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15<h1>Shared Container Iterator</h1>
16
17Defined in header
18<a href="../../boost/shared_container_iterator.hpp">boost/shared_container_iterator.hpp</a>
19
20<p>
21The purpose of the shared container iterator is to attach the lifetime
22of a container to the lifetime of its iterators. In other words, the
23container will not be deleted until after all its iterators are
24destroyed.  The shared container iterator is typically used to
25implement functions that return iterators over a range of objects that
26only need to exist for the lifetime of the iterators.  By returning a
27pair of shared iterators from a function, the callee can return a
28heap-allocated range of objects whose lifetime is automatically managed.
29<p>
30The shared container iterator augments an iterator over a shared
31container.  It maintains a reference count on the shared
32container. If only shared container iterators hold references to
33the container, the container's lifetime will end when the last shared
34container iterator over it is destroyed.  In any case, the shared
35container is guaranteed to persist beyond the lifetime of all
36the iterators. In all other ways, the
37shared container iterator behaves the same as its base iterator.
38
39
40<h2>Synopsis</h2>
41
42<pre>
43namespace boost {
44  template &lt;typename <a href="http://www.sgi.com/tech/stl/Container.html">Container</a>&gt;
45  class shared_container_iterator;
46
47  template &lt;typename <a href="http://www.sgi.com/tech/stl/Container.html">Container</a>&gt;
48  shared_container_iterator&lt;Container&gt;
49  make_shared_container_iterator(typename Container::iterator base,
50    boost::shared_ptr&lt;Container&gt; const&amp; container);
51
52  std::pair&lt;
53    typename shared_container_iterator&lt;Container&gt;,
54    typename shared_container_iterator&lt;Container&gt;
55  &gt;
56  make_shared_container_range(boost::shared_ptr&lt;Container&gt; const&amp; container);
57}
58</pre>
59
60<hr>
61
62<h2><a name="generator">The Shared Container Iterator Type</a></h2>
63
64<pre>
65template &lt;typename Container&gt; class shared_container_iterator;
66</pre>
67
68The class template <tt>shared_container_iterator</tt> 
69is the shared container iterator type.  The <tt>Container</tt> template
70type argument must model the
71<a href="http://www.sgi.com/tech/stl/Container.html">Container</a>
72concept.
73
74<h3>Example</h3>
75
76<p>
77The following example illustrates how to create an iterator that
78regulates the lifetime of a reference counted <tt>std::vector</tt>.
79Though the original shared pointer <tt>ints</tt> ceases to exist
80after <tt>set_range()</tt> returns, the
81<tt>shared_counter_iterator</tt> objects maintain references to the
82      underlying vector and thereby extend the container's lifetime.
83<p>
84<a href="./shared_iterator_example1.cpp">shared_iterator_example1.cpp</a>:
85<PRE>
86<font color="#008040">#include "shared_container_iterator.hpp"</font>
87<font color="#008040">#include "boost/shared_ptr.hpp"</font>
88<font color="#008040">#include &lt;algorithm&gt;</font>
89<font color="#008040">#include &lt;iostream&gt;</font>
90<font color="#008040">#include &lt;vector&gt;</font>
91
92<B>typedef</B> boost::shared_container_iterator&lt; std::vector&lt;<B>int</B>&gt; &gt; iterator;
93
94
95<B>void</B> set_range(iterator& i, iterator& end)  {
96
97  boost::shared_ptr&lt; std::vector&lt;<B>int</B>&gt; &gt; ints(<B>new</B> std::vector&lt;<B>int</B>&gt;());
98 
99  ints-&gt;push_back(<font color="#0000A0">0</font>);
100  ints-&gt;push_back(<font color="#0000A0">1</font>);
101  ints-&gt;push_back(<font color="#0000A0">2</font>);
102  ints-&gt;push_back(<font color="#0000A0">3</font>);
103  ints-&gt;push_back(<font color="#0000A0">4</font>);
104  ints-&gt;push_back(<font color="#0000A0">5</font>);
105 
106  i = iterator(ints-&gt;begin(),ints);
107  end = iterator(ints-&gt;end(),ints);
108}
109
110
111<B>int</B> main() {
112
113  iterator i,end;
114
115  set_range(i,end);
116
117  std::copy(i,end,std::ostream_iterator&lt;<B>int</B>&gt;(std::cout,<font color="#0000FF">","</font>));
118  std::cout.put(<font color="#0000FF">'\n'</font>);
119
120  <B>return</B> <font color="#0000A0">0</font>;
121}
122</PRE>
123
124The output from this part is:
125<pre>
1260,1,2,3,4,5,
127</pre>
128
129<h3>Template Parameters</h3>
130
131<Table border>
132<TR>
133<TH>Parameter</TH><TH>Description</TH>
134</TR>
135
136<TR>
137<TD><a
138href="http://www.sgi.com/tech/stl/Container.html"><tt>Container</tt></a></TD>
139<TD>The type of the container that we wish to iterate over. It must be
140a model of the
141<a href="http://www.sgi.com/tech/stl/Container.html"><tt>Container</tt></a>
142concept.
