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    <STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> typename_<STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>=</STRONG> 0<STRONG>;</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>=</STRONG> 0<STRONG>;</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Base<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>

public:
    <STRONG>static</STRONG> <STRONG>int</STRONG> count<STRONG>;</STRONG>

protected:
    Base<STRONG>(</STRONG><STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>)</STRONG><STRONG>;</STRONG>
    Base<STRONG>(</STRONG><STRONG>const</STRONG> Base<STRONG>&amp;</STRONG> base<STRONG>)</STRONG><STRONG>;</STRONG>

private:
    <STRONG>char</STRONG><STRONG>*</STRONG> typename_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

Base::Base<STRONG>(</STRONG><STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> tname <STRONG>=</STRONG> <STRONG>(</STRONG>typename<STRONG>)</STRONG> <STRONG>?</STRONG> typename <STRONG>:</STRONG> &quot;<EM>unknown</EM>&quot;<STRONG>;</STRONG>
    strcpy<STRONG>(</STRONG>typename_ <STRONG>=</STRONG> <STRONG>new</STRONG> <STRONG>char</STRONG><STRONG>[</STRONG>strlen<STRONG>(</STRONG>tname<STRONG>)</STRONG> <STRONG>+</STRONG> 1<STRONG>]</STRONG><STRONG>,</STRONG> tname<STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>++</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

Base::Base<STRONG>(</STRONG><STRONG>const</STRONG> Base<STRONG>&amp;</STRONG> base<STRONG>)</STRONG> <STRONG>{</STRONG>
    strcpy<STRONG>(</STRONG>
        typename_ <STRONG>=</STRONG> <STRONG>new</STRONG> <STRONG>char</STRONG><STRONG>[</STRONG>strlen<STRONG>(</STRONG>base<STRONG>.</STRONG>typename_<STRONG>)</STRONG> <STRONG>+</STRONG> 1<STRONG>]</STRONG><STRONG>,</STRONG> base<STRONG>.</STRONG>typename_
    <STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>++</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

Base::~Base<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>delete</STRONG><STRONG>[</STRONG><STRONG>]</STRONG> typename_<STRONG>;</STRONG>
    <STRONG>--</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> First derived class. </EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> Derived1 <STRONG>:</STRONG> <STRONG>public</STRONG> Base <STRONG>{</STRONG>
public:
    Derived1<STRONG>(</STRONG><STRONG>int</STRONG> data<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived1</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>data<STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    Derived1<STRONG>(</STRONG><STRONG>const</STRONG> Derived1<STRONG>&amp;</STRONG> d<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived1</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>d<STRONG>.</STRONG>data<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Derived1<STRONG>(</STRONG><STRONG>)</STRONG>        <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> <STRONG>new</STRONG> Derived1<STRONG>(</STRONG><STRONG>*</STRONG><STRONG>this</STRONG><STRONG>)</STRONG><STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG><STRONG>;</STRONG>
    <STRONG>int</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> data_<STRONG>;</STRONG> <STRONG>}</STRONG>
private:
    <STRONG>int</STRONG> data_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

<STRONG>virtual</STRONG> <STRONG>void</STRONG> Derived1::identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG>
    os <STRONG>&lt;&lt;</STRONG> &quot;<EM>(</EM>&quot; <STRONG>&lt;&lt;</STRONG> typename<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM> </EM>&quot; <STRONG>&lt;&lt;</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM>)</EM>&quot;<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> Second derived class. </EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> Derived2 <STRONG>:</STRONG> <STRONG>public</STRONG> Base <STRONG>{</STRONG>
public:
    Derived2<STRONG>(</STRONG><STRONG>int</STRONG> data<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived2</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>data<STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    Derived2<STRONG>(</STRONG><STRONG>const</STRONG> Derived2<STRONG>&amp;</STRONG> d<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived2</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>d<STRONG>.</STRONG>data<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Derived2<STRONG>(</STRONG><STRONG>)</STRONG>        <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> <STRONG>new</STRONG> Derived2<STRONG>(</STRONG><STRONG>*</STRONG><STRONG>this</STRONG><STRONG>)</STRONG><STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG><STRONG>;</STRONG>
    <STRONG>int</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> data_<STRONG>;</STRONG> <STRONG>}</STRONG>
private:
    <STRONG>int</STRONG> data_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

