171 lines
12 KiB
HTML
171 lines
12 KiB
HTML
|
<html>
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
|
||
|
|
<title>async_read (6 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="../async_read.html" title="async_read">
|
||
|
|
<link rel="prev" href="overload5.html" title="async_read (5 of 8 overloads)">
|
||
|
|
<link rel="next" href="overload7.html" title="async_read (7 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="overload5.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../async_read.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="overload7.html"><img src="../../../next.png" alt="Next"></a>
|
||
|
|
</div>
|
||
|
|
<div class="section">
|
||
|
|
<div class="titlepage"><div><div><h4 class="title">
|
||
|
|
<a name="asio.reference.async_read.overload6"></a><a class="link" href="overload6.html" title="async_read (6 of 8 overloads)">async_read (6
|
||
|
|
of 8 overloads)</a>
|
||
|
|
</h4></div></div></div>
|
||
|
|
<p>
|
||
|
|
Start an asynchronous operation to read a certain amount of data from a
|
||
|
|
stream.
|
||
|
|
</p>
|
||
|
|
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
|
||
|
|
<span class="keyword">typename</span> <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a><span class="special">,</span>
|
||
|
|
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
|
||
|
|
<span class="keyword">typename</span> <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a><span class="special">,</span>
|
||
|
|
<span class="keyword">typename</span> <a class="link" href="../ReadToken.html" title="Read token requirements">ReadToken</a> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">></span>
|
||
|
|
<a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">async_read</span><span class="special">(</span>
|
||
|
|
<span class="identifier">AsyncReadStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
|
||
|
|
<span class="identifier">basic_streambuf</span><span class="special"><</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
|
||
|
|
<span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
|
||
|
|
<span class="identifier">ReadToken</span> <span class="special">&&</span> <span class="identifier">token</span> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">);</span>
|
||
|
|
</pre>
|
||
|
|
<p>
|
||
|
|
This function is used to asynchronously read a certain number of bytes
|
||
|
|
of data from a stream. It is an initiating function for an <a class="link" href="../../overview/model/async_ops.html" title="Asynchronous Operations">asynchronous
|
||
|
|
operation</a>, and always returns immediately. The asynchronous operation
|
||
|
|
will continue until one of the following conditions is true:
|
||
|
|
</p>
|
||
|
|
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
|
||
|
|
<li class="listitem">
|
||
|
|
The supplied buffer is full (that is, it has reached maximum size).
|
||
|
|
</li>
|
||
|
|
<li class="listitem">
|
||
|
|
The completion_condition function object returns 0.
|
||
|
|
</li>
|
||
|
|
</ul></div>
|
||
|
|
<p>
|
||
|
|
This operation is implemented in terms of zero or more calls to the stream's
|
||
|
|
async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
|
||
|
|
The program must ensure that the stream performs no other read operations
|
||
|
|
(such as async_read, the stream's async_read_some function, or any other
|
||
|
|
composed operations that perform reads) until this operation completes.
|
||
|
|
</p>
|
||
|
|
<h6>
|
||
|
|
<a name="asio.reference.async_read.overload6.h0"></a>
|
||
|
|
<span><a name="asio.reference.async_read.overload6.parameters"></a></span><a class="link" href="overload6.html#asio.reference.async_read.overload6.parameters">Parameters</a>
|
||
|
|
</h6>
|
||
|
|
<div class="variablelist">
|
||
|
|
<p class="title"><b></b></p>
|
||
|
|
<dl>
|
||
|
|
<dt><span class="term">s</span></dt>
|
||
|
|
<dd><p>
|
||
|
|
The stream from which the data is to be read. The type must support
|
||
|
|
the AsyncReadStream concept.
|
||
|
|
</p></dd>
|
||
|
|
<dt><span class="term">b</span></dt>
|
||
|
|
<dd><p>
|
||
|
|
A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a>
|
||
|
|
object into which the data will be read. Ownership of the streambuf
|
||
|
|
is retained by the caller, which must guarantee that it remains valid
|
||
|
|
until the completion handler is called.
