libs/smart_ptr/enable_shared_from_this.html

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   4         <title>enable_shared_from_this</title>
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   8         <h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png"
   9             width="277" align="middle" border="0">enable_shared_from_this</h1>
  10         <h2><a name="Purpose">Purpose</a></h2>
  11         <p>
  12             The header <STRONG>&lt;boost/enable_shared_from_this.hpp&gt;</STRONG> defines
  13             the class template <STRONG>enable_shared_from_this</STRONG>. It is used as a
  14             base class that allows a <A href="shared_ptr.htm">shared_ptr</A> to the current
  15             object to be obtained from within a member function.
  16         </p>
  17         <P><STRONG>enable_shared_from_this&lt;T&gt;</STRONG> defines two member functions
  18             called <STRONG>shared_from_this</STRONG> that return a <STRONG>shared_ptr&lt;T&gt;</STRONG>
  19             and <STRONG>shared_ptr&lt;T const&gt;</STRONG>, depending on constness, to <STRONG>this</STRONG>.</P>
  20         <h2><a name="Example">Example</a></h2>
  21         <pre>
  22 #include &lt;boost/enable_shared_from_this.hpp&gt;
  23 #include &lt;boost/shared_ptr.hpp&gt;
  24 #include &lt;cassert&gt;
  25
  26 class Y: public boost::enable_shared_from_this&lt;Y&gt;
  27 {
  28 public:
  29
  30     boost::shared_ptr&lt;Y&gt; f()
  31     {
  32         return shared_from_this();
  33     }
  34 };
  35
  36 int main()
  37 {
  38     boost::shared_ptr&lt;Y&gt; p(new Y);
  39     boost::shared_ptr&lt;Y&gt; q = p-&gt;f();
  40     assert(p == q);
  41     assert(!(p &lt; q || q &lt; p)); // p and q must share ownership
  42 }
  43 </pre>
  44         <h3><a name="Synopsis">Synopsis</a></h3>
  45         <pre>
  46 namespace boost
  47 {
  48
  49 template&lt;class T&gt; class enable_shared_from_this
  50 {
  51 public:
  52
  53     shared_ptr&lt;T&gt; shared_from_this();
  54     shared_ptr&lt;T const&gt; shared_from_this() const;
  55 }
  56
  57 }
  58 </pre>
  59         <h4>template&lt;class T&gt; shared_ptr&lt;T&gt;
  60             enable_shared_from_this&lt;T&gt;::shared_from_this();</h4>
  61         <h4>template&lt;class T&gt; shared_ptr&lt;T const&gt;
  62             enable_shared_from_this&lt;T&gt;::shared_from_this() const;</h4>
  63         <blockquote>
  64             <p>
  65                 <b>Requires:</b> <STRONG>enable_shared_from_this&lt;T&gt;</STRONG> must be an
  66                 accessible base class of <b>T</b>. <STRONG>*this</STRONG> must be a subobject
  67                 of an instance <STRONG>t</STRONG> of type <STRONG>T</STRONG> . There must exist
  68                 at least one <STRONG>shared_ptr</STRONG> instance <STRONG>p</STRONG> that <EM>owns</EM>
  69                 <STRONG>t</STRONG>.
  70             </p>
  71             <p>
  72                 <b>Returns:</b> A <b>shared_ptr&lt;T&gt;</b> instance <b>r</b> that shares
  73                 ownership with <b>p</b>.
  74             </p>
  75             <p>
  76                 <b>Postconditions:</b> <tt>r.get() == this</tt>.
  77             </p>
  78         </blockquote>
  79         <p>$Date$</p>
  80         <p>
  81             <small>Copyright &copy; 2002, 2003 by Peter Dimov. Distributed under the Boost Software License, Version
  82                 1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
  83                 copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p>
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