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 <body>
 <div class="document" id="boost-pointer-container-library">
 <h1 class="title"><img alt="Boost" src="boost.png" /> Pointer Container Library</h1>
 <h2 class="subtitle" id="examples">Examples</h2>
 <p>Some examples are given here and in the accompanying test files:</p>
 <div class="contents local topic">
 <ul class="simple">
 <li><a class="reference" href="#null-pointers-cannot-be-stored-in-the-containers" id="id2" name="id2">1. Null pointers cannot be stored in the containers</a></li>
 <li><a class="reference" href="#iterators-and-other-operations-return-indirected-values" id="id3" name="id3">2. Iterators and other operations return indirected values</a></li>
 <li><a class="reference" href="#copy-semantics-of-pointer-containers" id="id4" name="id4">3. Copy-semantics of pointer containers</a></li>
 <li><a class="reference" href="#making-a-non-copyable-type-cloneable" id="id5" name="id5">4. Making a non-copyable type Cloneable</a></li>
 <li><a class="reference" href="#objects-are-cloned-before-insertion-inserted-pointers-are-owned-by-the-container" id="id6" name="id6">5. Objects are cloned before insertion, inserted pointers are owned by the container</a></li>
 <li><a class="reference" href="#transferring-ownership-of-a-single-element" id="id7" name="id7">6. Transferring ownership of a single element</a></li>
 <li><a class="reference" href="#transferring-ownership-of-pointers-between-different-pointer-containers" id="id8" name="id8">7. Transferring ownership of pointers between different pointer containers</a></li>
 <li><a class="reference" href="#selected-test-files" id="id9" name="id9">8. Selected test files</a></li>
 <li><a class="reference" href="#a-large-example" id="id10" name="id10">9. A large example</a></li>
 </ul>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id2" id="null-pointers-cannot-be-stored-in-the-containers" name="null-pointers-cannot-be-stored-in-the-containers"><span id="example-1"></span>1. Null pointers cannot be stored in the containers</a></h1>
 <pre class="literal-block">
 my_container.push_back( 0 );            // throws bad_ptr
 my_container.replace( an_iterator, 0 ); // throws bad_ptr
 my_container.insert( an_iterator, 0 );  // throws bad_ptr
 std::auto_ptr&lt;T&gt; p( 0 );
 my_container.push_back( p );            // throws bad_ptr
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id3" id="iterators-and-other-operations-return-indirected-values" name="iterators-and-other-operations-return-indirected-values"><span id="example-2"></span>2. Iterators and other operations return indirected values</a></h1>
 <pre class="literal-block">
 ptr_vector&lt;X&gt; pvec;
 std::vector&lt;X*&gt; vec;
 *vec.begin()  = new X;   // fine, memory leak
 *pvec.begin() = new X;   // compile time error
 ( *vec.begin() )-&gt;foo(); // call X::foo(), a bit clumsy
 pvec.begin()-&gt;foo();     // no indirection needed
 *vec.front()  = X();     // overwrite first element
 pvec.front()  = X();     // no indirection needed
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id4" id="copy-semantics-of-pointer-containers" name="copy-semantics-of-pointer-containers"><span id="example-3"></span>3. Copy-semantics of pointer containers</a></h1>
 <pre class="literal-block">
 ptr_vector&lt;T&gt; vec1;
 ...
 ptr_vector&lt;T&gt; vec2( vec1.clone() ); // deep copy objects of 'vec1' and use them to construct 'vec2', could be very expensive
 vec2 = vec1.release();              // give up ownership of pointers in 'vec1' and pass the ownership to 'vec2', rather cheap
 vec2.release();                     // give up ownership; the objects will be deallocated if not assigned to another container
 vec1 = vec2;                        // deep copy objects of 'vec2' and assign them to 'vec1', could be very expensive
 ptr_vector&lt;T&gt; vec3( vec1 );         // deep copy objects of 'vec1', could be very expensive
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id5" id="making-a-non-copyable-type-cloneable" name="making-a-non-copyable-type-cloneable"><span id="example-4"></span>4. Making a non-copyable type Cloneable</a></h1>
 <pre class="literal-block">
  // a class that has no normal copy semantics
 class X : boost::noncopyable { public: X* clone() const; ... };