<STRONG>virtual</STRONG> <STRONG>void</STRONG> Derived2::identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG>
    os <STRONG>&lt;&lt;</STRONG> &quot;<EM>(</EM>&quot; <STRONG>&lt;&lt;</STRONG> typename<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM> </EM>&quot; <STRONG>&lt;&lt;</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM>)</EM>&quot;<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> now define the pointer wrapper.</EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> BaseWrapper <STRONG>{</STRONG>
public:
    BaseWrapper<STRONG>(</STRONG>Base<STRONG>*</STRONG> base_ptr <STRONG>=</STRONG> 0<STRONG>)</STRONG> <STRONG>:</STRONG> base_ptr_<STRONG>(</STRONG>base_ptr<STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    BaseWrapper<STRONG>(</STRONG><STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> bw<STRONG>)</STRONG> <STRONG>{</STRONG>
        base_ptr_ <STRONG>=</STRONG> bw<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>?</STRONG> bw<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>-&gt;</STRONG>clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>:</STRONG> 0<STRONG>;</STRONG>
    <STRONG>}</STRONG>
    <STRONG>~</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>delete</STRONG> base_ptr_<STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>const</STRONG> Base<STRONG>*</STRONG> <STRONG>operator</STRONG><STRONG>(</STRONG><STRONG>)</STRONG><STRONG>(</STRONG><STRONG>)</STRONG>  <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> base_ptr_<STRONG>;</STRONG> <STRONG>}</STRONG>
    Base<STRONG>*</STRONG> <STRONG>operator</STRONG><STRONG>(</STRONG><STRONG>)</STRONG><STRONG>(</STRONG><STRONG>)</STRONG>  <STRONG>{</STRONG> <STRONG>return</STRONG> base_ptr_<STRONG>;</STRONG> <STRONG>}</STRONG>
    BaseWrapper<STRONG>&amp;</STRONG> <STRONG>operator</STRONG><STRONG>=</STRONG> <STRONG>(</STRONG><STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> bw<STRONG>)</STRONG> <STRONG>{</STRONG>
        <STRONG>delete</STRONG> base_ptr_<STRONG>;</STRONG>
        base_ptr_ <STRONG>=</STRONG> bw<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>-&gt;</STRONG>clone<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>}</STRONG>
private:
    Base<STRONG>*</STRONG> base_ptr_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

bool <STRONG>operator</STRONG><STRONG>==</STRONG> <STRONG>(</STRONG><STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> bw1<STRONG>,</STRONG> <STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> w2<STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>return</STRONG> false<STRONG>;</STRONG>
<STRONG>}</STRONG>

bool <STRONG>operator</STRONG><STRONG>&lt;</STRONG> <STRONG>(</STRONG><STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> bw1<STRONG>,</STRONG> <STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> w2<STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>return</STRONG> false<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> end of class defs.</EM>
<EM><STRONG>//</STRONG></EM>

<EM><STRONG>//</STRONG> define static members.</EM>
<STRONG>int</STRONG> Base::count <STRONG>=</STRONG> 0<STRONG>;</STRONG>

<STRONG>int</STRONG> main<STRONG>(</STRONG><STRONG>int</STRONG><STRONG>,</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG><STRONG>[</STRONG><STRONG>]</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG>
    list<STRONG>&lt;</STRONG>BaseWrapper<STRONG>&gt;</STRONG> list1<STRONG>;</STRONG>
    list1<STRONG>.</STRONG>push_back<STRONG>(</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>new</STRONG> Derived1<STRONG>(</STRONG>101<STRONG>)</STRONG><STRONG>)</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    list1<STRONG>.</STRONG>push_back<STRONG>(</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>new</STRONG> Derived2<STRONG>(</STRONG>201<STRONG>)</STRONG><STRONG>)</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    list1<STRONG>.</STRONG>push_back<STRONG>(</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>new</STRONG> Derived2<STRONG>(</STRONG>202<STRONG>)</STRONG><STRONG>)</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    list1<STRONG>.</STRONG>push_back<STRONG>(</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>new</STRONG> Derived1<STRONG>(</STRONG>102<STRONG>)</STRONG><STRONG>)</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    list1<STRONG>.</STRONG>push_back<STRONG>(</STRONG>BaseWrapper<STRONG>(</STRONG><STRONG>new</STRONG> Derived2<STRONG>(</STRONG>203<STRONG>)</STRONG><STRONG>)</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>

