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extern/stdcxx/4.2.1/doc/stdlibref/auto-ptr.html
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extern/stdcxx/4.2.1/doc/stdlibref/auto-ptr.html
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<HTML>
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<HEAD>
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<TITLE>auto_ptr</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="associativecontainers.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="back-insert-iterator.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>auto_ptr</H2>
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<P><B>Library:</B> <A HREF="2-4.html">General utilities</A></P>
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<PRE><HR><B><I>Does not inherit</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Interface</A></LI>
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<LI><A HREF="#sec6">Struct auto_ptr_ref</A></LI>
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<LI><A HREF="#sec7">Typedef</A></LI>
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<LI><A HREF="#sec8">Constructors</A></LI>
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<LI><A HREF="#sec9">Destructors</A></LI>
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<LI><A HREF="#sec10">Operators</A></LI>
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<LI><A HREF="#sec11">Member Functions</A></LI>
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<LI><A HREF="#sec12">Example</A></LI>
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<LI><A HREF="#sec13">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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<H4>Members</H4>
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<UL><TABLE CELLPADDING=3>
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<TR><TD VALIGN=top>
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<A HREF="#idx21">auto_ptr()</A><BR>
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<A HREF="#idx19">auto_ptr_ref</A><BR>
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<A HREF="#idx20">element_type</A><BR>
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</TD>
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<TD VALIGN=top><A HREF="#idx30">get()</A><BR>
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<A HREF="#idx29">operator auto_ptr<Y>()</A><BR>
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<A HREF="#idx28">operator auto_ptr_ref<Y>()</A><BR>
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</TD>
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<TD VALIGN=top><A HREF="#idx26">operator*()</A><BR>
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<A HREF="#idx27">operator->()</A><BR>
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<A HREF="#idx25">operator=()</A><BR>
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</TD>
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<TD VALIGN=top><A HREF="#idx31">release()</A><BR>
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<A HREF="#idx32">reset()</A><BR>
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<A HREF="#idx24">~auto_ptr()</A><BR>
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</TD></TR>
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</TABLE></UL>
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>A simple smart pointer class</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <memory>
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namespace std {
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template <class X> class auto_ptr;
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>The class template specialization <B><I>auto_ptr</I></B> holds onto a pointer obtained via <SAMP>new()</SAMP> and then deletes that object when the <B><I>auto_ptr</I></B> object itself is destroyed. <B><I>auto_ptr</I></B> can be used to make calls to operator <SAMP>new()</SAMP> exception-safe. The <B><I>auto_ptr</I></B> class has semantics of strict ownership: an object may be safely pointed to by only one <B><I>auto_ptr</I></B>, so copying an <B><I>auto_ptr</I></B> copies the pointer and transfers ownership to the destination if the source had already had ownership. </P>
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<A NAME="sec5"><H3>Interface</H3></A>
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<UL><PRE>namespace std {
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template <class Y> struct auto_ptr_ref {};
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template <class X> class auto_ptr {
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public:
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typedef X element_type;
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// construct/copy/destroy
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explicit auto_ptr (X* p = 0) throw();
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auto_ptr(auto_ptr<X>&) throw ();
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template <class Y>
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auto_ptr(auto_ptr<Y>&) throw();
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auto_ptr<X>& operator=(auto_ptr<X>&) throw();
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template <class Y>
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auto_ptr<X>& operator= (auto_ptr<Y>&) throw();
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~auto_ptr() throw();
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// members
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X& operator* () const throw();
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X* operator-> () const throw();
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X* get () const throw();
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X* release() throw();
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void reset(X* p = 0) throw();
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// conversions
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auto_ptr(auto_ptr_ref<X>) throw();
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template <class Y> operator auto_ptr_ref<Y>() throw();
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template <class Y> operator auto_ptr<Y>() throw();
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};
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}
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</PRE></UL>
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<A NAME="sec6"><H3>Struct auto_ptr_ref</H3></A>
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<A NAME="idx19"></A><PRE>template <class Y>
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struct <B>auto_ptr_ref</B>;</PRE>
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<UL>
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<P>A namespace-scope struct template that holds a reference to an <B><I>auto_ptr</I></B>. An <B><I>auto_ptr_ref</I></B> can only be constructed within an <B><I>auto_ptr</I></B> using a reference to an <B><I>auto_ptr</I></B>. It prevents unsafe copying.</P>
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</UL>
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<A NAME="sec7"><H3>Typedef</H3></A>
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<A NAME="idx20"></A><PRE>typedef X <B>element_type</B>;</PRE>
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<UL>
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<P>The type of element pointed to by <B><I>auto_ptr</I></B>. </P>
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</UL>
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<A NAME="sec8"><H3>Constructors</H3></A>
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<A NAME="idx21"></A><PRE>explicit
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<B>auto_ptr</B> (X* p = 0) throw();</PRE>
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<UL>
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<P>Constructs an object of class <B><I>auto_ptr<X></I></B>, initializing the held pointer to <SAMP>p</SAMP>, and acquiring ownership of that pointer. <SAMP>p</SAMP> must point to an object of class <SAMP>X</SAMP>, a class derived from <SAMP>X</SAMP> for which <SAMP>delete p</SAMP> is defined and accessible, or <SAMP>p</SAMP> must be a null pointer.</P>
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</UL>
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<A NAME="idx22"></A><PRE><B>auto_ptr</B> (auto_ptr<X>& a) throw();
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template <class Y>
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<B>auto_ptr</B> (auto_ptr<Y>& a) throw();</PRE>
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<UL>
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<P>Constructs an object of class <B><I>auto_ptr<X></I></B>, and copies the argument <SAMP>a</SAMP> to <SAMP>*this</SAMP>. If <SAMP>a</SAMP> owned the underlying pointer, then <SAMP>*this</SAMP> becomes the new owner of that pointer.</P>
