forked from boostorg/smart_ptr
weak_ptr::expired() added; weak_ptr documentation updated.
[SVN r13141]
This commit is contained in:
Peter Dimov
@ -97,7 +97,7 @@ public:
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T * get() const // never throws; unsafe in multithreaded programs!
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{
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return use_count() == 0? 0: px;
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return pn.use_count() == 0? 0: px;
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}
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long use_count() const // never throws
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@ -105,6 +105,11 @@ public:
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return pn.use_count();
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}
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bool expired() const // never throws
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{
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return pn.use_count() == 0;
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}
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void swap(this_type & other) // never throws
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{
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std::swap(px, other.px);
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@ -297,7 +297,7 @@ q = p;
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<pre>template<typename T>
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bool operator<(shared_ptr<T> const & a, shared_ptr<T> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> an implementation-defined value such that <code>operator<</code>
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<p><b>Returns:</b> an implementation-defined value such that <b>operator<</b>
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is a strict weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code>
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of the C++ standard.</p>
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<p><b>Throws:</b> nothing.</p>
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@ -343,7 +343,7 @@ q = p;
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<LI>
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Otherwise, a default-constructed <STRONG>shared_ptr<T></STRONG> object.</LI></UL>
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<P><B>Throws:</B> <STRONG>std::bad_alloc</STRONG>.</P>
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<P><B>Exception safety:</B> If an exception is thrown, the function has no
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<P><B>Exception safety:</B> If an exception is thrown, the function has no
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effect.</P>
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<P><B>Notes:</B> the seemingly equivalent expression</P>
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<P><CODE>shared_ptr<T>(dynamic_cast<T*>(r.get()))</CODE></P>
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416
weak_ptr.htm
416
weak_ptr.htm
@ -1,35 +1,25 @@
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<title>weak_ptr</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="middle" width="277" height="86">weak_ptr class template</h1>
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<p>The <b>weak_ptr</b> class template stores a pointer to an
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object that's already managed by a <b>shared_ptr</b>. When the
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object last <b>shared_ptr</b> to the object goes away and the object
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is deleted, all <b>weak_ptr</b> objects have their stored pointers
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set to 0.</p>
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<p>Every <b>weak_ptr</b> meets the <b>CopyConstructible</b>
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and <b>Assignable</b> requirements of the C++ Standard Library, and so
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can be used in standard library containers. Comparison operators
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are supplied so that <b>weak_ptr</b> works with
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the standard library's associative containers.</p>
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<p>The class template is parameterized on <b>T</b>, the type of the object
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pointed to. <b>T</b> must meet the smart pointer
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<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
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<h2><a name="Synopsis">Synopsis</a></h2>
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<pre>namespace boost {
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<head>
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<title>weak_ptr</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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</head>
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<body bgcolor="#ffffff" text="#000000">
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<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="middle" width="277" height="86">weak_ptr
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class template</h1>
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<p>The <b>weak_ptr</b> class template stores a pointer to an object that's already
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managed by a <b>shared_ptr</b>. When the object last <b>shared_ptr</b> to the
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object goes away and the object is deleted, all <b>weak_ptr</b> objects have
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their stored pointers set to 0.</p>
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<p>Every <b>weak_ptr</b> meets the <b>CopyConstructible</b> and <b>Assignable</b> requirements
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of the C++ Standard Library, and so can be used in standard library containers.
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Comparison operators are supplied so that <b>weak_ptr</b> works with the
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standard library's associative containers.</p>
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<p>The class template is parameterized on <b>T</b>, the type of the object pointed
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to. <b>T</b> must meet the smart pointer <a href="smart_ptr.htm#Common requirements">
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common requirements</a>.</p>
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<h2><a name="Synopsis">Synopsis</a></h2>
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<pre>namespace boost {
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template<typename T> class weak_ptr {
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@ -48,12 +38,10 @@ pointed to. <b>T</b> must meet the smart pointer
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template<typename Y> weak_ptr & <a href="#assignment">operator=</a>(shared_ptr<Y> const & r); // never throws
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void <a href="#reset">reset</a>();
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T & <a href="#indirection">operator*</a>() const; // never throws
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T * <a href="#indirection">operator-></a>() const; // never throws
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T * <a href="#get">get</a>() const; // never throws
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T * <a href="#get">get</a>() const; // never throws; unsafe in multithreaded code!