    list<STRONG>&lt;</STRONG>BaseWrapper<STRONG>&gt;</STRONG><STRONG>::</STRONG>const_iterator it <STRONG>=</STRONG> list1<STRONG>.</STRONG>begin<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>for</STRONG><STRONG>(</STRONG><STRONG>;</STRONG> it <STRONG>!=</STRONG> list1<STRONG>.</STRONG>end<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>;</STRONG> <STRONG>++</STRONG>it<STRONG>)</STRONG> <STRONG>{</STRONG>
        <STRONG>const</STRONG> BaseWrapper<STRONG>&amp;</STRONG> bw <STRONG>=</STRONG> <STRONG>*</STRONG>it<STRONG>;</STRONG>
        bw<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>-&gt;</STRONG>identify<STRONG>(</STRONG>cerr<STRONG>)</STRONG><STRONG>;</STRONG> 
        cerr <STRONG>&lt;&lt;</STRONG> &quot;<EM> </EM>&quot;<STRONG>;</STRONG>
    <STRONG>}</STRONG>
    cerr <STRONG>&lt;&lt;</STRONG> endl <STRONG>&lt;&lt;</STRONG> endl<STRONG>;</STRONG>

    <STRONG>return</STRONG> 0<STRONG>;</STRONG>
<STRONG>}</STRONG>

</PRE>
<hr>
And here's the output:
<p>
<hr>
<pre>

(derived1 101) (derived2 201) (derived2 202) (derived1 102) (derived2 203) 

</pre>
<hr>

<hr>
<!WA82><!WA82><!WA82><!WA82><!WA82><!WA82><a href=#pointers>Pointers and STL</a> 
<br>
<!WA83><!WA83><!WA83><!WA83><!WA83><!WA83><a href=#index>Back to index</a>
<hr>

<a name=pointer_deriv_template><h3>
    Templated pointer wrapper that takes a pointer to the base class</h3></a>
The following example shows 2 classes derived from <tt>Base</tt>, 
<tt>derived1</tt> and <tt>derived2</tt> and a templated wrapper
<tt>Wrapper&lt;T&gt;</tt>. The wrapper class <b>assumes</b> that the base 
class provides a virtual <tt>clone</tt> facility and does the memory
management.
<p>
<em>Note: After the new'd Base derivative is passed to the 
wrapper, it owns it and deletes it in the destructor</em>.
<p>
<hr>

<PRE>
<STRONG>#include</STRONG> &lt;<!WA84><!WA84><!WA84><!WA84><!WA84><!WA84><A HREF="#stl.h">stl.h</A>&gt;
<STRONG>#include</STRONG> &lt;string.h&gt;
<STRONG>#include</STRONG> &lt;iostream.h&gt;

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> abstract base class</EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> Base <STRONG>{</STRONG>
public:
    <STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> typename_<STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>=</STRONG> 0<STRONG>;</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>=</STRONG> 0<STRONG>;</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Base<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>;</STRONG>

public:
    <STRONG>static</STRONG> <STRONG>int</STRONG> count<STRONG>;</STRONG>

protected:
    Base<STRONG>(</STRONG><STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>)</STRONG><STRONG>;</STRONG>
    Base<STRONG>(</STRONG><STRONG>const</STRONG> Base<STRONG>&amp;</STRONG> base<STRONG>)</STRONG><STRONG>;</STRONG>

private:
    <STRONG>char</STRONG><STRONG>*</STRONG> typename_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

Base::Base<STRONG>(</STRONG><STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> typename<STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>const</STRONG> <STRONG>char</STRONG><STRONG>*</STRONG> tname <STRONG>=</STRONG> <STRONG>(</STRONG>typename<STRONG>)</STRONG> <STRONG>?</STRONG> typename <STRONG>:</STRONG> &quot;<EM>unknown</EM>&quot;<STRONG>;</STRONG>
    strcpy<STRONG>(</STRONG>typename_ <STRONG>=</STRONG> <STRONG>new</STRONG> <STRONG>char</STRONG><STRONG>[</STRONG>strlen<STRONG>(</STRONG>tname<STRONG>)</STRONG> <STRONG>+</STRONG> 1<STRONG>]</STRONG><STRONG>,</STRONG> tname<STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>++</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

