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    <p>Element access time in a typical implementation of a <code>std::vector</code> is the same as element access time in an ordinary array available through a <em>pointer object</em> (i.e. a <em>run-time</em> pointer value)</p> <pre><code>std::vector&lt;int&gt; v; int *pa; ... v[i]; pa[i]; // Both have the same access time </code></pre> <p>However, the access time to an element of an array available as an <em>array object</em> is better than both of the above accesses (equivalent to access through a <em>compile-time</em> pointer value)</p> <pre><code>int a[100]; ... a[i]; // Faster than both of the above </code></pre> <p>For example, a typical read access to an <code>int</code> array available through a run-time pointer value will look as follows in the compiled code on x86 platform</p> <pre><code>// pa[i] mov ecx, pa // read pointer value from memory mov eax, i mov &lt;result&gt;, dword ptr [ecx + eax * 4] </code></pre> <p>Access to vector element will look pretty much the same.</p> <p>A typical access to a local <code>int</code> array available as an array object will look as follows</p> <pre><code>// a[i] mov eax, i mov &lt;result&gt;, dword ptr [esp + &lt;offset constant&gt; + eax * 4] </code></pre> <p>A typical access to a global <code>int</code> array available as an array object will look as follows</p> <pre><code>// a[i] mov eax, i mov &lt;result&gt;, dword ptr [&lt;absolute address constant&gt; + eax * 4] </code></pre> <p>The difference in perfromance arises from that extra <code>mov</code> instruction in the first variant, which has to make an extra memory access.</p> <p>However, the difference is negligible. And it is easily optimized to the point of being exactly the same in multiple-access context (by loading the target address in a register). </p> <p>So the statement about "arrays being a bit faster" is correct in narrow case when the array is accessible directly through the array object, not through a pointer object. But the practical value of that difference is virtually nothing.</p>
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    1. COWhat are you talking about? You should really illustrate this with some kind of machine-level description of what would be different.
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    2. CO@Potatoswatter: I just added a machine level description.
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    3. COOK. But that presumes the array is on the stack, not in a data structure, passed by reference, or in namespace scope. It also presumes the `vector` base pointer isn't promoted to a register, which is to be expected inside a loop.
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