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long <a href="#use_count">use_count</a>() const; // never throws
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bool <a href="#expired">expired</a>() const; // never throws
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void <a href="#swap">swap</a>(weak_ptr<T> & b); // never throws
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};
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@ -67,174 +55,218 @@ pointed to. <b>T</b> must meet the smart pointer
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template<typename T> void <a href="#free-swap">swap</a>(weak_ptr<T> & a, weak_ptr<T> & b); // never throws
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template<typename T>
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shared_ptr<T> <a href="#make_shared">make_shared</a>(weak_ptr<T> const & r); // never throws
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template<typename T, typename U>
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weak_ptr<T> <a href="#shared_static_cast">shared_static_cast</a>(weak_ptr<U> const & r); // never throws
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weak_ptr<T> <a href="#shared_static_cast">shared_static_cast</a>(weak_ptr<U> const & r); // never throws
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template<typename T, typename U>
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weak_ptr<T> <a href="#shared_dynamic_cast">shared_dynamic_cast</a>(weak_ptr<U> const & r);
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weak_ptr<T> <a href="#shared_dynamic_cast">shared_dynamic_cast</a>(weak_ptr<U> const & r);
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template<typename T, typename U>
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weak_ptr<T> <a href="#shared_polymorphic_cast">shared_polymorphic_cast</a>(weak_ptr<U> const & r);
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weak_ptr<T> <a href="#shared_polymorphic_cast">shared_polymorphic_cast</a>(weak_ptr<U> const & r);
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template<typename T, typename U>
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weak_ptr<T> <a href="#shared_polymorphic_downcast">shared_polymorphic_downcast</a>(weak_ptr<U> const & r); // never throws
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weak_ptr<T> <a href="#shared_polymorphic_downcast">shared_polymorphic_downcast</a>(weak_ptr<U> const & r); // never throws
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}</pre>
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<h2><a name="Members">Members</a></h2>
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<h3><a name="element_type">element_type</a></h3>
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<pre>typedef T element_type;</pre>
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<p>Provides the type of the stored pointer.</p>
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<h3><a name="constructors">constructors</a></h3>
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<pre>explicit weak_ptr();</pre>
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<p>Constructs a <b>weak_ptr</b>, with 0 as its stored pointer.
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The only exception which may be thrown by this constructor is <b>std::bad_alloc</b>.
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If an exception is thrown, the constructor has no effect.</p>
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<pre>template<typename Y> weak_ptr</a>(shared_ptr<Y> const & r); // never throws</pre>
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<p>Constructs a <b>weak_ptr</b>, as if by storing a copy of the pointer stored in <b>r</b>.
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Afterwards, the <a href="#use_count">use count</a> for all copies is unchanged.
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When the last <b>shared_ptr</b> is destroyed, the use count and stored pointer become 0.</p>
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<pre>weak_ptr(weak_ptr const & r); // never throws
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}
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</pre>
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<h2><a name="Members">Members</a></h2>
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<h3><a name="element_type">element_type</a></h3>
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<pre>typedef T element_type;</pre>
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<blockquote>
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<p>Provides the type of the template parameter T.</p>
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</blockquote>
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<h3><a name="constructors">constructors</a></h3>
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<pre>explicit weak_ptr();</pre>
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<blockquote>
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<p><b>Effects:</b> Constructs a <b>weak_ptr</b>.</p>
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<p><b>Postconditions:</b> <A href="#use_count">use count</A> is 0; the stored
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pointer is 0.</p>
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<p><b>Throws:</b> <b>std::bad_alloc</b>.</p>
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<p><b>Exception safety:</b> If an exception is thrown, the constructor has no
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effect.</p>
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<P><B>Notes:</B> <B>T</B> need not be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
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common requirements</A>.</P>
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</blockquote>
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<pre>template<typename Y> weak_ptr</A>(shared_ptr<Y> const & r); // never throws</pre>
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<blockquote>
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<p><b>Effects:</b> Constructs a <b>weak_ptr</b>, as if by storing a copy of the
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pointer stored in <b>r</b>.</p>
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<p><b>Throws:</b> nothing.</p>
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<P><B>Notes:</B> The <a href="#use_count">use count</a> for all copies is
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unchanged. When the last <b>shared_ptr</b> is destroyed, the use count and
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stored pointer become 0.</P>
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</blockquote>
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<pre>weak_ptr(weak_ptr const & r); // never throws
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template<typename Y> weak_ptr(weak_ptr<Y> const & r); // never throws</pre>
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<p>Constructs a <b>weak_ptr</b>, as if by storing a copy of the
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pointer stored in <b>r</b>.</p>
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<h3><a name="destructor">destructor</a></h3>
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<pre>~weak_ptr(); // never throws</pre>
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<p>Destroys this <b>weak_ptr</b> but has no effect on the object its stored pointer points to.