|
||
|
|
</p></dd>
|
||
|
|
<dt><span class="term">completion_condition</span></dt>
|
||
|
|
<dd>
|
||
|
|
<p>
|
||
|
|
The function object to be called to determine whether the read operation
|
||
|
|
is complete. The signature of the function object must be:
|
||
|
|
</p>
|
||
|
|
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">completion_condition</span><span class="special">(</span>
|
||
|
|
<span class="comment">// Result of latest async_read_some operation.</span>
|
||
|
|
<span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span>
|
||
|
|
|
||
|
|
<span class="comment">// Number of bytes transferred so far.</span>
|
||
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
|
||
|
|
<span class="special">);</span>
|
||
|
|
</pre>
|
||
|
|
<p>
|
||
|
|
A return value of 0 indicates that the read operation is complete.
|
||
|
|
A non-zero return value indicates the maximum number of bytes to
|
||
|
|
be read on the next call to the stream's async_read_some function.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><span class="term">token</span></dt>
|
||
|
|
<dd>
|
||
|
|
<p>
|
||
|
|
The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
|
||
|
|
token</a> that will be used to produce a completion handler, which
|
||
|
|
will be called when the read completes. Potential completion tokens
|
||
|
|
include <a class="link" href="../use_future.html" title="use_future"><code class="computeroutput"><span class="identifier">use_future</span></code></a>,
|
||
|
|
<a class="link" href="../use_awaitable.html" title="use_awaitable"><code class="computeroutput"><span class="identifier">use_awaitable</span></code></a>,
|
||
|
|
<a class="link" href="../yield_context.html" title="yield_context"><code class="computeroutput"><span class="identifier">yield_context</span></code></a>,
|
||
|
|
or a function object with the correct completion signature. The function
|
||
|
|
signature of the completion handler must be:
|
||
|
|
</p>
|
||
|
|
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
|
||
|
|
<span class="comment">// Result of operation.</span>
|
||
|
|
<span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span>
|
||
|
|
|
||
|
|
<span class="comment">// Number of bytes copied into the buffers. If an error</span>
|
||
|
|
<span class="comment">// occurred, this will be the number of bytes successfully</span>
|
||
|
|
<span class="comment">// transferred prior to the error.</span>
|
||
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
|
||
|
|
<span class="special">);</span>
|
||
|
|
</pre>
|
||
|
|
<p>
|
||
|
|
Regardless of whether the asynchronous operation completes immediately
|
||
|
|
or not, the completion handler will not be invoked from within this
|
||
|
|
function. On immediate completion, invocation of the handler will
|
||
|
|
be performed in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput"><span class="identifier">post</span></code></a>.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
</div>
|
||
|
|
<h6>
|
||
|
|
<a name="asio.reference.async_read.overload6.h1"></a>
|
||
|
|
<span><a name="asio.reference.async_read.overload6.completion_signature"></a></span><a class="link" href="overload6.html#asio.reference.async_read.overload6.completion_signature">Completion
|
||
|
|
Signature</a>
|
||
|
|
</h6>
|
||
|
|
<pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">)</span>
|
||
|
|
</pre>
|
||
|
|
<h6>
|
||
|
|
<a name="asio.reference.async_read.overload6.h2"></a>
|
||
|
|
<span><a name="asio.reference.async_read.overload6.per_operation_cancellation"></a></span><a class="link" href="overload6.html#asio.reference.async_read.overload6.per_operation_cancellation">Per-Operation
|
||
|
|
Cancellation</a>
|
||
|
|
</h6>
|
||
|
|
<p>
|
||
|
|
This asynchronous operation supports cancellation for the following <a class="link" href="../cancellation_type.html" title="cancellation_type"><code class="computeroutput"><span class="identifier">cancellation_type</span></code></a>
|
||
|
|
values:
|
||
|
|
</p>
|
||
|
|
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
|
||
|
|
<li class="listitem">
|
||
|
|
<code class="computeroutput"><span class="identifier">cancellation_type</span><span class="special">::</span><span class="identifier">terminal</span></code>
|
||
|
|
</li>
|
||
|
|
<li class="listitem">
|
||
|
|
<code class="computeroutput"><span class="identifier">cancellation_type</span><span class="special">::</span><span class="identifier">partial</span></code>
|
||
|
|
</li>
|
||
|
|
</ul></div>
|
||
|
|
<p>
|
||
|
|
if they are also supported by the <code class="computeroutput"><span class="identifier">AsyncReadStream</span></code>
|
||
|
|
type's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
|
||
|
|
operation.
|
||
|
|
</p>
|
||
|
|
</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="overload5.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../async_read.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="overload7.html"><img src="../../../next.png" alt="Next"></a>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|