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<div class="refentry" title="Class template weak_ptr">
<a name="boost.interprocess.weak_ptr"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Class template weak_ptr</span></h2>
<p>boost::interprocess::weak_ptr</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="emphasis"><em>// In header: <<a class="link" href="../../boost_interprocess_reference.html#header.boost.interprocess.smart_ptr.weak_ptr_hpp" title="Header <boost/interprocess/smart_ptr/weak_ptr.hpp>">boost/interprocess/smart_ptr/weak_ptr.hpp</a>>
</em></span><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> T, <span class="bold"><strong>typename</strong></span> A, <span class="bold"><strong>typename</strong></span> D>
<span class="bold"><strong>class</strong></span> <a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a> {
<span class="bold"><strong>public</strong></span>:
<span class="emphasis"><em>// types</em></span>
<span class="bold"><strong>typedef</strong></span> T <a name="boost.interprocess.weak_ptr.element_type"></a>element_type;
<span class="bold"><strong>typedef</strong></span> T <a name="boost.interprocess.weak_ptr.value_type"></a>value_type;
<span class="emphasis"><em>// <a class="link" href="weak_ptr.html#boost.interprocess.weak_ptrconstruct-copy-destruct">construct/copy/destruct</a></em></span>
<a class="link" href="weak_ptr.html#id819097-bb">weak_ptr</a>();
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> <a class="link" href="weak_ptr.html#id819103-bb">weak_ptr</a>(<a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> &);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> <a class="link" href="weak_ptr.html#id819131-bb">weak_ptr</a>(<a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> &);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> weak_ptr& <a class="link" href="weak_ptr.html#id819159-bb"><span class="bold"><strong>operator</strong></span>=</a>(<a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> &);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> weak_ptr& <a class="link" href="weak_ptr.html#id819186-bb"><span class="bold"><strong>operator</strong></span>=</a>(<a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> &);
<span class="emphasis"><em>// <a class="link" href="weak_ptr.html#id819007-bb">public member functions</a></em></span>
<span class="type"><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< T, A, D ></span> <a class="link" href="weak_ptr.html#id819011-bb">lock</a>() <span class="bold"><strong>const</strong></span>;
<span class="type"><span class="bold"><strong>long</strong></span></span> <a class="link" href="weak_ptr.html#id819028-bb">use_count</a>() <span class="bold"><strong>const</strong></span>;
<span class="type"><span class="bold"><strong>bool</strong></span></span> <a class="link" href="weak_ptr.html#id819048-bb">expired</a>() <span class="bold"><strong>const</strong></span>;
<span class="type"><span class="bold"><strong>void</strong></span></span> <a class="link" href="weak_ptr.html#id819065-bb">reset</a>() ;
<span class="type"><span class="bold"><strong>void</strong></span></span> <a class="link" href="weak_ptr.html#id819077-bb">swap</a>(this_type &) ;
};</pre></div>
<div class="refsect1" title="Description">
<a name="id1049697"></a><h2>Description</h2>
<p>The weak_ptr class template stores a "weak reference" to an object that's already managed by a shared_ptr. To access the object, a weak_ptr can be converted to a shared_ptr using the shared_ptr constructor or the member function lock. When the last shared_ptr to the object goes away and the object is deleted, the attempt to obtain a shared_ptr from the weak_ptr instances that refer to the deleted object will fail: the constructor will throw an exception of type bad_weak_ptr, and weak_ptr::lock will return an empty shared_ptr.</p>
<p>Every weak_ptr meets the CopyConstructible and Assignable requirements of the C++ Standard Library, and so can be used in standard library containers. Comparison operators are supplied so that weak_ptr works with the standard library's associative containers.</p>
<p>weak_ptr operations never throw exceptions.</p>
<p>The class template is parameterized on T, the type of the object pointed to. </p>
<div class="refsect2" title="weak_ptr public construct/copy/destruct">
<a name="id1049715"></a><h3>
<a name="boost.interprocess.weak_ptrconstruct-copy-destruct"></a><code class="computeroutput">weak_ptr</code>
public
construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="id819097-bb"></a>weak_ptr();</pre>
<p>Effects: Constructs an empty weak_ptr. Postconditions: use_count() == 0. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> <a name="id819103-bb"></a>weak_ptr(<a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> & r);</pre>
<p>Effects: If r is empty, constructs an empty weak_ptr; otherwise, constructs a weak_ptr that shares ownership with r as if by storing a copy of the pointer stored in r.</p>
<p>Postconditions: use_count() == r.use_count().</p>
<p>Throws: nothing. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> <a name="id819131-bb"></a>weak_ptr(<a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> & r);</pre>
<p>Effects: If r is empty, constructs an empty weak_ptr; otherwise, constructs a weak_ptr that shares ownership with r as if by storing a copy of the pointer stored in r.</p>
<p>Postconditions: use_count() == r.use_count().</p>
<p>Throws: nothing. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> weak_ptr& <a name="id819159-bb"></a><span class="bold"><strong>operator</strong></span>=(<a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> & r);</pre>
<p>Effects: Equivalent to weak_ptr(r).swap(*this).</p>
<p>Throws: nothing.</p>
<p>Notes: The implementation is free to meet the effects (and the implied guarantees) via different means, without creating a temporary. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Y> weak_ptr& <a name="id819186-bb"></a><span class="bold"><strong>operator</strong></span>=(<a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< Y, A, D > <span class="bold"><strong>const</strong></span> & r);</pre>
<p>Effects: Equivalent to weak_ptr(r).swap(*this).</p>
<p>Throws: nothing.</p>
<p>Notes: The implementation is free to meet the effects (and the implied guarantees) via different means, without creating a temporary. </p>
</li>
</ol></div>
</div>
<div class="refsect2" title="weak_ptr public member functions">
<a name="id1049959"></a><h3>
<a name="id819007-bb"></a><code class="computeroutput">weak_ptr</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="type"><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a>< T, A, D ></span> <a name="id819011-bb"></a>lock() <span class="bold"><strong>const</strong></span>;</pre>
<p>Returns: expired()? shared_ptr<T>(): shared_ptr<T>(*this).</p>
<p>Throws: nothing. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="type"><span class="bold"><strong>long</strong></span></span> <a name="id819028-bb"></a>use_count() <span class="bold"><strong>const</strong></span>;</pre>
<p>Returns: 0 if *this is empty; otherwise, the number of shared_ptr objects that share ownership with *this.</p>
<p>Throws: nothing.</p>
<p>Notes: use_count() is not necessarily efficient. Use only for debugging and testing purposes, not for production code. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id819048-bb"></a>expired() <span class="bold"><strong>const</strong></span>;</pre>
<p>Returns: Returns: use_count() == 0.</p>
<p>Throws: nothing.</p>
<p>Notes: expired() may be faster than use_count(). </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id819065-bb"></a>reset() ;</pre>
<p>Effects: Equivalent to: weak_ptr().swap(*this). </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id819077-bb"></a>swap(this_type & other) ;</pre>
<p>Effects: Exchanges the contents of the two smart pointers.</p>
<p>Throws: nothing. </p>
</li>
</ol></div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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