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<b>T</b> need not be a complete type.
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See the smart pointer <a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
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<h3><a name="operator=">assignment</a></h3>
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<pre>weak_ptr & <a href="#assignment">operator=</a>(weak_ptr const & r); // never throws
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<blockquote>
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<p><b>Effects:</b> Constructs a <b>weak_ptr</b>, as if by storing a copy of the
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pointer stored in <b>r</b>.</p>
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<p><b>Throws:</b> nothing.</p>
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<P><B>Notes:</B> The <a href="#use_count">use count</a> for all copies is
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unchanged.</P>
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</blockquote>
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<h3><a name="destructor">destructor</a></h3>
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<pre>~weak_ptr(); // never throws</pre>
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<BLOCKQUOTE>
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<P><B>Effects:</B> Destroys this <b>weak_ptr</b> but has no effect on the object
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its stored pointer points to.</P>
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<P><B>Throws:</B> nothing.</P>
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<P><B>Notes:</B> <B>T</B> need not be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
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common requirements</A>.</P>
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</BLOCKQUOTE>
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<h3><a name="assignment">assignment</a></h3>
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<pre>weak_ptr & <a href="#assignment">operator=</a>(weak_ptr const & r); // never throws
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template<typename Y> weak_ptr & <a href="#assignment">operator=</a>(weak_ptr<Y> const & r); // never throws
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template<typename Y> weak_ptr & <a href="#assignment">operator=</a>(shared_ptr<Y> const & r); // never throws</pre>
|
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<p>Constructs a new <b>weak_ptr</b> as described <a href="#constructors">above</a>,
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then replaces this <b>weak_ptr</b> with the new one, destroying the replaced object.</p>
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<h3><a name="reset">reset</a></h3>
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<pre>void reset();</pre>
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<p>Constructs a new <b>weak_ptr</b> as described <a href="#constructors">above</a>,
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then replaces this <b>weak_ptr</b> with the new one, destroying the replaced object.
|
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The only exception which may be thrown is <b>std::bad_alloc</b>. If
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an exception is thrown, the <b>reset</b> has no effect.</p>
|
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|
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<h3><a name="indirection">indirection</a></h3>
|
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|
||||
<pre>T & operator*() const; // never throws</pre>
|
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<p>Returns a reference to the object pointed to by the stored pointer.
|
||||
Behavior is undefined if the stored pointer is 0.
|
||||
Note that the stored pointer becomes 0 if all <b>shared_ptr</b> objects for that
|
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pointer are destroyed.</p>
|
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|
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<pre>T * operator->() const; // never throws</pre>
|
||||
<p>Returns the stored pointer.
|
||||
Behavior is undefined if the stored pointer is 0.
|
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Note that the stored pointer becomes 0 if all <b>shared_ptr</b> objects for that
|
||||
pointer are destroyed.</p>
|
||||
|
||||
<h3><a name="get">get</a></h3>
|
||||
<pre>T * get() const; // never throws</pre>
|
||||
<p>Returns the stored pointer.
|
||||
Note that the stored pointer becomes 0 if all <b>shared_ptr</b> objects for that
|
||||
pointer are destroyed.
|
||||
<b>T</b> need not be a complete type.
|
||||
See the smart pointer
|
||||
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
|
||||
|
||||
<h3><a name="use_count">use_count</a></h3>
|
||||
<pre>long use_count() const; // never throws</pre>
|
||||
<p>Returns the number of <b>shared_ptr</b> objects sharing ownership of the
|
||||
stored pointer.
|
||||
<b>T</b> need not be a complete type.
|
||||
See the smart pointer
|
||||
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
|
||||
<p>Because <b>use_count</b> is not necessarily efficient to implement for
|
||||
implementations of <b>weak_ptr</b> that do not use an explicit reference
|
||||
count, it might be removed from some future version. Thus it should
|
||||
be used for debugging purposes only, and <b>get</b> should be used for
|
||||
production code.</p>
|
||||
|
||||
<h3><a name="swap">swap</a></h3>
|
||||
<pre>void swap(weak_ptr & b); // never throws</pre>
|
||||
<p>Exchanges the contents of the two smart pointers.
