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boost_fusion/doc/html/fusion/sequences/intrinsics/functions/at_c.html
Tobias Schwinger ca6f831b96 adds documentation for functional module 
[SVN r36959]
2007-02-15 23:11:24 +00:00

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<div class="titlepage"><div><div><h5 class="title">
<a name="fusion.sequences.intrinsics.functions.at_c"></a><a href="at_c.html" title="at_c">at_c</a></h5></div></div></div>
<a name="fusion.sequences.intrinsics.functions.at_c.description"></a><h6>
<a name="id1009079"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.description">Description</a>
</h6>
<p>
Returns the N-th element from the beginning of the sequence.
</p>
<a name="fusion.sequences.intrinsics.functions.at_c.synopsis"></a><h6>
<a name="id1009108"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.synopsis">Synopsis</a>
</h6>
<pre class="programlisting">
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_c</span></code></a><span class="special">&lt;</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">at_c</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&amp;</span> <span class="identifier">seq</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_c</span></code></a><span class="special">&lt;</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">at_c</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">seq</span><span class="special">);</span>
</pre>
<a name="fusion.sequences.intrinsics.functions.at_c.parameters"></a><h6>
<a name="id1009402"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput"><span class="identifier">seq</span></code></td>
<td>Model
of <a href="../../concepts/random_access_sequence.html" title="Random
Access Sequence">Random
Access Sequence</a>
</td>
<td>The sequence we wish to investigate.</td>
</tr>
<tr>
<td><code class="computeroutput"><span class="identifier">N</span></code></td>
<td>An
integral constant</td>
<td>An index from the beginning of
the sequence.</td>
</tr>
</tbody>
</table></div>
<a name="fusion.sequences.intrinsics.functions.at_c.expression_semantics"></a><h6>
<a name="id1009499"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.expression_semantics">Expression
Semantics</a>
</h6>
<pre class="programlisting">
<span class="identifier">at_c</span><span class="special">&lt;</span><span class="identifier">N</span><span class="special">&gt;(</span><span class="identifier">seq</span><span class="special">);</span>
</pre>
<p>
<span class="bold"><strong>Return type</strong></span>: Returns a reference to
the N-th element from the beginning of the sequence <code class="computeroutput"><span class="identifier">seq</span></code>
if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and
<code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
<span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code>
is the N-th element from the beginning of the sequence, is a valid expression.
Else, returns a type convertable to the N-th element from the beginning
of the sequence.
</p>
<p>
<span class="bold"><strong>Precondition</strong></span>: <code class="computeroutput"><span class="number">0</span>
<span class="special">&lt;=</span> <span class="identifier">N</span>
<span class="special">&lt;</span> <a href="size.html" title="size"><code class="computeroutput"><span class="identifier">size</span></code></a><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>
</p>
<p>
<span class="bold"><strong>Semantics</strong></span>: Equivalent to
</p>
<pre class="programlisting">
<a href="../../../iterators/functions/deref.html" title="deref"><code class="computeroutput"><span class="identifier">deref</span></code></a><span class="special">(</span><a href="../../../iterators/functions/advance.html" title="advance"><code class="computeroutput"><span class="identifier">advance</span></code></a><span class="special">&lt;</span><span class="identifier">N</span><span class="special">&gt;(</span><a href="begin.html" title="begin"><code class="computeroutput"><span class="identifier">begin</span></code></a><span class="special">(</span><span class="identifier">s</span><span class="special">)))</span>
</pre>
<a name="fusion.sequences.intrinsics.functions.at_c.header"></a><h6>
<a name="id1009762"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.header">Header</a>
</h6>
<pre class="programlisting">
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">sequence</span><span class="special">/</span><span class="identifier">intrinsic</span><span class="special">/</span><span class="identifier">at_c</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="fusion.sequences.intrinsics.functions.at_c.example"></a><h6>
<a name="id1009855"></a>
<a href="at_c.html#fusion.sequences.intrinsics.functions.at_c.example">Example</a>
</h6>
<pre class="programlisting">
<a href="../../containers/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">at_c</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
</pre>
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