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<h2><a name="at" id="at">at</a></h2>
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<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="co2">#include <vector></span>
TYPE<span class="sy0">&</span> at<span class="br0">(</span> size_type loc <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">const</span> TYPE<span class="sy0">&</span> at<span class="br0">(</span> size_type loc <span class="br0">)</span> <span class="kw4">const</span><span class="sy0">;</span></pre>
<p>
The at() function returns a reference to the element in the vector at
index loc. The at() function is safer than the <a href="../../stl/vector/operator.html" class="wikilink1" title="stl:vector:vector_operators">[]
operator</a>, because it won't let you reference items outside the bounds
of the vector.
</p>
<p>
For example, consider the following code:
</p>
<pre class="c code c++" style="font-family:monospace;"> vector<span class="sy0"><</span>int<span class="sy0">></span> v<span class="br0">(</span> 5<span class="sy0">,</span> 1 <span class="br0">)</span><span class="sy0">;</span>
<span class="kw1">for</span><span class="br0">(</span> <span class="kw4">int</span> i <span class="sy0">=</span> <span class="nu0">0</span><span class="sy0">;</span> i <span class="sy0"><</span> <span class="nu0">10</span><span class="sy0">;</span> i<span class="sy0">++</span> <span class="br0">)</span> <span class="br0">{</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"Element "</span> <span class="sy0"><<</span> i <span class="sy0"><<</span> <span class="st0">" is "</span> <span class="sy0"><<</span> v<span class="br0">[</span>i<span class="br0">]</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<span class="br0">}</span></pre>
<p>
This code overruns the end of the vector, producing potentially dangerous
results. The following code would be much safer:
</p>
<pre class="c code c++" style="font-family:monospace;"> vector<span class="sy0"><</span>int<span class="sy0">></span> v<span class="br0">(</span> 5<span class="sy0">,</span> 1 <span class="br0">)</span><span class="sy0">;</span>
<span class="kw1">for</span><span class="br0">(</span> <span class="kw4">int</span> i <span class="sy0">=</span> <span class="nu0">0</span><span class="sy0">;</span> i <span class="sy0"><</span> <span class="nu0">10</span><span class="sy0">;</span> i<span class="sy0">++</span> <span class="br0">)</span> <span class="br0">{</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"Element "</span> <span class="sy0"><<</span> i <span class="sy0"><<</span> <span class="st0">" is "</span> <span class="sy0"><<</span> v.<span class="me1">at</span><span class="br0">(</span>i<span class="br0">)</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<span class="br0">}</span></pre>
<p>
Instead of attempting to read garbage values from memory, the at() function
will realize that it is about to overrun the vector and will throw an
exception (out_of_range).
</p>
<p>
Related Topics: <a href="../../stl/vector/operator.html" class="wikilink1" title="stl:vector:vector_operators">[] operator</a>
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