|
||||
<b>T</b> need not be a complete type.
|
||||
See the smart pointer
|
||||
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
|
||||
|
||||
<h2><a name="functions">Free Functions</a></h2>
|
||||
|
||||
<h3><a name="comparison">comparison</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
<BLOCKQUOTE>
|
||||
<P><B>Effects:</B> Equivalent to <code>weak_ptr(r).swap(*this)</code>.</P>
|
||||
<P><B>Throws:</B> nothing.</P>
|
||||
<P><B>Notes:</B> The implementation is free to meet the effects (and the implied
|
||||
guarantees) via different means, without creating a temporary.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="reset">reset</a></h3>
|
||||
<pre>void reset();</pre>
|
||||
<BLOCKQUOTE>
|
||||
<P><B>Effects:</B> Equivalent to <code>weak_ptr().swap(*this)</code>.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="get">get</a></h3>
|
||||
<pre>T * get() const; // never throws</pre>
|
||||
<blockquote>
|
||||
<p><b>Returns:</b> the stored pointer (0 if all <b>shared_ptr</b> objects for that
|
||||
pointer are destroyed.)</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> Using <b>get</b> in multithreaded code is dangerous. After the
|
||||
function returns, the pointed-to object may be destroyed by a different thread,
|
||||
since the <b>weak_ptr</b> doesn't affect its <b>use_count</b>.</P>
|
||||
</blockquote>
|
||||
<h3><a name="use_count">use_count</a></h3>
|
||||
<pre>long use_count() const; // never throws</pre>
|
||||
<blockquote>
|
||||
<p><b>Returns:</b> the number of <b>shared_ptr</b> objects sharing ownership of the
|
||||
stored pointer.</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> <code>use_count()</code> is not necessarily efficient. Use only
|
||||
for debugging and testing purposes, not for production code. <B>T</B> need not
|
||||
be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
|
||||
common requirements</A>.</P>
|
||||
</blockquote>
|
||||
<h3><a name="expired">expired</a></h3>
|
||||
<pre>bool expired() const; // never throws</pre>
|
||||
<blockquote>
|
||||
<p><b>Returns:</b> <code>use_count() == 0</code>.</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> <code>expired()</code> may be faster than <code>use_count()</code>.
|
||||
<B>T</B> need not be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
|
||||
common requirements</A>.</P>
|
||||
</blockquote>
|
||||
<h3><a name="swap">swap</a></h3>
|
||||
<pre>void swap(weak_ptr & b); // never throws</pre>
|
||||
<blockquote>
|
||||
<p><b>Effects:</b> Exchanges the contents of the two smart pointers.</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> <B>T</B> need not be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
|
||||
common requirements</A>.</P>
|
||||
</blockquote>
|
||||
<h2><a name="functions">Free Functions</a></h2>
|
||||
<h3><a name="comparison">comparison</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
bool operator==(weak_ptr<T> const & a, weak_ptr<U> const & b); // never throws
|
||||
template<typename T, typename U>
|
||||
bool operator!=(weak_ptr<T> const & a, weak_ptr<U> const & b); // never throws
|
||||
template<typename T>
|
||||
bool operator!=(weak_ptr<T> const & a, weak_ptr<U> const & b); // never throws</pre>
|
||||
<blockquote>
|
||||
<p><b>Returns:</b> <code>a.get() == b.get()</code>.</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> <B>T</B> need not be a complete type. See the smart pointer <A href="smart_ptr.htm#Common requirements">
|
||||
common requirements</A>.</P>
|
||||
</blockquote>
|
||||
<pre>template<typename T>
|
||||
bool operator<(weak_ptr<T> const & a, weak_ptr<T> const & b); // never throws</pre>
|
||||
<p>Compares the stored pointers of the two smart pointers.
|
||||
<b>T</b> need not be a complete type.
|
||||
See the smart pointer
|
||||
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
|
||||
<p>The <b>operator<</b> overload is provided to define an ordering so that <b>weak_ptr</b>
|
||||
objects can be used in associative containers such as <b>std::map</b>.
