & ec); 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 buffer is full (that is, it has reached maximum size). 50 </li> 51<li class="listitem"> 52 The completion_condition function object returns 0. 53 </li> 54</ul></div> 55<p> 56 This operation is implemented in terms of zero or more calls to the stream's 57 read_some function. 58 </p> 59<h6> 60<a name="boost_asio.reference.read.overload12.h0"></a> 61 <span class="phrase"><a name="boost_asio.reference.read.overload12.parameters"></a></span><a class="link" href="overload12.html#boost_asio.reference.read.overload12.parameters">Parameters</a> 62 </h6> 63<div class="variablelist"> 64<p class="title"><b></b></p> 65<dl class="variablelist"> 66<dt><span class="term">s</span></dt> 67<dd><p> 68 The stream from which the data is to be read. The type must support 69 the SyncReadStream concept. 70 </p></dd> 71<dt><span class="term">b</span></dt> 72<dd><p> 73 The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a> 74 object into which the data will be read. 75 </p></dd> 76<dt><span class="term">completion_condition</span></dt> 77<dd> 78<p> 79 The function object to be called to determine whether the read operation 80 is complete. The signature of the function object must be: 81</p> 82<pre class="programlisting">std::size_t completion_condition( 83 // Result of latest read_some operation. 84 const boost::system::error_code& error, 85 86 // Number of bytes transferred so far. 87 std::size_t bytes_transferred 88); 89</pre> 90<p> 91 A return value of 0 indicates that the read operation is complete. 92 A non-zero return value indicates the maximum number of bytes to 93 be read on the next call to the stream's read_some function. 94 </p> 95</dd> 96<dt><span class="term">ec</span></dt> 97<dd><p> 98 Set to indicate what error occurred, if any. 99 </p></dd> 100</dl> 101</div> 102<h6> 103<a name="boost_asio.reference.read.overload12.h1"></a> 104 <span class="phrase"><a name="boost_asio.reference.read.overload12.return_value"></a></span><a class="link" href="overload12.html#boost_asio.reference.read.overload12.return_value">Return 105 Value</a> 106 </h6> 107<p> 108 The number of bytes read. If an error occurs, returns the total number 109 of bytes successfully transferred prior to the error. 110 </p> 111</div> 112<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 113<td align="left"></td> 114<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 115 Kohlhoff<p> 116 Distributed under the Boost Software License, Version 1.0. (See accompanying 117 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>) 118 </p> 119</div></td> 120</tr></table> 121<hr> 122<div class="spirit-nav"> 123<a accesskey="p" href="overload11.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="overload13.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 124</div> 125</body> 126</html> 127
