1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>async_write (2 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_write.html" title="async_write"> 9<link rel="prev" href="overload1.html" title="async_write (1 of 8 overloads)"> 10<link rel="next" href="overload3.html" title="async_write (3 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="overload1.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_write.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="overload3.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_write.overload2"></a><a class="link" href="overload2.html" title="async_write (2 of 8 overloads)">async_write 28 (2 of 8 overloads)</a> 29</h4></div></div></div> 30<p> 31 Start an asynchronous operation to write a certain amount of data to a 32 stream. 33 </p> 34<pre class="programlisting">template< 35 typename <a class="link" href="../AsyncWriteStream.html" title="Buffer-oriented asynchronous write stream requirements">AsyncWriteStream</a>, 36 typename <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a>, 37 typename <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a>, 38 typename <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a>> 39<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_write( 40 AsyncWriteStream & s, 41 const ConstBufferSequence & buffers, 42 CompletionCondition completion_condition, 43 WriteHandler && handler, 44 typename enable_if< is_const_buffer_sequence< ConstBufferSequence >::value >::type * = 0); 45</pre> 46<p> 47 This function is used to asynchronously write a certain number of bytes 48 of data to a stream. The function call always returns immediately. The 49 asynchronous operation will continue until one of the following conditions 50 is true: 51 </p> 52<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 53<li class="listitem"> 54 All of the data in the supplied buffers has been written. That is, 55 the bytes transferred is equal to the sum of the buffer sizes. 56 </li> 57<li class="listitem"> 58 The completion_condition function object returns 0. 59 </li> 60</ul></div> 61<p> 62 This operation is implemented in terms of zero or more calls to the stream's 63 async_write_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>. 64 The program must ensure that the stream performs no other write operations 65 (such as async_write, the stream's async_write_some function, or any other 66 composed operations that perform writes) until this operation completes. 67 </p> 68<h6> 69<a name="boost_asio.reference.async_write.overload2.h0"></a> 70 <span class="phrase"><a name="boost_asio.reference.async_write.overload2.parameters"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.parameters">Parameters</a> 71 </h6> 72<div class="variablelist"> 73<p class="title"><b></b></p> 74<dl class="variablelist"> 75<dt><span class="term">s</span></dt> 76<dd><p> 77 The stream to which the data is to be written. The type must support 78 the AsyncWriteStream concept. 79 </p></dd> 80<dt><span class="term">buffers</span></dt> 81<dd><p> 82 One or more buffers containing the data to be written. Although the 83 buffers object may be copied as necessary, ownership of the underlying 84 memory blocks is retained by the caller, which must guarantee that 85 they remain valid until the handler is called. 86 </p></dd> 87<dt><span class="term">completion_condition</span></dt> 88<dd> 89<p> 90 The function object to be called to determine whether the write operation 91 is complete. The signature of the function object must be: 92</p> 93<pre class="programlisting">std::size_t completion_condition( 94 // Result of latest async_write_some operation. 95 const boost::system::error_code& error, 96 97 // Number of bytes transferred so far. 98 std::size_t bytes_transferred 99); 100</pre> 101<p> 102 A return value of 0 indicates that the write operation is complete. 103 A non-zero return value indicates the maximum number of bytes to 104 be written on the next call to the stream's async_write_some function. 105 </p> 106</dd> 107<dt><span class="term">handler</span></dt> 108<dd> 109<p> 110 The handler to be called when the write operation completes. Copies 111 will be made of the handler as required. The function signature of 112 the handler must be: 113</p> 114<pre class="programlisting">void handler( 115 const boost::system::error_code& error, // Result of operation. 116 117 std::size_t bytes_transferred // Number of bytes written from the 118 // buffers. If an error occurred, 119 // this will be less than the sum 120 // of the buffer sizes. 121); 122</pre> 123<p> 124 Regardless of whether the asynchronous operation completes immediately 125 or not, the handler will not be invoked from within this function. 126 On immediate completion, invocation of the handler will be performed 127 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>. 128 </p> 129</dd> 130</dl> 131</div> 132<h6> 133<a name="boost_asio.reference.async_write.overload2.h1"></a> 134 <span class="phrase"><a name="boost_asio.reference.async_write.overload2.example"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.example">Example</a> 135 </h6> 136<p> 137 To write a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 138 function as follows: 139 </p> 140<pre class="programlisting">boost::asio::async_write(s, 141 boost::asio::buffer(data, size), 142 boost::asio::transfer_at_least(32), 143 handler); 144</pre> 145<p> 146 See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 147 documentation for information on writing multiple buffers in one go, and 148 how to use it with arrays, boost::array or std::vector. 149 </p> 150</div> 151<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 152<td align="left"></td> 153<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 154 Kohlhoff<p> 155 Distributed under the Boost Software License, Version 1.0. (See accompanying 156 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>) 157 </p> 158</div></td> 159</tr></table> 160<hr> 161<div class="spirit-nav"> 162<a accesskey="p" href="overload1.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_write.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="overload3.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 163</div> 164</body> 165</html> 166
