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<title>enable_shared_from_this</title>
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<h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png"
width="277" align="middle" border="0">enable_shared_from_this</h1>
<h2><a name="Purpose">Purpose</a></h2>
<p>
The header <STRONG>&lt;boost/enable_shared_from_this.hpp&gt;</STRONG> defines
the class template <STRONG>enable_shared_from_this</STRONG>. It is used as a
base class that allows a <A href="shared_ptr.htm">shared_ptr</A> to the current
object to be obtained from within a member function.
</p>
<P><STRONG>enable_shared_from_this&lt;T&gt;</STRONG> defines two member functions
called <STRONG>shared_from_this</STRONG> that return a <STRONG>shared_ptr&lt;T&gt;</STRONG>
and <STRONG>shared_ptr&lt;T const&gt;</STRONG>, depending on constness, to <STRONG>this</STRONG>.</P>
<h2><a name="Example">Example</a></h2>
<pre>
#include &lt;boost/enable_shared_from_this.hpp&gt;
#include &lt;boost/shared_ptr.hpp&gt;
#include &lt;cassert&gt;
class Y: public boost::enable_shared_from_this&lt;Y&gt;
{
public:
boost::shared_ptr&lt;Y&gt; f()
{
return shared_from_this();
}
};
int main()
{
boost::shared_ptr&lt;Y&gt; p(new Y);
boost::shared_ptr&lt;Y&gt; q = p-&gt;f();
assert(p == q);
assert(!(p &lt; q || q &lt; p)); // p and q must share ownership
}
</pre>
<h3><a name="Synopsis">Synopsis</a></h3>
<pre>
namespace boost
{
template&lt;class T&gt; class enable_shared_from_this
{
public:
shared_ptr&lt;T&gt; shared_from_this();
shared_ptr&lt;T const&gt; shared_from_this() const;
}
}
</pre>
<h4>template&lt;class T&gt; shared_ptr&lt;T&gt;
enable_shared_from_this&lt;T&gt;::shared_from_this();</h4>
<h4>template&lt;class T&gt; shared_ptr&lt;T const&gt;
enable_shared_from_this&lt;T&gt;::shared_from_this() const;</h4>
<blockquote>
<p>
<b>Requires:</b> <STRONG>enable_shared_from_this&lt;T&gt;</STRONG> must be an
accessible base class of <b>T</b>. <STRONG>*this</STRONG> must be a subobject
of an instance <STRONG>t</STRONG> of type <STRONG>T</STRONG> . There must exist
at least one <STRONG>shared_ptr</STRONG> instance <STRONG>p</STRONG> that <EM>owns</EM>
<STRONG>t</STRONG>.
</p>
<p>
<b>Returns:</b> A <b>shared_ptr&lt;T&gt;</b> instance <b>r</b> that shares
ownership with <b>p</b>.
</p>
<p>
<b>Postconditions:</b> <tt>r.get() == this</tt>.
</p>
</blockquote>
<p>$Date$</p>
<p>
<small>Copyright &copy; 2002, 2003 by Peter Dimov. Distributed under the Boost Software License, Version
1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
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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