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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 <code><boost/enable_shared_from_this.hpp></code> defines |
| the class template <code>enable_shared_from_this</code>. It is used as a |
| base class that allows a <a href="shared_ptr.htm">shared_ptr</a> or |
| a <a href="weak_ptr.htm">weak_ptr</a> to the current object to be obtained |
| from within a member function. |
| </p> |
| <p><code>enable_shared_from_this<T></code> defines two member functions |
| called <code>shared_from_this</code> that return a <code>shared_ptr<T></code> |
| and <code>shared_ptr<T const></code>, depending on constness, to <code>this</code>. |
| It also defines two member functions called <code>weak_from_this</code> that return |
| a corresponding <code>weak_ptr</code>. |
| </p> |
| <h2><a name="Example">Example</a></h2> |
| <pre> |
| #include <boost/enable_shared_from_this.hpp> |
| #include <boost/shared_ptr.hpp> |
| #include <cassert> |
| |
| class Y: public boost::enable_shared_from_this<Y> |
| { |
| public: |
| |
| boost::shared_ptr<Y> f() |
| { |
| return shared_from_this(); |
| } |
| }; |
| |
| int main() |
| { |
| boost::shared_ptr<Y> p(new Y); |
| boost::shared_ptr<Y> q = p->f(); |
| assert(p == q); |
| assert(!(p < q || q < p)); // p and q must share ownership |
| } |
| </pre> |
| <h2><a name="Synopsis">Synopsis</a></h2> |
| <pre> |
| namespace boost |
| { |
| |
| template<class T> class enable_shared_from_this |
| { |
| public: |
| |
| shared_ptr<T> shared_from_this(); |
| shared_ptr<T const> shared_from_this() const; |
| |
| weak_ptr<T> weak_from_this() noexcept; |
| weak_ptr<T const> weak_from_this() const noexcept; |
| } |
| |
| } |
| </pre> |
| <h4><code>template<class T> shared_ptr<T> |
| enable_shared_from_this<T>::shared_from_this();</code></h4> |
| <h4><code>template<class T> shared_ptr<T const> |
| enable_shared_from_this<T>::shared_from_this() const;</code></h4> |
| <blockquote> |
| <p> |
| <b>Requires:</b> <code>enable_shared_from_this<T></code> must be an |
| accessible base class of <code>T</code>. <code>*this</code> must be a subobject |
| of an instance <code>t</code> of type <code>T</code>. |
| </p> |
| <p> |
| <b>Returns:</b> If a <code>shared_ptr</code> instance <code>p</code> that <em>owns</em> |
| <code>t</code> exists, a <code>shared_ptr<T></code> instance <code>r</code> that shares |
| ownership with <code>p</code>. |
| </p> |
| <p> |
| <b>Postconditions:</b> <code>r.get() == this</code>. |
| </p> |
| <p> |
| <b>Throws:</b> <code>bad_weak_ptr</code> when no <code>shared_ptr</code> <em>owns</em> <code>*this</code>. |
| </p> |
| </blockquote> |
| <h4><code>template<class T> weak_ptr<T> |
| enable_shared_from_this<T>::weak_from_this() noexcept;</code></h4> |
| <h4><code>template<class T> weak_ptr<T const> |
| enable_shared_from_this<T>::weak_from_this() const noexcept;</code></h4> |
| <blockquote> |
| <p> |
| <b>Requires:</b> <code>enable_shared_from_this<T></code> must be an |
| accessible base class of <code>T</code>. <code>*this</code> must be a subobject |
| of an instance <code>t</code> of type <code>T</code>. |
| </p> |
| <p> |
| <b>Returns:</b> If a <code>shared_ptr</code> instance <code>p</code> that <em>owns</em> |
| <code>t</code> exists or has existed in the past, a <code>weak_ptr<T></code> instance |
| <code>r</code> that shares ownership with <code>p</code>. Otherwise, an empty <code>weak_ptr</code>. |
| </p> |
| </blockquote> |
| <hr /> |
| <p> |
| <small>Copyright © 2002, 2003, 2015 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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