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ptr_container/doc/tutorial_example.html
Christos Stratopoulos 1ae651ac66 Delete extra space
2018-04-07 00:39:01 -04:00

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<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>//
// A convenience typedef for the compiler-appropriate
// smart pointer used to manage barns
//</span>
<span class=keyword>typedef</span> <span class=identifier><a href="compatible_smart_ptr.html"><em>compatible-smart-ptr</em></a></span><span class=special>&lt;</span><span class=identifier>barn_type</span><span class=special>&gt;</span> <span class=identifier>raii_ptr</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>raii_ptr</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>raii_ptr</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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