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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>
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<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>
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<!-- 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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