143</TD>
144</TR>
145</Table>
146
147<h3>Model of</h3>
148
149The <tt>shared_container_iterator<Container></tt> type models the
150same iterator concept as the base iterator
151    (<tt>Container::iterator</tt>).
152
153<h3>Members</h3>
154
155The shared container iterator type implements the member functions and
156operators required of the <a
157href="http://www.sgi.com/tech/stl/RandomAccessIterator.html">Random Access Iterator</a>
158concept, though only operations defined for the base iterator will be valid.
159In addition it has the following constructor:
160
161<pre>
162shared_container_iterator(Container::iterator const&amp; it,
163                          boost::shared_ptr&lt;Container&gt; const&amp; container)
164</pre>
165
166<p>
167<hr>
168<p>
169
170
171<h2><a name="make_iterator">The Shared Container Iterator Object Generator</a></h2>
172
173<pre>
174template &lt;typename Container&gt;
175shared_container_iterator&lt;Container&gt;
176make_shared_container_iterator(Container::iterator base,
177                               boost::shared_ptr&lt;Container&gt; const&amp; container)
178</pre>
179
180This function provides an alternative to directly constructing a
181shared container iterator.  Using the object generator, a shared
182container iterator can be created and passed to a function without
183explicitly specifying its type.
184
185<h3>Example</h3>
186
187This example, similar to the previous, uses
188<tt>make_shared_container_iterator()</tt> to create the iterators.
189
190<p>
191<a href="./shared_iterator_example2.cpp">shared_iterator_example2.cpp</a>:
192
193<PRE>
194<font color="#008040">#include "shared_container_iterator.hpp"</font>
195<font color="#008040">#include "boost/shared_ptr.hpp"</font>
196<font color="#008040">#include &lt;algorithm&gt;</font>
197<font color="#008040">#include &lt;iterator&gt;</font>
198<font color="#008040">#include &lt;iostream&gt;</font>
199<font color="#008040">#include &lt;vector&gt;</font>
200
201
202<B>template</B> &lt;<B>typename</B> Iterator&gt;
203<B>void</B> print_range_nl (Iterator begin, Iterator end) {
204  <B>typedef</B> <B>typename</B> std::iterator_traits&lt;Iterator&gt;::value_type val;
205  std::copy(begin,end,std::ostream_iterator&lt;val&gt;(std::cout,<font color="#0000FF">","</font>));
206  std::cout.put(<font color="#0000FF">'\n'</font>);
207}
208
209
210<B>int</B> main() {
211
212  <B>typedef</B> boost::shared_ptr&lt; std::vector&lt;<B>int</B>&gt; &gt; ints_t;
213  {
214    ints_t ints(<B>new</B> std::vector&lt;<B>int</B>&gt;());
215
216    ints-&gt;push_back(<font color="#0000A0">0</font>);
217    ints-&gt;push_back(<font color="#0000A0">1</font>);
218    ints-&gt;push_back(<font color="#0000A0">2</font>);
219    ints-&gt;push_back(<font color="#0000A0">3</font>);
220    ints-&gt;push_back(<font color="#0000A0">4</font>);
221    ints-&gt;push_back(<font color="#0000A0">5</font>);
222
223    print_range_nl(boost::make_shared_container_iterator(ints-&gt;begin(),ints),
224                   boost::make_shared_container_iterator(ints-&gt;end(),ints));
225  }
226 
227
228
229  <B>return</B> <font color="#0000A0">0</font>;
230}
231</PRE>
232
233Observe that the <tt>shared_container_iterator</tt> type is never
234explicitly named. The output from this example is the same as the previous.