 // this will be found by the library by argument dependent lookup (ADL)
 X* new_clone( const X&amp; x )
 { return x.clone(); }

 // we can now use the interface that requires cloneability
 ptr_vector&lt;X&gt; vec1, vec2;
 ...
 vec2 = vec1.clone();                                 // 'clone()' requires cloning &lt;g&gt;
 vec2.insert( vec2.end(), vec1.begin(), vec1.end() ); // inserting always means inserting clones
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id6" id="objects-are-cloned-before-insertion-inserted-pointers-are-owned-by-the-container" name="objects-are-cloned-before-insertion-inserted-pointers-are-owned-by-the-container"><span id="example-5"></span>5. Objects are cloned before insertion, inserted pointers are owned by the container</a></h1>
 <pre class="literal-block">
 class X { ... };                     // assume 'X' is Cloneable
 X x;                                 // and 'X' can be stack-allocated
 ptr_list&lt;X&gt; list;
 list.push_back( new_clone( x ) );    // insert a clone
 list.push_back( new X );             // always give the pointer directly to the container to avoid leaks
 list.push_back( &amp;x );                // don't do this!!!
 std::auto_ptr&lt;X&gt; p( new X );
 list.push_back( p );                 // give up ownership
 BOOST_ASSERT( p.get() == 0 );
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id7" id="transferring-ownership-of-a-single-element" name="transferring-ownership-of-a-single-element"><span id="example-6"></span>6. Transferring ownership of a single element</a></h1>
 <pre class="literal-block">
 ptr_deque&lt;T&gt;                    deq;
 typedef ptr_deque&lt;T&gt;::auto_type auto_type;

 // ... fill the container somehow

 auto_type ptr  = deq.pop_back();                 // remove back element from container and give up ownership
 auto_type ptr2 = deq.release( deq.begin() + 2 ); // use an iterator to determine the element to release
 ptr            = deq.pop_front();                // supported for 'ptr_list' and 'ptr_deque'

 deq.push_back( ptr.release() );                  // give ownership back to the container
 </pre>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id8" id="transferring-ownership-of-pointers-between-different-pointer-containers" name="transferring-ownership-of-pointers-between-different-pointer-containers"><span id="example-7"></span>7. Transferring ownership of pointers between different pointer containers</a></h1>
 <pre class="literal-block">
 ptr_list&lt;X&gt; list; ptr_vector&lt;X&gt; vec;
 ...
 //
 // note: no cloning happens in these examples
 //
 list.transfer( list.begin(), vec.begin(), vec );           // make the first element of 'vec' the first element of 'list'
 vec.transfer( vec.end(), list.begin(), list.end(), list ); // put all the lists element into the vector
 </pre>
 <p>We can also transfer objects from <tt class="docutils literal"><span class="pre">ptr_container&lt;Derived&gt;</span></tt> to <tt class="docutils literal"><span class="pre">ptr_container&lt;Base&gt;</span></tt> without any problems.</p>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id9" id="selected-test-files" name="selected-test-files"><span id="example-8"></span>8. Selected test files</a></h1>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field"><th class="field-name" colspan="2"><a class="reference" href="../test/incomplete_type_test.cpp">incomplete_type_test.cpp</a>:</th></tr>
 <tr><td>&nbsp;</td><td class="field-body">Shows how to implement the Composite pattern.</td>
 </tr>
 <tr class="field"><th class="field-name" colspan="2"><a class="reference" href="../test/simple_test.cpp">simple_test.cpp</a>:</th></tr>
 <tr><td>&nbsp;</td><td class="field-body">Shows how the usage of pointer container compares with a
 container of smart pointers</td>
 </tr>
 <tr class="field"><th class="field-name" colspan="2"><a class="reference" href="../test/view_example.cpp">view_example.cpp</a>:</th></tr>
 <tr><td>&nbsp;</td><td class="field-body">Shows how to use a pointer container as a view into other container</td>
 </tr>
 <tr class="field"><th class="field-name"><a class="reference" href="../test/tree_test.cpp">tree_test.cpp</a>:</th><td class="field-body">Shows how to make a tree-structure</td>
 </tr>
 <tr class="field"><th class="field-name"><a class="reference" href="../test/ptr_array.cpp">array_test.cpp</a>:</th><td class="field-body">Shows how to make an n-ary tree</td>
 </tr>
 </tbody>
 </table>
 </div>
 <div class="section">
 <h1><a class="toc-backref" href="#id10" id="a-large-example" name="a-large-example">9. A large example</a></h1>
 <p>This example shows many of the most common
 features at work. The example provide lots of comments.
 The source code can also be found <a class="reference" href="../test/tut1.cpp">here</a>.</p>
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
 <title> </title>
 <link rel="stylesheet" href="default.css" type="text/css">
 </head>

