1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Timer.4 - Using a member function as a handler</title>
<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
<link rel="home" href="../../boost_asio.html" title="Boost.Asio">
<link rel="up" href="../tutorial.html" title="Tutorial">
<link rel="prev" href="tuttimer3/src.html" title="Source listing for Timer.3">
<link rel="next" href="tuttimer4/src.html" title="Source listing for Timer.4">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
<td align="center"><a href="../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="tuttimer3/src.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tuttimer4/src.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.tutorial.tuttimer4"></a><a class="link" href="tuttimer4.html" title="Timer.4 - Using a member function as a handler">Timer.4 - Using a member
function as a handler</a>
</h3></div></div></div>
<p>
In this tutorial we will see how to use a class member function as a callback
handler. The program should execute identically to the tutorial program from
tutorial Timer.3.
</p>
<pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span>
<span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">bind</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">date_time</span><span class="special">/</span><span class="identifier">posix_time</span><span class="special">/</span><span class="identifier">posix_time</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Instead of defining a free function <code class="computeroutput"><span class="identifier">print</span></code>
as the callback handler, as we did in the earlier tutorial programs, we now
define a class called <code class="computeroutput"><span class="identifier">printer</span></code>.
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">printer</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
</pre>
<p>
The constructor of this class will take a reference to the io_service object
and use it when initialising the <code class="computeroutput"><span class="identifier">timer_</span></code>
member. The counter used to shut down the program is now also a member of
the class.
</p>
<pre class="programlisting"> <span class="identifier">printer</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">&</span> <span class="identifier">io</span><span class="special">)</span>
<span class="special">:</span> <span class="identifier">timer_</span><span class="special">(</span><span class="identifier">io</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span>
<span class="identifier">count_</span><span class="special">(</span><span class="number">0</span><span class="special">)</span>
<span class="special">{</span>
</pre>
<p>
The boost::bind() function works just as well with class member functions
as with free functions. Since all non-static class member functions have
an implicit <code class="computeroutput"><span class="keyword">this</span></code> parameter,
we need to bind <code class="computeroutput"><span class="keyword">this</span></code> to the
function. As in tutorial Timer.3, boost::bind() converts our callback handler
(now a member function) into a function object that can be invoked as though
it has the signature <code class="computeroutput"><span class="keyword">void</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&)</span></code>.
</p>
<p>
You will note that the boost::asio::placeholders::error placeholder is not
specified here, as the <code class="computeroutput"><span class="identifier">print</span></code>
member function does not accept an error object as a parameter.
</p>
<pre class="programlisting"> <span class="identifier">timer_</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&</span><span class="identifier">printer</span><span class="special">::</span><span class="identifier">print</span><span class="special">,</span> <span class="keyword">this</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p>
In the class destructor we will print out the final value of the counter.
</p>
<pre class="programlisting"> <span class="special">~</span><span class="identifier">printer</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Final count is "</span> <span class="special"><<</span> <span class="identifier">count_</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
The <code class="computeroutput"><span class="identifier">print</span></code> member function
is very similar to the <code class="computeroutput"><span class="identifier">print</span></code>
function from tutorial Timer.3, except that it now operates on the class
data members instead of having the timer and counter passed in as parameters.
</p>
<pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">print</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">count_</span> <span class="special"><</span> <span class="number">5</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">count_</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">++</span><span class="identifier">count_</span><span class="special">;</span>
<span class="identifier">timer_</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">timer_</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
<span class="identifier">timer_</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&</span><span class="identifier">printer</span><span class="special">::</span><span class="identifier">print</span><span class="special">,</span> <span class="keyword">this</span><span class="special">));</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">deadline_timer</span> <span class="identifier">timer_</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">count_</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<p>
The <code class="computeroutput"><span class="identifier">main</span></code> function is much
simpler than before, as it now declares a local <code class="computeroutput"><span class="identifier">printer</span></code>
object before running the io_service as normal.
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io</span><span class="special">;</span>
<span class="identifier">printer</span> <span class="identifier">p</span><span class="special">(</span><span class="identifier">io</span><span class="special">);</span>
<span class="identifier">io</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
See the <a class="link" href="tuttimer4/src.html" title="Source listing for Timer.4">full source listing</a>
</p>
<p>
Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
</p>
<p>
Previous: <a class="link" href="tuttimer3.html" title="Timer.3 - Binding arguments to a handler">Timer.3 - Binding
arguments to a handler</a>
</p>
<p>
Next: <a class="link" href="tuttimer5.html" title="Timer.5 - Synchronising handlers in multithreaded programs">Timer.5 - Synchronising
handlers in multithreaded programs</a>
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2015 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></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="tuttimer3/src.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tuttimer4/src.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|