|
||||
The implementation uses <b>std::less<T *></b> to perform the
|
||||
comparison. This ensures that the comparison is handled correctly, since the
|
||||
standard mandates that relational operations on pointers are unspecified (5.9 [expr.rel]
|
||||
paragraph 2) but <b>std::less<></b> on pointers is well-defined (20.3.3 [lib.comparisons]
|
||||
paragraph 8).</p>
|
||||
|
||||
<h3><a name="free-swap">swap</a></h3>
|
||||
<pre>template<typename T>
|
||||
<blockquote>
|
||||
<p><b>Returns:</b> an implementation-defined value such that <b>operator<</b> is
|
||||
a strict weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code>
|
||||
of the C++ standard.</p>
|
||||
<p><b>Throws:</b> nothing.</p>
|
||||
<P><B>Notes:</B> Allows <STRONG>weak_ptr</STRONG> objects to be used as keys in
|
||||
associative containers. <B>T</B> need not be a complete type. See the smart
|
||||
pointer <A href="smart_ptr.htm#Common requirements">common requirements</A>.</P>
|
||||
</blockquote>
|
||||
<h3><a name="free-swap">swap</a></h3>
|
||||
<pre>template<typename T>
|
||||
void swap(weak_ptr<T> & a, weak_ptr<T> & b) // never throws</pre>
|
||||
<p>Equivalent to <b>a.swap(b)</b>. Matches the interface of <b>std::swap</b>.
|
||||
Provided as an aid to generic programming.</p>
|
||||
|
||||
<h3><a name="shared_static_cast">shared_static_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_static_cast(weak_ptr<U> const & r); // never throws</pre>
|
||||
<p>Perform a <b>static_cast</b> on the stored pointer, returning another <b>weak_ptr</b>.
|
||||
The resulting smart pointer will share its use count with the original pointer.</p>
|
||||
|
||||
<h3><a name="shared_dynamic_cast">shared_dynamic_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_dynamic_cast(weak_ptr<U> const & r);</pre>
|
||||
<p>Perform a <b>dynamic_cast</b> on the stored pointer, returning another <b>weak_ptr</b>.
|
||||
The resulting smart pointer will share its use count with the original pointer unless the result of the
|
||||
cast is 0. The only exception which may be thrown is <b>std::bad_alloc</b>, which may be thrown during the
|
||||
construction of the new <b>weak_ptr</b> if the result of the cast is 0. If an exception is thrown, the
|
||||
cast has no effect.</p>
|
||||
|
||||
<h3><a name="shared_polymorphic_cast">shared_polymorphic_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_polymorphic_cast(weak_ptr<U> const & r);</pre>
|
||||
<p>Perform a <a href="../conversion/cast.htm#Polymorphic_cast"><b>polymorphic_cast</b><a> on the stored pointer,
|
||||
returning another <b>weak_ptr</b>.
|
||||
The resulting smart pointer will share its use count with the original pointer.
|
||||
The only exception which may be thrown is <b>std::bad_cast</b>, if the pointer type can not be converted.
|
||||
If an exception is thrown, the cast has no effect.</p>
|
||||
|
||||
<h3><a name="shared_polymorphic_downcast">shared_polymorphic_downcast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_polymorphic_downcast(weak_ptr<U> const & r); // never throws</pre>
|
||||
<p>Perform a <a href="../conversion/cast.htm#Polymorphic_cast"><b>polymorphic_downcast</b><a> on the stored pointer,
|
||||
returning another <b>weak_ptr</b>.
|
||||
The resulting smart pointer will share its use count with the original pointer.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan -->8 February 2002<!--webbot bot="Timestamp" i-checksum="38439" endspan --></p>
|
||||
|
||||
<p>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler.
|
||||
Permission to copy, use, modify, sell and distribute this document is granted
|
||||
provided this copyright notice appears in all copies.