 <body>
     <pre><span class=comment>//
 // Boost.Pointer Container
 //
 //  Copyright Thorsten Ottosen 2003-2005. Use, modification and
 //  distribution is subject to the Boost Software License, Version
 //  1.0. (See accompanying file LICENSE_1_0.txt or copy at
 //  http://www.boost.org/LICENSE_1_0.txt)
 //
 // For more information, see http://www.boost.org/libs/ptr_container/
 //

 //
 // This example is intended to get you started.
 // Notice how the smart container
 //
 // 1. takes ownership of objects
 // 2. transfers ownership
 // 3. applies indirection to iterators
 // 4. clones objects from other smart containers
 //

 //
 // First we select which container to use.
 //</span>
 <span class=preprocessor>#include</span> <span class=special>&lt;</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>ptr_container</span><span class=special>/</span><span class=identifier>ptr_deque</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>&gt;</span>

 <span class=comment>//
 // we need these later in the example
 //</span>
 <span class=preprocessor>#include</span> <span class=special>&lt;</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>assert</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>&gt;</span>
 <span class=preprocessor>#include</span> <span class=special>&lt;</span><span class=identifier>string</span><span class=special>&gt;</span>
 <span class=preprocessor>#include</span> <span class=special>&lt;</span><span class=identifier>exception</span><span class=special>&gt;</span>


 <span class=comment>//
 // Then we define a small polymorphic class
 // hierarchy.
 //</span>

 <span class=keyword>class</span> <span class=identifier>animal</span> <span class=special>:</span> <span class=identifier>boost</span><span class=special>::</span><span class=identifier>noncopyable</span>
 <span class=special>{</span>
     <span class=keyword>virtual</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>do_speak</span><span class=special>()</span> <span class=keyword>const</span> <span class=special>=</span> <span class=number>0</span><span class=special>;</span>
     <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>name_</span><span class=special>;</span>

 <span class=keyword>protected</span><span class=special>:</span>
     <span class=comment>//
     // Animals cannot be copied...
     //</span>
     <span class=identifier>animal</span><span class=special>(</span> <span class=keyword>const</span> <span class=identifier>animal</span><span class=special>&amp;</span> <span class=identifier>r</span> <span class=special>)</span> <span class=special>:</span> <span class=identifier>name_</span><span class=special>(</span> <span class=identifier>r</span><span class=special>.</span><span class=identifier>name_</span> <span class=special>)</span>           <span class=special>{</span> <span class=special>}</span>
     <span class=keyword>void</span> <span class=keyword>operator</span><span class=special>=(</span> <span class=keyword>const</span> <span class=identifier>animal</span><span class=special>&amp;</span> <span class=special>);</span>

 <span class=keyword>private</span><span class=special>:</span>
     <span class=comment>//
     // ...but due to advances in genetics, we can clone them!
     //</span>

     <span class=keyword>virtual</span> <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>do_clone</span><span class=special>()</span> <span class=keyword>const</span> <span class=special>=</span> <span class=number>0</span><span class=special>;</span>

