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| <div class="refentry"> |
| <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="comment">// 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>> |
| |
| </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="keyword">typename</span> A<span class="special">,</span> <span class="keyword">typename</span> D<span class="special">></span> |
| <span class="keyword">class</span> <a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a> <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">// types</span> |
| <span class="keyword">typedef</span> <span class="identifier">T</span> <a name="boost.interprocess.weak_ptr.element_type"></a><span class="identifier">element_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">T</span> <a name="boost.interprocess.weak_ptr.value_type"></a><span class="identifier">value_type</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="weak_ptr.html#boost.interprocess.weak_ptrconstruct-copy-destruct">construct/copy/destruct</a></span> |
| <a class="link" href="weak_ptr.html#id826798-bb"><span class="identifier">weak_ptr</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> <a class="link" href="weak_ptr.html#id826803-bb"><span class="identifier">weak_ptr</span></a><span class="special">(</span><a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> <a class="link" href="weak_ptr.html#id826831-bb"><span class="identifier">weak_ptr</span></a><span class="special">(</span><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> weak_ptr& <a class="link" href="weak_ptr.html#id826859-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> weak_ptr& <a class="link" href="weak_ptr.html#id826887-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="weak_ptr.html#id826708-bb">public member functions</a></span> |
| <a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <a class="link" href="weak_ptr.html#id826711-bb"><span class="identifier">lock</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">long</span> <a class="link" href="weak_ptr.html#id826728-bb"><span class="identifier">use_count</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">bool</span> <a class="link" href="weak_ptr.html#id826748-bb"><span class="identifier">expired</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">void</span> <a class="link" href="weak_ptr.html#id826765-bb"><span class="identifier">reset</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">void</span> <a class="link" href="weak_ptr.html#id826777-bb"><span class="identifier">swap</span></a><span class="special">(</span><span class="identifier">this_type</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="special">}</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="id1520617"></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"> |
| <a name="id1520635"></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="id826798-bb"></a><span class="identifier">weak_ptr</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> |
| <p>Effects: Constructs an empty weak_ptr. Postconditions: use_count() == 0. </p> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> <a name="id826803-bb"></a><span class="identifier">weak_ptr</span><span class="special">(</span><a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> r<span class="special">)</span><span class="special">;</span></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="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> <a name="id826831-bb"></a><span class="identifier">weak_ptr</span><span class="special">(</span><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> r<span class="special">)</span><span class="special">;</span></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="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> weak_ptr& <a name="id826859-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><a class="link" href="weak_ptr.html" title="Class template weak_ptr">weak_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> r<span class="special">)</span><span class="special">;</span></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="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Y<span class="special">></span> weak_ptr& <a name="id826887-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">Y</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> r<span class="special">)</span><span class="special">;</span></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"> |
| <a name="id1521150"></a><h3> |
| <a name="id826708-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"><a class="link" href="shared_ptr.html" title="Class template shared_ptr">shared_ptr</a><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">></span> <a name="id826711-bb"></a><span class="identifier">lock</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</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="keyword">long</span> <a name="id826728-bb"></a><span class="identifier">use_count</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</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="keyword">bool</span> <a name="id826748-bb"></a><span class="identifier">expired</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</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="keyword">void</span> <a name="id826765-bb"></a><span class="identifier">reset</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> |
| <p>Effects: Equivalent to: weak_ptr().swap(*this). </p> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">void</span> <a name="id826777-bb"></a><span class="identifier">swap</span><span class="special">(</span><span class="identifier">this_type</span> <span class="special">&</span> other<span class="special">)</span><span class="special">;</span></pre> |
| <p>Effects: Exchanges the contents of the two smart pointers.</p> |
| <p>Throws: nothing. </p> |
| </li> |
| </ol></div> |
| </div> |
| </div> |
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