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<div class="section" title="Get the Iterator pointing to the Begin of a Container Attribute">
<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.advanced.customize.iterate.begin_container"></a><a class="link" href="begin_container.html" title="Get the Iterator pointing to the Begin of a Container Attribute">
Get the Iterator pointing to the Begin of a Container Attribute</a>
</h5></div></div></div>
<a name="spirit.advanced.customize.iterate.begin_container.begin_container"></a><h6>
<a name="id995579"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.begin_container">begin_container</a>
</h6>
<p>
The template <code class="computeroutput"><span class="identifier">begin_container</span></code>
is a type used as an attribute customization point. It is invoked by
the <span class="emphasis"><em>Karma</em></span> repetitive generators (such as <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene
(unary <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, and <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>)
in order to get an iterator pointing to the first element of the container
holding the attributes to generate output from.
</p>
<a name="spirit.advanced.customize.iterate.begin_container.module_headers"></a><h6>
<a name="id995648"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.module_headers">Module
Headers</a>
</h6>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">home</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">container</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
</p>
<div class="note" title="Note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
This header file does not need to be included directly by any user
program as it is normally included by other Spirit header files relying
on its content.
</p></td></tr>
</table></div>
<a name="spirit.advanced.customize.iterate.begin_container.namespace"></a><h6>
<a name="id995736"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.namespace">Namespace</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
<p>
Name
</p>
</th></tr></thead>
<tbody><tr><td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span></code>
</p>
</td></tr></tbody>
</table></div>
<a name="spirit.advanced.customize.iterate.begin_container.synopsis"></a><h6>
<a name="id995814"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.synopsis">Synopsis</a>
</h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">begin_container</span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">typename</span> <span class="identifier">container_iterator</span><span class="special"><</span><span class="identifier">Container</span><span class="special">>::</span><span class="identifier">type</span>
<span class="identifier">call</span><span class="special">(</span><span class="identifier">Container</span><span class="special">&</span> <span class="identifier">c</span><span class="special">);</span>
<span class="special">};</span>
</pre>
<a name="spirit.advanced.customize.iterate.begin_container.template_parameters"></a><h6>
<a name="id995940"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.template_parameters">Template
parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Description
</p>
</th>
<th>
<p>
Default
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Container</span></code>
</p>
</td>
<td>
<p>
The type, <code class="computeroutput"><span class="identifier">Container</span></code>
for which the iterator pointing to the first element has to be
returned
</p>
</td>
<td>
<p>
none
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Enable</span></code>
</p>
</td>
<td>
<p>
Helper template parameter usable to selectively enable or disable
certain specializations of <code class="computeroutput"><span class="identifier">begin_container</span></code>
utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code>
or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</span></code>).
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.iterate.begin_container.notation"></a><h6>
<a name="id996105"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.notation">Notation</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="computeroutput"><span class="identifier">C</span></code></span></dt>
<dd><p>
A container type the begin iterator needs to be returned for.
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">c</span></code></span></dt>
<dd><p>
An instance of a container, <code class="computeroutput"><span class="identifier">C</span></code>.
</p></dd>
</dl>
</div>
<a name="spirit.advanced.customize.iterate.begin_container.expression_semantics"></a><h6>
<a name="id996170"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.expression_semantics">Expression
Semantics</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">begin_container</span><span class="special"><</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">call</span><span class="special">(</span><span class="identifier">c</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
Return the iterator usable to dereference the first element of
the given container, <code class="computeroutput"><span class="identifier">c</span></code>.
The type of the returned iterator is expected to be the same
as the type returned by the customization point <a class="link" href="container_iterator.html" title="Determine the Type of the Iterator of a Container (Karma)"><code class="computeroutput"><span class="identifier">container_iterator</span></code></a>.
</p>
</td>
</tr></tbody>
</table></div>
<p>
The returned instance conceptually needs to be equivalent to a standard
forward iterator. But it does not have to expose the standardized interface.
If this customization point is implemented for a certain container type,
all related customization points need to be implemented as well (see
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.related_attribute_customization_points">Related
Attribute Customization Points</a> below). This encapsulates the specific
iterator interface required for a given type. The minimal requirements
for a type to be exposed as an iterator in this context are:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
it needs to be comparable for equality (see <a class="link" href="compare_iterators.html" title="Compare two Iterator pointing into a Container Attribute for Equality"><code class="computeroutput"><span class="identifier">compare_iterators</span></code></a>),
</li>
<li class="listitem">
it needs to be incrementable (see <a class="link" href="next_iterator.html" title="Increment the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">next_iterator</span></code></a>),
</li>
<li class="listitem">
it needs to be dereferencible (see <a class="link" href="deref_iterator.html" title="Dereference the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">deref_iterator</span></code></a>).