 <span class=keyword>public</span><span class=special>:</span>
     <span class=identifier>animal</span><span class=special>(</span> <span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&amp;</span> <span class=identifier>name</span> <span class=special>)</span> <span class=special>:</span> <span class=identifier>name_</span><span class=special>(</span><span class=identifier>name</span><span class=special>)</span>        <span class=special>{</span> <span class=special>}</span>
     <span class=keyword>virtual</span> <span class=special>~</span><span class=identifier>animal</span><span class=special>()</span> <span class=keyword>throw</span><span class=special>()</span>                              <span class=special>{</span> <span class=special>}</span>

     <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>speak</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>do_speak</span><span class=special>();</span>
     <span class=special>}</span>

     <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>name</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>name_</span><span class=special>;</span>
     <span class=special>}</span>

     <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>clone</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>do_clone</span><span class=special>();</span>
     <span class=special>}</span>
 <span class=special>};</span>

 <span class=comment>//
 // An animal is still not Clonable. We need this last hook.
 //
 // Notice that we pass the animal by const reference
 // and return by pointer.
 //</span>

 <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>new_clone</span><span class=special>(</span> <span class=keyword>const</span> <span class=identifier>animal</span><span class=special>&amp;</span> <span class=identifier>a</span> <span class=special>)</span>
 <span class=special>{</span>
     <span class=keyword>return</span> <span class=identifier>a</span><span class=special>.</span><span class=identifier>clone</span><span class=special>();</span>
 <span class=special>}</span>

 <span class=comment>//
 // We do not need to define 'delete_clone()' since
 // since the default is to call the default 'operator delete()'.
 //</span>

 <span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>muuuh</span> <span class=special>=</span> <span class=string>&quot;Muuuh!&quot;</span><span class=special>;</span>
 <span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>oiink</span> <span class=special>=</span> <span class=string>&quot;Oiiink&quot;</span><span class=special>;</span>

 <span class=keyword>class</span> <span class=identifier>cow</span> <span class=special>:</span> <span class=keyword>public</span> <span class=identifier>animal</span>
 <span class=special>{</span>
     <span class=keyword>virtual</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>do_speak</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>muuuh</span><span class=special>;</span>
     <span class=special>}</span>

     <span class=keyword>virtual</span> <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>do_clone</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=keyword>new</span> <span class=identifier>cow</span><span class=special>(</span> <span class=special>*</span><span class=keyword>this</span> <span class=special>);</span>
     <span class=special>}</span>

 <span class=keyword>public</span><span class=special>:</span>
     <span class=identifier>cow</span><span class=special>(</span> <span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&amp;</span> <span class=identifier>name</span> <span class=special>)</span> <span class=special>:</span> <span class=identifier>animal</span><span class=special>(</span><span class=identifier>name</span><span class=special>)</span>          <span class=special>{</span> <span class=special>}</span>
 <span class=special>};</span>

 <span class=keyword>class</span> <span class=identifier>pig</span> <span class=special>:</span> <span class=keyword>public</span> <span class=identifier>animal</span>
 <span class=special>{</span>
     <span class=keyword>virtual</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>do_speak</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>oiink</span><span class=special>;</span>
     <span class=special>}</span>

     <span class=keyword>virtual</span> <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>do_clone</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=keyword>new</span> <span class=identifier>pig</span><span class=special>(</span> <span class=special>*</span><span class=keyword>this</span> <span class=special>);</span>
     <span class=special>}</span>

 <span class=keyword>public</span><span class=special>:</span>
     <span class=identifier>pig</span><span class=special>(</span> <span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&amp;</span> <span class=identifier>name</span> <span class=special>)</span> <span class=special>:</span> <span class=identifier>animal</span><span class=special>(</span><span class=identifier>name</span><span class=special>)</span>          <span class=special>{</span> <span class=special>}</span>
 <span class=special>};</span>

 <span class=comment>//
 // Then we, of course, need a place to put all
 // those animals.
 //</span>

 <span class=keyword>class</span> <span class=identifier>farm</span>
 <span class=special>{</span>
     <span class=comment>//
     // This is where the smart containers are handy
     //</span>
     <span class=keyword>typedef</span> <span class=identifier>boost</span><span class=special>::</span><span class=identifier>ptr_deque</span><span class=special>&lt;</span><span class=identifier>animal</span><span class=special>&gt;</span> <span class=identifier>barn_type</span><span class=special>;</span>
     <span class=identifier>barn_type</span>                        <span class=identifier>barn</span><span class=special>;</span>

