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1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
| 2 | <html> | |
| 3 | <head> | |
| 4 | <title>enable_shared_from_this</title> | |
| 5 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> | |
| 6 | </head> | |
| 7 | <body text="#000000" bgcolor="#ffffff" link="#0000ff" vlink="#0000ff"> | |
| 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 <code><boost/enable_shared_from_this.hpp></code> defines | |
| 13 | the class template <code>enable_shared_from_this</code>. It is used as a | |
| 14 | base class that allows a <a href="shared_ptr.htm">shared_ptr</a> or | |
| 15 | a <a href="weak_ptr.htm">weak_ptr</a> to the current object to be obtained | |
| 16 | from within a member function. | |
| 17 | </p> | |
| 18 | <p><code>enable_shared_from_this<T></code> defines two member functions | |
| 19 | called <code>shared_from_this</code> that return a <code>shared_ptr<T></code> | |
| 20 | and <code>shared_ptr<T const></code>, depending on constness, to <code>this</code>. | |
| 21 | It also defines two member functions called <code>weak_from_this</code> that return | |
| 22 | a corresponding <code>weak_ptr</code>. | |
| 23 | </p> | |
| 24 | <h2><a name="Example">Example</a></h2> | |
| 25 | <pre> | |
| 26 | #include <boost/enable_shared_from_this.hpp> | |
| 27 | #include <boost/shared_ptr.hpp> | |
| 28 | #include <cassert> | |
| 29 | ||
| 30 | class Y: public boost::enable_shared_from_this<Y> | |
| 31 | { | |
| 32 | public: | |
| 33 | ||
| 34 | boost::shared_ptr<Y> f() | |
| 35 | { | |
| 36 | return shared_from_this(); | |
| 37 | } | |
| 38 | }; | |
| 39 | ||
| 40 | int main() | |
| 41 | { | |
| 42 | boost::shared_ptr<Y> p(new Y); | |
| 43 | boost::shared_ptr<Y> q = p->f(); | |
| 44 | assert(p == q); | |
| 45 | assert(!(p < q || q < p)); // p and q must share ownership | |
| 46 | } | |
| 47 | </pre> | |
| 48 | <h2><a name="Synopsis">Synopsis</a></h2> | |
| 49 | <pre> | |
| 50 | namespace boost | |
| 51 | { | |
| 52 | ||
| 53 | template<class T> class enable_shared_from_this | |
| 54 | { | |
| 55 | public: | |
| 56 | ||
| 57 | shared_ptr<T> shared_from_this(); | |
| 58 | shared_ptr<T const> shared_from_this() const; | |
| 59 | ||
| 60 | weak_ptr<T> weak_from_this() noexcept; | |
| 61 | weak_ptr<T const> weak_from_this() const noexcept; | |
| 62 | } | |
| 63 | ||
| 64 | } | |
| 65 | </pre> | |
| 66 | <h4><code>template<class T> shared_ptr<T> | |
| 67 | enable_shared_from_this<T>::shared_from_this();</code></h4> | |
| 68 | <h4><code>template<class T> shared_ptr<T const> | |
| 69 | enable_shared_from_this<T>::shared_from_this() const;</code></h4> | |
| 70 | <blockquote> | |
| 71 | <p> | |
| 72 | <b>Requires:</b> <code>enable_shared_from_this<T></code> must be an | |
| 73 | accessible base class of <code>T</code>. <code>*this</code> must be a subobject | |
| 74 | of an instance <code>t</code> of type <code>T</code>. | |
| 75 | </p> | |
| 76 | <p> | |
| 77 | <b>Returns:</b> If a <code>shared_ptr</code> instance <code>p</code> that <em>owns</em> | |
| 78 | <code>t</code> exists, a <code>shared_ptr<T></code> instance <code>r</code> that shares | |
| 79 | ownership with <code>p</code>. | |
| 80 | </p> | |
| 81 | <p> | |
| 82 | <b>Postconditions:</b> <code>r.get() == this</code>. | |
| 83 | </p> | |
| 84 | <p> | |
| 85 | <b>Throws:</b> <code>bad_weak_ptr</code> when no <code>shared_ptr</code> <em>owns</em> <code>*this</code>. | |
| 86 | </p> | |
| 87 | </blockquote> | |
| 88 | <h4><code>template<class T> weak_ptr<T> | |
| 89 | enable_shared_from_this<T>::weak_from_this() noexcept;</code></h4> | |
| 90 | <h4><code>template<class T> weak_ptr<T const> | |
| 91 | enable_shared_from_this<T>::weak_from_this() const noexcept;</code></h4> | |
| 92 | <blockquote> | |
| 93 | <p> | |
| 94 | <b>Requires:</b> <code>enable_shared_from_this<T></code> must be an | |
| 95 | accessible base class of <code>T</code>. <code>*this</code> must be a subobject | |
| 96 | of an instance <code>t</code> of type <code>T</code>. | |
| 97 | </p> | |
| 98 | <p> | |
| 99 | <b>Returns:</b> If a <code>shared_ptr</code> instance <code>p</code> that <em>owns</em> | |
| 100 | <code>t</code> exists or has existed in the past, a <code>weak_ptr<T></code> instance | |
| 101 | <code>r</code> that shares ownership with <code>p</code>. Otherwise, an empty <code>weak_ptr</code>. | |
| 102 | </p> | |
| 103 | </blockquote> | |
| 104 | <hr /> | |
| 105 | <p> | |
| 106 | <small>Copyright © 2002, 2003, 2015 by Peter Dimov. Distributed under the Boost Software License, Version | |
| 107 | 1.0. See accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or | |
| 108 | copy at <a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>.</small></p> | |
| 109 | </body> | |
| 110 | </html> |