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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>intrusive_ptr</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body text="#000000" bgcolor="#ffffff" link="#0000ff" vlink="#0000ff"> <h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png" width="277" align="middle" border="0">intrusive_ptr class template</h1> <a href="#Introduction">Introduction</a> <a href="#Synopsis">Synopsis</a> <a href="#Members">Members</a> <a href="#functions">Free Functions</a> <h2><a name="Introduction">Introduction</a></h2> The <code>intrusive_ptr</code> class template stores a pointer to an object with an embedded reference count. Every new <code>intrusive_ptr</code> instance increments the reference count by using an unqualified call to the function <code>intrusive_ptr_add_ref</code>, passing it the pointer as an argument. Similarly, when an <code>intrusive_ptr</code> is destroyed, it calls <code>intrusive_ptr_release</code>; this function is responsible for destroying the object when its reference count drops to zero. The user is expected to provide suitable definitions of these two functions. On compilers that support argument-dependent lookup, <code>intrusive_ptr_add_ref</code> and <code>intrusive_ptr_release</code> should be defined in the namespace that corresponds to their parameter; otherwise, the definitions need to go in namespace <code>boost</code>. The library provides a helper base class template <code><a href="intrusive_ref_counter.html">intrusive_ref_counter</a></code> which may help adding support for <code>intrusive_ptr</code> to user types. The class template is parameterized on <code>T</code>, the type of the object pointed to. <code>intrusive_ptr<T></code> can be implicitly converted to <code>intrusive_ptr</code> whenever <code>T*</code> can be implicitly converted to <code>U*</code>. The main reasons to use <code>intrusive_ptr</code> are: <ul> <li> Some existing frameworks or OSes provide objects with embedded reference counts;</li> <li> The memory footprint of <code>intrusive_ptr</code> is the same as the corresponding raw pointer;</li> <li> <code>intrusive_ptr<T></code> can be constructed from an arbitrary raw pointer of type <code>T *</code>.</li></ul> As a general rule, if it isn't obvious whether <code>intrusive_ptr</code> better fits your needs than <code>shared_ptr</code>, try a <code>shared_ptr</code>-based design first. <h2><a name="Synopsis">Synopsis</a></h2> <pre>namespace boost { template<class T> class intrusive_ptr { public: typedef T <a href="#element_type" >element_type</a>; <a href="#constructors" >intrusive_ptr</a>(); // never throws <a href="#constructors" >intrusive_ptr</a>(T * p, bool add_ref = true); <a href="#constructors" >intrusive_ptr</a>(intrusive_ptr const & r); template<class Y> <a href="#constructors" >intrusive_ptr</a>(intrusive_ptr<Y> const & r); <a href="#destructor" >~intrusive_ptr</a>(); intrusive_ptr & <a href="#assignment" >operator=</a>(intrusive_ptr const & r); template<class Y> intrusive_ptr & <a href="#assignment" >operator=</a>(intrusive_ptr<Y> const & r); intrusive_ptr & <a href="#assignment" >operator=</a>(T * r); void <a href="#reset" >reset</a>(); void <a href="#reset" >reset</a>(T * r); void <a href="#reset" >reset</a>(T * r, bool add_ref); T & <a href="#indirection" >operator*</a>() const; // never throws T * <a href="#indirection" >operator-></a>() const; // never throws T * <a href="#get" >get</a>() const; // never throws T * <a href="#detach" >detach</a>(); // never throws operator <a href="#conversions" >unspecified-bool-type</a>() const; // never throws void <a href="#swap" >swap</a>(intrusive_ptr & b); // never throws }; template<class T, class U> bool <a href="#comparison" >operator==</a>(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws template<class T, class U> bool <a href="#comparison" >operator!=</a>(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws template<class T> bool <a href="#comparison" >operator==</a>(intrusive_ptr<T> const & a, T * b); // never throws template<class T> bool <a href="#comparison" >operator!