1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>write_at (3 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="../write_at.html" title="write_at"> 9<link rel="prev" href="overload2.html" title="write_at (2 of 8 overloads)"> 10<link rel="next" href="overload4.html" title="write_at (4 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="overload2.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../write_at.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.write_at.overload3"></a><a class="link" href="overload3.html" title="write_at (3 of 8 overloads)">write_at (3 28 of 8 overloads)</a> 29</h4></div></div></div> 30<p> 31 Write a certain amount of data at a specified offset before returning. 32 </p> 33<pre class="programlisting">template< 34 typename <a class="link" href="../SyncRandomAccessWriteDevice.html" title="Buffer-oriented synchronous random-access write device requirements">SyncRandomAccessWriteDevice</a>, 35 typename <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a>, 36 typename <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a>> 37std::size_t write_at( 38 SyncRandomAccessWriteDevice & d, 39 uint64_t offset, 40 const ConstBufferSequence & buffers, 41 CompletionCondition completion_condition); 42</pre> 43<p> 44 This function is used to write a certain number of bytes of data to a random 45 access device at a specified offset. The call will block until one of the 46 following conditions is true: 47 </p> 48<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 49<li class="listitem"> 50 All of the data in the supplied buffers has been written. That is, 51 the bytes transferred is equal to the sum of the buffer sizes. 52 </li> 53<li class="listitem"> 54 The completion_condition function object returns 0. 55 </li> 56</ul></div> 57<p> 58 This operation is implemented in terms of zero or more calls to the device's 59 write_some_at function. 60 </p> 61<h6> 62<a name="boost_asio.reference.write_at.overload3.h0"></a> 63 <span class="phrase"><a name="boost_asio.reference.write_at.overload3.parameters"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.parameters">Parameters</a> 64 </h6> 65<div class="variablelist"> 66<p class="title"><b></b></p> 67<dl class="variablelist"> 68<dt><span class="term">d</span></dt> 69<dd><p> 70 The device to which the data is to be written. The type must support 71 the SyncRandomAccessWriteDevice concept. 72 </p></dd> 73<dt><span class="term">offset</span></dt> 74<dd><p> 75 The offset at which the data will be written. 76 </p></dd> 77<dt><span class="term">buffers</span></dt> 78<dd><p> 79 One or more buffers containing the data to be written. The sum of 80 the buffer sizes indicates the maximum number of bytes to write to 81 the device. 82 </p></dd> 83<dt><span class="term">completion_condition</span></dt> 84<dd> 85<p> 86 The function object to be called to determine whether the write operation 87 is complete. The signature of the function object must be: 88</p> 89<pre class="programlisting">std::size_t completion_condition( 90 // Result of latest write_some_at operation. 91 const boost::system::error_code& error, 92 93 // Number of bytes transferred so far. 94 std::size_t bytes_transferred 95); 96</pre> 97<p> 98 A return value of 0 indicates that the write operation is complete. 99 A non-zero return value indicates the maximum number of bytes to 100 be written on the next call to the device's write_some_at function. 101 </p> 102</dd> 103</dl> 104</div> 105<h6> 106<a name="boost_asio.reference.write_at.overload3.h1"></a> 107 <span class="phrase"><a name="boost_asio.reference.write_at.overload3.return_value"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.return_value">Return Value</a> 108 </h6> 109<p> 110 The number of bytes transferred. 111 </p> 112<h6> 113<a name="boost_asio.reference.write_at.overload3.h2"></a> 114 <span class="phrase"><a name="boost_asio.reference.write_at.overload3.exceptions"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.exceptions">Exceptions</a> 115 </h6> 116<div class="variablelist"> 117<p class="title"><b></b></p> 118<dl class="variablelist"> 119<dt><span class="term">boost::system::system_error</span></dt> 120<dd><p> 121 Thrown on failure. 122 </p></dd> 123</dl> 124</div> 125<h6> 126<a name="boost_asio.reference.write_at.overload3.h3"></a> 127 <span class="phrase"><a name="boost_asio.reference.write_at.overload3.example"></a></span><a class="link" href="overload3.html#boost_asio.reference.write_at.overload3.example">Example</a> 128 </h6> 129<p> 130 To write a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 131 function as follows: 132 </p> 133<pre class="programlisting">boost::asio::write_at(d, 42, boost::asio::buffer(data, size), 134 boost::asio::transfer_at_least(32)); 135</pre> 136<p> 137 See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a> 138 documentation for information on writing multiple buffers in one go, and 139 how to use it with arrays, boost::array or std::vector. 140 </p> 141</div> 142<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 143<td align="left"></td> 144<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 145 Kohlhoff<p> 146 Distributed under the Boost Software License, Version 1.0. (See accompanying 147 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>) 148 </p> 149</div></td> 150</tr></table> 151<hr> 152<div class="spirit-nav"> 153<a accesskey="p" href="overload2.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../write_at.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> 154</div> 155</body> 156</html> 157