235
236<h2><a name="make_range">The Shared Container Iterator Range Generator</a></h2>
237
238<pre>
239template &lt;typename Container&gt;
240std::pair&lt
241  shared_container_iterator&lt;Container&gt;,
242  shared_container_iterator&lt;Container&gt;
243&gt;
244make_shared_container_range(boost::shared_ptr&lt;Container&gt; const&amp; container);
245</pre>
246
247Class <tt>shared_container_iterator</tt> is meant primarily to return,
248using iterators, a range of values that we can guarantee will be alive as
249long as the iterators are. This is a convenience
250function to do just that. It is equivalent to
251
252<pre>
253std::make_pair(make_shared_container_iterator(container-&gt;begin(),container),
254               make_shared_container_iterator(container-&gt;end(),container));
255</pre>
256
257<h3>Example</h3>
258
259In the following example, a range of values is returned as a pair of
260<tt>shared_container_iterator</tt> objects. 
261
262
263<p>
264<a href="./shared_iterator_example3.cpp">shared_iterator_example3.cpp</a>:
265
266<PRE>
267<font color="#008040">#include "shared_container_iterator.hpp"</font>
268<font color="#008040">#include "boost/shared_ptr.hpp"</font>
269<font color="#008040">#include "boost/tuple/tuple.hpp" // for boost::tie</font>
270<font color="#008040">#include &lt;algorithm&gt;              // for std::copy</font>
271<font color="#008040">#include &lt;iostream&gt;              </font>
272<font color="#008040">#include &lt;vector&gt;</font>
273
274
275<B>typedef</B> boost::shared_container_iterator&lt; std::vector&lt;<B>int</B>&gt; &gt; iterator;
276
277std::pair&lt;iterator,iterator&gt;
278return_range() {
279  boost::shared_ptr&lt; std::vector&lt;<B>int</B>&gt; &gt; range(<B>new</B> std::vector&lt;<B>int</B>&gt;());
280  range-&gt;push_back(<font color="#0000A0">0</font>);
281  range-&gt;push_back(<font color="#0000A0">1</font>);
282  range-&gt;push_back(<font color="#0000A0">2</font>);
283  range-&gt;push_back(<font color="#0000A0">3</font>);
284  range-&gt;push_back(<font color="#0000A0">4</font>);
285  range-&gt;push_back(<font color="#0000A0">5</font>);
286  <B>return</B> boost::make_shared_container_range(range);
287}
288
289
290<B>int</B> main() {
291
292
293  iterator i,end;
294 
295  boost::tie(i,end) = return_range();
296
297  std::copy(i,end,std::ostream_iterator&lt;<B>int</B>&gt;(std::cout,<font color="#0000FF">","</font>));
298  std::cout.put(<font color="#0000FF">'\n'</font>);
299
300  <B>return</B> <font color="#0000A0">0</font>;
301}
302</PRE>
303
304Though the <tt>range</tt> object only lives for the duration of the
305<tt>return_range</tt> call, the reference counted
306<tt>std::vector</tt> will live until <tt>i</tt> and <tt>end</tt>
307are both destroyed.  The output from this example is the same as
308the previous two.
309
310
311<hr>
312<!-- hhmts start -->
313Last modified: Mon Aug 11 11:27:03 EST 2003
314<!-- hhmts end -->
315<p>© Copyright 2003 The Trustees of Indiana University.
316 Use, modification and distribution is subject to the Boost Software
317 License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
318 http:www.boost.org/LICENSE_1_0.txt)</p>
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