=</a>(intrusive_ptr<T> const & a, T * b); // never throws template<class T> bool <a href="#comparison" >operator==</a>(T * a, intrusive_ptr<T> const & b); // never throws template<class T> bool <a href="#comparison" >operator!=</a>(T * a, intrusive_ptr<T> const & b); // never throws template<class T, class U> bool <a href="#comparison" >operator<</a>(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws template<class T> void <a href="#free-swap" >swap</a>(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws template<class T> T * <a href="#get_pointer" >get_pointer</a>(intrusive_ptr<T> const & p); // never throws template<class T, class U> intrusive_ptr<T> <a href="#static_pointer_cast" >static_pointer_cast</a>(intrusive_ptr const & r); // never throws template<class T, class U> intrusive_ptr<T> <a href="#const_pointer_cast" >const_pointer_cast</a>(intrusive_ptr const & r); // never throws template<class T, class U> intrusive_ptr<T> <a href="#dynamic_pointer_cast" >dynamic_pointer_cast</a>(intrusive_ptr const & r); // never throws template<class E, class T, class Y> std::basic_ostream<E, T> & <a href="#insertion-operator" >operator<<</a> (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p); }</pre> <h2><a name="Members">Members</a></h2> <h3><a name="element_type">element_type</a></h3> <pre>typedef T element_type;</pre> <blockquote> Provides the type of the template parameter <code>T</code>. </blockquote> <h3><a name="constructors">constructors</a></h3> <pre>intrusive_ptr(); // never throws</pre> <blockquote> Postconditions: <code>get() == 0</code>. Throws: nothing. </blockquote> <pre>intrusive_ptr(T * p, bool add_ref = true);</pre> <blockquote> Effects: <code>if(p != 0 && add_ref) intrusive_ptr_add_ref(p);</code>. Postconditions: <code>get() == p</code>. </blockquote> <pre>intrusive_ptr(intrusive_ptr const & r); template<class Y> intrusive_ptr(intrusive_ptr<Y> const & r);</pre> <blockquote> Effects: <code>if(r.get() != 0) intrusive_ptr_add_ref(r.get());</code>. Postconditions: <code>get() == r.get()</code>. </blockquote> <h3><a name="destructor">destructor</a></h3> <pre>~intrusive_ptr();</pre> <blockquote> Effects: <code>if(get() != 0) intrusive_ptr_release(get());</code>. </blockquote> <h3><a name="assignment">assignment</a></h3> <pre>intrusive_ptr & operator=(intrusive_ptr const & r); template<class Y> intrusive_ptr & operator=(intrusive_ptr<Y> const & r); intrusive_ptr & operator=(T * r);</pre> <blockquote> Effects: Equivalent to <code>intrusive_ptr(r).swap(*this)</code>. Returns: <code>*this</code>. </blockquote> <h3><a name="reset">reset</a></h3> <pre>void reset();</pre> <blockquote> Effects: Equivalent to <code>intrusive_ptr().swap(*this)</code>. </blockquote> <pre>void reset(T * r);</pre> <blockquote> Effects: Equivalent to <code>intrusive_ptr(r).swap(*this)</code>. </blockquote> <pre>void reset(T * r, bool add_ref);</pre> <blockquote> Effects: Equivalent to <code>intrusive_ptr(r, add_ref).swap(*this)</code>. </blockquote> <h3><a name="indirection">indirection</a></h3> <pre>T & operator*() const; // never throws</pre> <blockquote> Requirements: <code>get() != 0</code>. Returns: <code>*get()</code>. Throws: nothing. </blockquote> <pre>T * operator->() const; // never throws</pre> <blockquote> Requirements: <code>get() != 0</code>. Returns: <code>get()</code>. Throws: nothing. </blockquote> <h3><a name="get">get</a></h3> <pre>T * get() const; // never throws</pre> <blockquote> Returns: the stored pointer. Throws: nothing. </blockquote> <h3><a name="detach">detach</a></h3> <pre>T * detach(); // never throws</pre> <blockquote> Returns: the stored pointer. Throws: nothing. Postconditions: <code>get() == 0</code>. Notes: The returned pointer has an elevated reference count. This allows conversion of an <code>intrusive_ptr</code> back to a raw pointer, without the performance overhead of acquiring and dropping an extra reference. It can be viewed as the complement of the non-reference-incrementing constructor. Caution: Using <code>detach</code> escapes the safety of automatic reference counting provided by <code>intrusive_ptr</code>. It