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<P>For the constructor template, each specialization requires that a pointer to <SAMP>Y</SAMP> be implicitly convertible to pointer to <SAMP>element_type</SAMP>.</P>
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</UL>
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<A NAME="idx23"></A><PRE><B>auto_ptr</B> (auto_ptr_ref<X> r) throw();</PRE>
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<UL>
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<P>Constructs an <B><I>auto_ptr</I></B> from an <B><I>auto_ptr_ref</I></B>.</P>
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</UL>
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<A NAME="sec9"><H3>Destructors</H3></A>
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<A NAME="idx24"></A><PRE><B>~auto_ptr</B> () throw();</PRE>
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<UL>
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<P>Deletes the underlying pointer.</P>
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</UL>
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<A NAME="sec10"><H3>Operators</H3></A>
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<A NAME="idx25"></A><PRE>auto_ptr<X>& <B>operator=</B>(auto_ptr<X>& a) throw();
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template <class Y>
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auto_ptr<X>& <B>operator=</B>(auto_ptr<Y>& a) throw();</PRE>
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<UL>
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<P>Copies the argument <SAMP>a</SAMP> to <SAMP>*this</SAMP>. If <SAMP>a</SAMP> owned the underlying pointer, then <SAMP>*this</SAMP> becomes the new owner of that pointer. If <SAMP>*this</SAMP> already owned a pointer, that pointer is deleted first. The argument <SAMP>a</SAMP> is reset to zero.</P>
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<P>For the function template, each specialization requires that a pointer to <SAMP>Y</SAMP> be implicitly convertible to pointer to <SAMP>element_type</SAMP>.</P>
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</UL>
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<A NAME="idx26"></A><PRE>X&
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<B>operator*</B>() const throw();</PRE>
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<UL>
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<P>Returns a reference to the object to which the underlying pointer points.</P>
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</UL>
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<A NAME="idx27"></A><PRE>X*
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<B>operator-></B>() const throw();</PRE>
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<UL>
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<P>Returns the underlying pointer.</P>
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</UL>
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<A NAME="idx28"></A><PRE>template <class Y>
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<B>operator auto_ptr_ref<Y></B>() throw();</PRE>
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<UL>
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<P>Constructs an <B><I>auto_ptr_ref</I></B> from <SAMP>*this</SAMP> and returns it.</P>
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</UL>
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<A NAME="idx29"></A><PRE>template <class Y>
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<B>operator auto_ptr<Y></B>() throw();</PRE>
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<UL>
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<P>Constructs a new <B><I>auto_ptr</I></B> using the underlying pointer held by <SAMP>*this</SAMP>. Calls <SAMP>release()</SAMP> on <SAMP>*this</SAMP>, so <SAMP>*this</SAMP> no longer possesses the pointer. Returns the new <B><I>auto_ptr</I></B>.</P>
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</UL>
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<A NAME="sec11"><H3>Member Functions</H3></A>
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<A NAME="idx30"></A><PRE>X*
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<B>get</B>() const throw();</PRE>
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<UL>
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<P>Returns the underlying pointer.</P>
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</UL>
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<A NAME="idx31"></A><PRE>X*
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<B>release</B>() throw();</PRE>
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<UL>
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<P>Releases ownership of the underlying pointer and returns that pointer. The <SAMP>*this</SAMP> object is left holding a null pointer.</P>
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</UL>
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<A NAME="idx32"></A><PRE>void
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<B>reset</B>(X* p = 0) throw();</PRE>
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<UL>
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<P>Sets the underlying pointer to <SAMP>p</SAMP>. If non-null, deletes the old underlying pointer.</P>
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</UL>
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<A NAME="sec12"><H3>Example</H3></A>
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<UL><PRE>//
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// auto_ptr.cpp
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//
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#include <iostream> // for cout, endl
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#include <memory> // for auto_ptr
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// A simple structure.
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class X
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{
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int i_;
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public:
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X (int i) : i_ (i) {
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std::cout << "X::X (" << i_ << ')' << std::endl;
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}
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~X () {
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std::cout << "X::~X [" << i_ << ']' << std::endl;
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}
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int get () const { return i_; }
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};
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int main ()
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{
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// a implicitly initialized to 0 (the null pointer)
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std::auto_ptr<X> a;
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// Establish a scope.
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if (1) {
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// b will hold a pointer to an X.
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std::auto_ptr<X> b (new X (12345));
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// a will now be the owner of
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// the underlying pointer.
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a = b;
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}
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std::cout << "b destroyed" << std::endl;
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// Output the value contained by
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// the underlying pointer.
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#ifndef _RWSTD_NO_NONCLASS_ARROW_RETURN
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std::cout << a->get () << std::endl;
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#else
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std::cout << (*a).get () << std::endl;
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#endif
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// The pointer will be deleted when a is destroyed
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// on leaving scope.
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return 0;
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}
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Program Output:
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</PRE></UL>
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<P>X::X (12345)</P>
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<P>b destroyed</P>
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<P>12345</P>
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<P>X::~X [12345]</P>
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<A NAME="sec13"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.4.5</I></P>
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<BR>
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