     <span class=comment>//
     // An error type
     //</span>
     <span class=keyword>struct</span> <span class=identifier>farm_trouble</span> <span class=special>:</span> <span class=keyword>public</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>exception</span>           <span class=special>{</span> <span class=special>};</span>

 <span class=keyword>public</span><span class=special>:</span>
     <span class=comment>//
     // We would like to make it possible to
     // iterate over the animals in the farm
     //</span>
     <span class=keyword>typedef</span> <span class=identifier>barn_type</span><span class=special>::</span><span class=identifier>iterator</span>  <span class=identifier>animal_iterator</span><span class=special>;</span>

     <span class=comment>//
     // We also need to count the farm's size...
     //</span>
     <span class=keyword>typedef</span> <span class=identifier>barn_type</span><span class=special>::</span><span class=identifier>size_type</span> <span class=identifier>size_type</span><span class=special>;</span>

     <span class=comment>//
     // And we also want to transfer an animal
     // safely around. The easiest way to think
     // about '::auto_type' is to imagine a simplified
     // 'std::auto_ptr&lt;T&gt;' ... this means you can expect
     //
     //   T* operator-&gt;()
     //   T* release()
     //   deleting destructor
     //
     // but not more.
     //</span>
     <span class=keyword>typedef</span> <span class=identifier>barn_type</span><span class=special>::</span><span class=identifier>auto_type</span>  <span class=identifier>animal_transport</span><span class=special>;</span>

     <span class=comment>//
     // Create an empty farm.
     //</span>
     <span class=identifier>farm</span><span class=special>()</span>                                                 <span class=special>{</span> <span class=special>}</span>

     <span class=comment>//
     // We need a constructor that can make a new
     // farm by cloning a range of animals.
     //</span>
     <span class=identifier>farm</span><span class=special>(</span> <span class=identifier>animal_iterator</span> <span class=identifier>begin</span><span class=special>,</span> <span class=identifier>animal_iterator</span> <span class=identifier>end</span> <span class=special>)</span>
      <span class=special>:</span>
         <span class=comment>//
         // Objects are always cloned before insertion
         // unless we explicitly add a pointer or
         // use 'release()'. Therefore we actually
         // clone all animals in the range
         //</span>
         <span class=identifier>barn</span><span class=special>(</span> <span class=identifier>begin</span><span class=special>,</span> <span class=identifier>end</span> <span class=special>)</span>                               <span class=special>{</span> <span class=special>}</span>

     <span class=comment>//
     // ... so we need some other function too
     //</span>

     <span class=identifier>animal_iterator</span> <span class=identifier>begin</span><span class=special>()</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>begin</span><span class=special>();</span>
     <span class=special>}</span>

     <span class=identifier>animal_iterator</span> <span class=identifier>end</span><span class=special>()</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>end</span><span class=special>();</span>
     <span class=special>}</span>

     <span class=comment>//
     // Here it is quite ok to have an 'animal*' argument.
     // The smart container will handle all ownership
     // issues.
     //</span>
     <span class=keyword>void</span> <span class=identifier>buy_animal</span><span class=special>(</span> <span class=identifier>animal</span><span class=special>*</span> <span class=identifier>a</span> <span class=special>)</span>
     <span class=special>{</span>
         <span class=identifier>barn</span><span class=special>.</span><span class=identifier>push_back</span><span class=special>(</span> <span class=identifier>a</span> <span class=special>);</span>
     <span class=special>}</span>

     <span class=comment>//
     // The farm can also be in economical trouble and
     // therefore be in the need to sell animals.
     //</span>
     <span class=identifier>animal_transport</span> <span class=identifier>sell_animal</span><span class=special>(</span> <span class=identifier>animal_iterator</span> <span class=identifier>to_sell</span> <span class=special>)</span>
     <span class=special>{</span>
         <span class=keyword>if</span><span class=special>(</span> <span class=identifier>to_sell</span> <span class=special>==</span> <span class=identifier>end</span><span class=special>()</span> <span class=special>)</span>
             <span class=keyword>throw</span> <span class=identifier>farm_trouble</span><span class=special>();</span>