|
||||
This document is provided "as is" without express or implied warranty,
|
||||
and with no claim as to its suitability for any purpose.</p>
|
||||
|
||||
</body>
|
||||
|
||||
<BLOCKQUOTE>
|
||||
<P><B>Effects:</B> Equivalent to <code>a.swap(b)</code>.</P>
|
||||
<P><B>Throws:</B> nothing.</P>
|
||||
<P><B>Notes:</B> Matches the interface of <B>std::swap</B>. Provided as an aid to
|
||||
generic programming.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="make_shared">make_shared</a></h3>
|
||||
<pre>template<typename T>
|
||||
shared_ptr<T> make_shared(weak_ptr<T> & const r) // never throws</pre>
|
||||
<BLOCKQUOTE>
|
||||
<P><B>Returns:</B> <code>r.expired()? shared_ptr<T>(): shared_ptr<T>(r)</code>.</P>
|
||||
<P><B>Throws:</B> nothing.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="shared_static_cast">shared_static_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_static_cast(weak_ptr<U> const & r); // never throws</pre>
|
||||
<BLOCKQUOTE>
|
||||
<P><STRONG>Requires:</STRONG> The expression <code>static_cast<T*>(r.get())</code>
|
||||
must be well-formed.</P>
|
||||
<P><B>Returns:</B> A <STRONG>weak_ptr<T></STRONG> object that stores a copy
|
||||
of <code>static_cast<T*>(r.get())</code> and shares ownership with <b>r</b>.</P>
|
||||
<P><B>Throws:</B> nothing.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="shared_dynamic_cast">shared_dynamic_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_dynamic_cast(weak_ptr<U> const & r);</pre>
|
||||
<BLOCKQUOTE>
|
||||
<P><STRONG>Requires:</STRONG> The expression <CODE>dynamic_cast<T*>(r.get())</CODE>
|
||||
must be well-formed and its behavior defined.</P>
|
||||
<P><B>Returns:</B></P>
|
||||
<UL>
|
||||
<LI>
|
||||
When <CODE>dynamic_cast<T*>(r.get())</CODE> returns a nonzero
|
||||
value, a <STRONG>weak_ptr<T></STRONG> object that stores a copy of
|
||||
it and shares ownership with <STRONG>r</STRONG>;
|
||||
<LI>
|
||||
Otherwise, a default-constructed <STRONG>weak_ptr<T></STRONG> object.</LI></UL>
|
||||
<P><B>Throws:</B> <STRONG>std::bad_alloc</STRONG>.</P>
|
||||
<P><B>Exception safety:</B> If an exception is thrown, the function has no effect.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="shared_polymorphic_cast">shared_polymorphic_cast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_polymorphic_cast(weak_ptr<U> const & r);</pre>
|
||||
<BLOCKQUOTE>
|
||||
<p><STRONG>Requires:</STRONG> The expression <CODE><A href="../conversion/cast.htm#Polymorphic_cast">
|
||||
polymorphic_cast</A><T*>(r.get())</CODE> must be well-formed and
|
||||
its behavior defined.</p>
|
||||
<P><B>Returns:</B> A <STRONG>weak_ptr<T></STRONG> object that stores a copy
|
||||
of <CODE><A href="../conversion/cast.htm#Polymorphic_cast">polymorphic_cast</A><T*>(r.get())</CODE>
|
||||
and shares ownership with <B>r</B>.</P>
|
||||
<P><B>Throws:</B> <STRONG>std::bad_cast</STRONG> when the pointer cannot be
|
||||
converted.</P>
|
||||
<P><B>Exception safety:</B> If an exception is thrown, the function has no effect.</P>
|
||||
</BLOCKQUOTE>
|
||||
<h3><a name="shared_polymorphic_downcast">shared_polymorphic_downcast</a></h3>
|
||||
<pre>template<typename T, typename U>
|
||||
weak_ptr<T> shared_polymorphic_downcast(weak_ptr<U> const & r); // never throws</pre>
|
||||
<BLOCKQUOTE>
|
||||
<p><STRONG>Requires:</STRONG> The expression <CODE><A href="../conversion/cast.htm#Polymorphic_cast">
|
||||
polymorphic_downcast</A><T*>(r.get())</CODE> must be well-formed
|
||||
and its behavior defined.</p>
|
||||
<P><B>Returns:</B> A <STRONG>weak_ptr<T></STRONG> object that stores a copy
|
||||
of <CODE><A href="../conversion/cast.htm#Polymorphic_cast">polymorphic_downcast</A><T*>(r.get())</CODE>
|
||||
and shares ownership with <B>r</B>.</P>
|
||||
<P><B>Throws:</B> nothing.</P>
|
||||
</BLOCKQUOTE>
|
||||
<hr>
|
||||
<p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan -->
|
||||
8 March 2002<!--webbot bot="Timestamp" i-checksum="38439" endspan --></p>
|
||||
<p>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler.
|
||||
Copyright 2002 Peter Dimov. Permission to copy, use, modify, sell and
|
||||
distribute this document is granted provided this copyright notice appears in
|
||||
all copies. This document is provided "as is" without express or implied
|
||||
warranty, and with no claim as to its suitability for any purpose.</p>
|
||||
</A>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
Reference in New Issue
Block a user