<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>read_at (1 of 8 overloads)</title> <link rel="stylesheet" href="../../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../../index.html" title="Asio"> <link rel="up" href="../read_at.html" title="read_at"> <link rel="prev" href="../read_at.html" title="read_at"> <link rel="next" href="overload2.html" title="read_at (2 of 8 overloads)"> <meta name="viewport" content="width=device-width, initial-scale=1"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../read_at.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload2.html"><img src="../../../next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="asio.reference.read_at.overload1"></a><a class="link" href="overload1.html" title="read_at (1 of 8 overloads)">read_at (1 of 8 overloads)</a> </h4></div></div></div> <p> Attempt to read a certain amount of data at the specified offset before returning. </p> <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <a class="link" href="../SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">SyncRandomAccessReadDevice</a><span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a><span class="special">></span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read_at</span><span class="special">(</span> <span class="identifier">SyncRandomAccessReadDevice</span> <span class="special">&</span> <span class="identifier">d</span><span class="special">,</span> <span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span class="special">&</span> <span class="identifier">buffers</span><span class="special">);</span> </pre> <p> This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes. </li> <li class="listitem"> An error occurred. </li> </ul></div> <p> This operation is implemented in terms of zero or more calls to the device's read_some_at function. </p> <h6> <a name="asio.reference.read_at.overload1.h0"></a> <span><a name="asio.reference.read_at.overload1.parameters"></a></span><a class="link" href="overload1.html#asio.reference.read_at.overload1.parameters">Parameters</a> </h6> <div class="variablelist"> <p class="title"><b></b></p> <dl> <dt><span class="term">d</span></dt> <dd><p> The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept. </p></dd> <dt><span class="term">offset</span></dt> <dd><p> The offset at which the data will be read. </p></dd> <dt><span class="term">buffers</span></dt> <dd><p> One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the device. </p></dd> </dl> </div> <h6> <a name="asio.reference.read_at.overload1.h1"></a> <span><a name="asio.reference.read_at.overload1.return_value"></a></span><a class="link" href="overload1.html#asio.reference.read_at.overload1.return_value">Return Value</a> </h6> <p> The number of bytes transferred. </p> <h6> <a name="asio.reference.read_at.overload1.h2"></a> <span><a name="asio.reference.read_at.overload1.exceptions"></a></span><a class="link" href="overload1.html#asio.reference.read_at.overload1.exceptions">Exceptions</a> </h6> <div class="variablelist"> <p class="title"><b></b></p> <dl> <dt><span class="term">asio::system_error</span></dt> <dd><p> Thrown on failure. </p></dd> </dl> </div> <h6> <a name="asio.reference.read_at.overload1.h3"></a> <span><a name="asio.reference.read_at.overload1.example"></a></span><a class="link" href="overload1.html#asio.reference.read_at.overload1.example">Example</a> </h6> <p> To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a> function as follows: </p> <pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">read_at</span><span class="special">(</span><span class="identifier">d</span><span class="special">,</span> <span class="number">42</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">size</span><span class="special">));</span> </pre> <p> See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a> documentation for information on reading into multiple buffers in one go, and how to use it with arrays, boost::array or std::vector. </p> <h6> <a name="asio.reference.read_at.overload1.h4"></a> <span><a name="asio.reference.read_at.overload1.remarks"></a></span><a class="link" href="overload1.html#asio.reference.read_at.overload1.remarks">Remarks</a> </h6> <p> This overload is equivalent to calling: </p> <pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">read_at</span><span class="special">(</span> <span class="identifier">d</span><span class="special">,</span> <span class="number">42</span><span class="special">,</span> <span class="identifier">buffers</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_all</span><span class="special">());</span> </pre> </div> <div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p> Distributed under the Boost Software License, Version 1.0. (See accompanying 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>) </p> </div> <hr> <div class="spirit-nav"> <a accesskey="p" href="../read_at.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../read_at.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload2.html"><img src="../../../next.png" alt="Next"></a> </div> </body> </html>