should by used only where strictly necessary (such as when interfacing to an existing API), and when the implications are thoroughly understood. </blockquote> <h3><a name="conversions">conversions</a></h3> <pre>operator unspecified-bool-type () const; // never throws</pre> <blockquote> Returns: an unspecified value that, when used in boolean contexts, is equivalent to <code>get() != 0</code>. Throws: nothing. Notes: This conversion operator allows <code>intrusive_ptr</code> objects to be used in boolean contexts, like <code>if (p && p->valid()) {}</code>. The actual target type is typically a pointer to a member function, avoiding many of the implicit conversion pitfalls. </blockquote> <h3><a name="swap">swap</a></h3> <pre>void swap(intrusive_ptr & b); // never throws</pre> <blockquote> Effects: Exchanges the contents of the two smart pointers. Throws: nothing. </blockquote> <h2><a name="functions">Free Functions</a></h2> <h3><a name="comparison">comparison</a></h3> <pre>template<class T, class U> bool operator==(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws</pre> <blockquote> Returns: <code>a.get() == b.get()</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator!=(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws</pre> <blockquote> Returns: <code>a.get() != b.get()</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator==(intrusive_ptr<T> const & a, U * b); // never throws</pre> <blockquote> Returns: <code>a.get() == b</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator!=(intrusive_ptr<T> const & a, U * b); // never throws</pre> <blockquote> Returns: <code>a.get() != b</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator==(T * a, intrusive_ptr const & b); // never throws</pre> <blockquote> Returns: <code>a == b.get()</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator!=(T * a, intrusive_ptr const & b); // never throws</pre> <blockquote> Returns: <code>a != b.get()</code>. Throws: nothing. </blockquote> <pre>template<class T, class U> bool operator<(intrusive_ptr<T> const & a, intrusive_ptr const & b); // never throws</pre> <blockquote> Returns: <code>std::less<T *>()(a.get(), b.get())</code>. Throws: nothing. Notes: Allows <code>intrusive_ptr</code> objects to be used as keys in associative containers. </blockquote> <h3><a name="free-swap">swap</a></h3> <pre>template<class T> void swap(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws</pre> <blockquote> Effects: Equivalent to <code>a.swap(b)</code>. Throws: nothing. Notes: Matches the interface of <code>std::swap</code>. Provided as an aid to generic programming. </blockquote> <h3><a name="get_pointer">get_pointer</a></h3> <pre>template<class T> T * get_pointer(intrusive_ptr<T> const & p); // never throws</pre> <blockquote> Returns: <code>p.get()</code>. Throws: nothing. Notes: Provided as an aid to generic programming. Used by <a href="../bind/mem_fn.html"> mem_fn</a>. </blockquote> <h3><a name="static_pointer_cast">static_pointer_cast</a></h3> <pre>template<class T, class U> intrusive_ptr<T> static_pointer_cast(intrusive_ptr const & r); // never throws</pre> <blockquote> Returns: <code>intrusive_ptr<T>(static_cast<T*>(r.get()))</code>. Throws: nothing. </blockquote> <h3><a name="const_pointer_cast">const_pointer_cast</a></h3> <pre>template<class T, class U> intrusive_ptr<T> const_pointer_cast(intrusive_ptr const & r); // never throws</pre> <blockquote> Returns: <code>intrusive_ptr<T>(const_cast<T*>(r.get()))</code>. Throws: nothing. </blockquote> <h3><a name="dynamic_pointer_cast">dynamic_pointer_cast</a></h3> <pre>template<class T, class U> intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr const & r);</pre> <blockquote> Returns: <code>intrusive_ptr<T>(dynamic_cast<T*>(r.get()))</code>. Throws: nothing. </blockquote> <h3><a name="insertion-operator">operator<<</a></h3> <pre>template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p);</pre> <blockquote> Effects: <code>os << p.get();</code>. Returns: <code>os</code>. </blockquote> <hr> $Date$ Copyright © 2003-2005, 2013 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>. </body> </html>