         <span class=comment>//
         // Here we remove the animal from the barn,
         // but the animal is not deleted yet...it's
         // up to the buyer to decide what
         // to do with it.
         //</span>
         <span class=keyword>return</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>release</span><span class=special>(</span> <span class=identifier>to_sell</span> <span class=special>);</span>
     <span class=special>}</span>

     <span class=comment>//
     // How big a farm do we have?
     //</span>
     <span class=identifier>size_type</span> <span class=identifier>size</span><span class=special>()</span> <span class=keyword>const</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>size</span><span class=special>();</span>
     <span class=special>}</span>

     <span class=comment>//
     // If things are bad, we might choose to sell all animals :-(
     //</span>
     <span class=identifier>std</span><span class=special>::</span><span class=identifier>auto_ptr</span><span class=special>&lt;</span><span class=identifier>barn_type</span><span class=special>&gt;</span> <span class=identifier>sell_farm</span><span class=special>()</span>
     <span class=special>{</span>
         <span class=keyword>return</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>release</span><span class=special>();</span>
     <span class=special>}</span>

     <span class=comment>//
     // However, if things are good, we might buy somebody
     // else's farm :-)
     //</span>

     <span class=keyword>void</span> <span class=identifier>buy_farm</span><span class=special>(</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>auto_ptr</span><span class=special>&lt;</span><span class=identifier>barn_type</span><span class=special>&gt;</span> <span class=identifier>other</span> <span class=special>)</span>
     <span class=special>{</span>
         <span class=comment>//
         // This line inserts all the animals from 'other'
         // and is guaranteed either to succeed or to have no
         // effect
         //</span>
         <span class=identifier>barn</span><span class=special>.</span><span class=identifier>transfer</span><span class=special>(</span> <span class=identifier>barn</span><span class=special>.</span><span class=identifier>end</span><span class=special>(),</span> <span class=comment>// insert new animals at the end</span>
                          <span class=special>*</span><span class=identifier>other</span> <span class=special>);</span>     <span class=comment>// we want to transfer all animals,
                                        // so we use the whole container as argument
         //
         // You might think you would have to do
         //
         // other.release();
         //
         // but '*other' is empty and can go out of scope as it wants
         //</span>
         <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>other</span><span class=special>-&gt;</span><span class=identifier>empty</span><span class=special>()</span> <span class=special>);</span>
     <span class=special>}</span>

 <span class=special>};</span> <span class=comment>// class 'farm'.</span>

 <span class=keyword>int</span> <span class=identifier>main</span><span class=special>()</span>
 <span class=special>{</span>
     <span class=comment>//
     // First we make a farm
     //</span>
     <span class=identifier>farm</span> <span class=identifier>animal_farm</span><span class=special>;</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span> <span class=special>==</span> <span class=number>0u</span> <span class=special>);</span>

     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>pig</span><span class=special>(</span><span class=string>&quot;Betty&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>pig</span><span class=special>(</span><span class=string>&quot;Benny&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>pig</span><span class=special>(</span><span class=string>&quot;Jeltzin&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>cow</span><span class=special>(</span><span class=string>&quot;Hanz&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>cow</span><span class=special>(</span><span class=string>&quot;Mary&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=keyword>new</span> <span class=identifier>cow</span><span class=special>(</span><span class=string>&quot;Frederik&quot;</span><span class=special>)</span> <span class=special>);</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span> <span class=special>==</span> <span class=number>6u</span> <span class=special>);</span>

     <span class=comment>//
     // Then we make another farm...it will actually contain
     // a clone of the other farm.
     //</span>
     <span class=identifier>farm</span> <span class=identifier>new_farm</span><span class=special>(</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>begin</span><span class=special>(),</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>end</span><span class=special>()</span> <span class=special>);</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span> <span class=special>==</span> <span class=number>6u</span> <span class=special>);</span>