Base::Base<STRONG>(</STRONG><STRONG>const</STRONG> Base<STRONG>&amp;</STRONG> base<STRONG>)</STRONG> <STRONG>{</STRONG>
    strcpy<STRONG>(</STRONG>
        typename_ <STRONG>=</STRONG> <STRONG>new</STRONG> <STRONG>char</STRONG><STRONG>[</STRONG>strlen<STRONG>(</STRONG>base<STRONG>.</STRONG>typename_<STRONG>)</STRONG> <STRONG>+</STRONG> 1<STRONG>]</STRONG><STRONG>,</STRONG> base<STRONG>.</STRONG>typename_
    <STRONG>)</STRONG><STRONG>;</STRONG>
    <STRONG>++</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

Base::~Base<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG>
    <STRONG>delete</STRONG><STRONG>[</STRONG><STRONG>]</STRONG> typename_<STRONG>;</STRONG>
    <STRONG>--</STRONG>count<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> First derived class. </EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> Derived1 <STRONG>:</STRONG> <STRONG>public</STRONG> Base <STRONG>{</STRONG>
public:
    Derived1<STRONG>(</STRONG><STRONG>int</STRONG> data<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived1</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>data<STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    Derived1<STRONG>(</STRONG><STRONG>const</STRONG> Derived1<STRONG>&amp;</STRONG> d<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived1</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>d<STRONG>.</STRONG>data<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Derived1<STRONG>(</STRONG><STRONG>)</STRONG>        <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> <STRONG>new</STRONG> Derived1<STRONG>(</STRONG><STRONG>*</STRONG><STRONG>this</STRONG><STRONG>)</STRONG><STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG><STRONG>;</STRONG>
    <STRONG>int</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> data_<STRONG>;</STRONG> <STRONG>}</STRONG>
private:
    <STRONG>int</STRONG> data_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

<STRONG>virtual</STRONG> <STRONG>void</STRONG> Derived1::identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG>
    os <STRONG>&lt;&lt;</STRONG> &quot;<EM>(</EM>&quot; <STRONG>&lt;&lt;</STRONG> typename<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM> </EM>&quot; <STRONG>&lt;&lt;</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>&lt;&lt;</STRONG> &quot;<EM>)</EM>&quot;<STRONG>;</STRONG>
<STRONG>}</STRONG>

<EM><STRONG>//</STRONG></EM>
<EM><STRONG>//</STRONG> Second derived class. </EM>
<EM><STRONG>//</STRONG></EM>
<STRONG>class</STRONG> Derived2 <STRONG>:</STRONG> <STRONG>public</STRONG> Base <STRONG>{</STRONG>
public:
    Derived2<STRONG>(</STRONG><STRONG>int</STRONG> data<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived2</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>data<STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    Derived2<STRONG>(</STRONG><STRONG>const</STRONG> Derived2<STRONG>&amp;</STRONG> d<STRONG>)</STRONG> <STRONG>:</STRONG> Base<STRONG>(</STRONG>&quot;<EM>derived2</EM>&quot;<STRONG>)</STRONG><STRONG>,</STRONG> data_<STRONG>(</STRONG>d<STRONG>.</STRONG>data<STRONG>(</STRONG><STRONG>)</STRONG><STRONG>)</STRONG> <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>~</STRONG>Derived2<STRONG>(</STRONG><STRONG>)</STRONG>        <STRONG>{</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> Base<STRONG>*</STRONG> clone<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> <STRONG>new</STRONG> Derived2<STRONG>(</STRONG><STRONG>*</STRONG><STRONG>this</STRONG><STRONG>)</STRONG><STRONG>;</STRONG> <STRONG>}</STRONG>
    <STRONG>virtual</STRONG> <STRONG>void</STRONG> identify<STRONG>(</STRONG>ostream<STRONG>&amp;</STRONG> os<STRONG>)</STRONG> <STRONG>const</STRONG><STRONG>;</STRONG>
    <STRONG>int</STRONG> data<STRONG>(</STRONG><STRONG>)</STRONG> <STRONG>const</STRONG> <STRONG>{</STRONG> <STRONG>return</STRONG> data_<STRONG>;</STRONG> <STRONG>}</STRONG>
private:
    <STRONG>int</STRONG> data_<STRONG>;</STRONG>
<STRONG>}</STRONG><STRONG>;</STRONG>

<STRONG>virtual</STRONG> <STRONG>void</STRONG> Derived2::identify<STRONG>(</STRONG>ostream<STR