</li>
</ul></div>
<a name="spirit.advanced.customize.iterate.begin_container.predefined_specializations"></a><h6>
<a name="id996336"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.predefined_specializations">Predefined
Specializations</a>
</h6>
<p>
<a href="http://spirit.sourceforge.net" target="_top">Spirit</a> predefines
specializations of this customization point for several types. The following
table lists those types together with the types returned by the embedded
typedef <code class="computeroutput"><span class="identifier">type</span></code>:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Template Parameters
</p>
</th>
<th>
<p>
Value
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span></code>
</p>
</td>
<td>
<p>
Returns <code class="computeroutput"><span class="identifier">c</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span> <span class="keyword">const</span></code>
</p>
</td>
<td>
<p>
Returns <code class="computeroutput"><span class="identifier">c</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">unused_type</span></code>
</p>
</td>
<td>
<p>
Returns <code class="computeroutput"><span class="special">&</span><span class="identifier">unused</span></code>.
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.iterate.begin_container.when_to_implement"></a><h6>
<a name="id996523"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.when_to_implement">When
to implement</a>
</h6>
<p>
The customization point <code class="computeroutput"><span class="identifier">begin_container</span></code>
needs to be implemented for a specific type whenever this type is to
be used as an attribute in place of a STL container. It is applicable
for generators (<span class="emphasis"><em>Spirit.Karma</em></span>) only. As a rule of
thumb: it has to be implemented whenever a certain type is to be passed
as an attribute to a generator normally exposing a STL container, <code class="computeroutput"><span class="identifier">C</span></code> and if the type does not expose the
interface of a STL container (i.e. <code class="computeroutput"><span class="identifier">is_container</span><span class="special"><</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code>
would normally return <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>).
</p>
<a name="spirit.advanced.customize.iterate.begin_container.related_attribute_customization_points"></a><h6>
<a name="id996594"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.related_attribute_customization_points">Related
Attribute Customization Points</a>
</h6>
<p>
If this customization point is implemented, the following other customization
points might need to be implemented as well.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
When to implement
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="../is_container.html" title="Determine if a Type Should be Treated as a Container (Qi and Karma)"><code class="computeroutput"><span class="identifier">is_container</span></code></a>
</p>
</td>
<td>
<p>
Needs to be implemented whenever a type is to be used as a container
attribute in <span class="emphasis"><em>Karma</em></span>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="container_iterator.html" title="Determine the Type of the Iterator of a Container (Karma)"><code class="computeroutput"><span class="identifier">container_iterator</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="begin_container.html" title="Get the Iterator pointing to the Begin of a Container Attribute"><code class="computeroutput"><span class="identifier">begin_container</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="end_container.html" title="Get the Iterator pointing to the End of a Container Attribute"><code class="computeroutput"><span class="identifier">end_container</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="deref_iterator.html" title="Dereference the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">deref_iterator</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="next_iterator.html" title="Increment the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">next_iterator</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="compare_iterators.html" title="Compare two Iterator pointing into a Container Attribute for Equality"><code class="computeroutput"><span class="identifier">compare_iterators</span></code></a>
</p>
</td>
<td>
<p>
Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="Lists (a % b)">List
(<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star (*a)">Kleene (unary
<code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Directive (repeat[])">Repeat</a>.
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.iterate.begin_container.example"></a><h6>
<a name="id997081"></a>
<a class="link" href="begin_container.html#spirit.advanced.customize.iterate.begin_container.example">Example</a>
</h6>
<p>
For examples of how to use the customization point <code class="computeroutput"><span class="identifier">begin_container</span></code>
please see here: <a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.example">embedded_container_example</a>,
<a class="link" href="next_iterator.html#spirit.advanced.customize.iterate.next_iterator.example">use_as_container</a>,
and <a class="link" href="deref_iterator.html#spirit.advanced.customize.iterate.deref_iterator.example">counter_example</a>.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2010 Joel de Guzman, Hartmut Kaiser<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
</tr></table>
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