     <span class=comment>//
     // Is it really clones in the new farm?
     //</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>begin</span><span class=special>()-&gt;</span><span class=identifier>name</span><span class=special>()</span> <span class=special>==</span> <span class=string>&quot;Betty&quot;</span> <span class=special>);</span>

     <span class=comment>//
     // Then we search for an animal, Mary (the Crown Princess of Denmark),
     // because we would like to buy her ...
     //</span>
     <span class=keyword>typedef</span> <span class=identifier>farm</span><span class=special>::</span><span class=identifier>animal_iterator</span> <span class=identifier>iterator</span><span class=special>;</span>
     <span class=identifier>iterator</span> <span class=identifier>to_sell</span><span class=special>;</span>
     <span class=keyword>for</span><span class=special>(</span> <span class=identifier>iterator</span> <span class=identifier>i</span>   <span class=special>=</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>begin</span><span class=special>(),</span>
                   <span class=identifier>end</span> <span class=special>=</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>end</span><span class=special>();</span>
          <span class=identifier>i</span> <span class=special>!=</span> <span class=identifier>end</span><span class=special>;</span> <span class=special>++</span><span class=identifier>i</span> <span class=special>)</span>
     <span class=special>{</span>
         <span class=keyword>if</span><span class=special>(</span> <span class=identifier>i</span><span class=special>-&gt;</span><span class=identifier>name</span><span class=special>()</span> <span class=special>==</span> <span class=string>&quot;Mary&quot;</span> <span class=special>)</span>
         <span class=special>{</span>
             <span class=identifier>to_sell</span> <span class=special>=</span> <span class=identifier>i</span><span class=special>;</span>
             <span class=keyword>break</span><span class=special>;</span>
         <span class=special>}</span>
     <span class=special>}</span>

     <span class=identifier>farm</span><span class=special>::</span><span class=identifier>animal_transport</span> <span class=identifier>mary</span> <span class=special>=</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>sell_animal</span><span class=special>(</span> <span class=identifier>to_sell</span> <span class=special>);</span>


     <span class=keyword>if</span><span class=special>(</span> <span class=identifier>mary</span><span class=special>-&gt;</span><span class=identifier>speak</span><span class=special>()</span> <span class=special>==</span> <span class=identifier>muuuh</span> <span class=special>)</span>
         <span class=comment>//
         // Great, Mary is a cow, and she may live longer
         //</span>
         <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>buy_animal</span><span class=special>(</span> <span class=identifier>mary</span><span class=special>.</span><span class=identifier>release</span><span class=special>()</span> <span class=special>);</span>
     <span class=keyword>else</span>
         <span class=comment>//
         // Then the animal would be destroyed (!)
         // when we go out of scope.
         //</span>
         <span class=special>;</span>

     <span class=comment>//
     // Now we can observe some changes to the two farms...
     //</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span> <span class=special>==</span> <span class=number>5u</span> <span class=special>);</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span>    <span class=special>==</span> <span class=number>7u</span> <span class=special>);</span>

     <span class=comment>//
     // The new farm has however underestimated how much
     // it cost to feed Mary and its owner is forced to sell the farm...
     //</span>
     <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>buy_farm</span><span class=special>(</span> <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>sell_farm</span><span class=special>()</span> <span class=special>);</span>

     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>new_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span>    <span class=special>==</span> <span class=number>0u</span> <span class=special>);</span>
     <span class=identifier>BOOST_ASSERT</span><span class=special>(</span> <span class=identifier>animal_farm</span><span class=special>.</span><span class=identifier>size</span><span class=special>()</span> <span class=special>==</span> <span class=number>12u</span> <span class=special>);</span>
 <span class=special>}</span>
 </pre>
 </body>

 </html>
 <!-- 10. Changing the Clone Allocator
 ++++++++++++++++++++++++++++++++

 This example shows how we can change
 the Clone Allocator to use the pointer containers
 as view into other containers:

 .. raw:: html
         :file: tut2.html -->
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 <tr class="field"><th class="field-name">Copyright:</th><td class="field-body">Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see <a class="reference" href="http://www.boost.org/LICENSE_1_0.txt">LICENSE_1_0.txt</a>).</td>
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