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<title>Restricted Pointers (Using the GNU Compiler Collection (GCC))</title>

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<a name="Restricting-Pointer-Aliasing"></a>
<h3 class="section">7.2 Restricting Pointer Aliasing</h3>
<a name="index-restricted-pointers"></a>
<a name="index-restricted-references"></a>
<a name="index-restricted-this-pointer"></a>

<p>As with the C front end, G++ understands the C99 feature of restricted pointers,
specified with the <code>__restrict__</code>, or <code>__restrict</code> type
qualifier.  Because you cannot compile C++ by specifying the <samp>-std=c99</samp>
language flag, <code>restrict</code> is not a keyword in C++.
</p>
<p>In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the local
context.
</p>
<div class="smallexample">
<pre class="smallexample">void fn (int *__restrict__ rptr, int &amp;__restrict__ rref)
{
  /* <span class="roman">&hellip;</span> */
}
</pre></div>

<p>In the body of <code>fn</code>, <var>rptr</var> points to an unaliased integer and
<var>rref</var> refers to a (different) unaliased integer.
</p>
<p>You may also specify whether a member function&rsquo;s <var>this</var> pointer is
unaliased by using <code>__restrict__</code> as a member function qualifier.
</p>
<div class="smallexample">
<pre class="smallexample">void T::fn () __restrict__
{
  /* <span class="roman">&hellip;</span> */
}
</pre></div>

<p>Within the body of <code>T::fn</code>, <var>this</var> has the effective
definition <code>T *__restrict__ const this</code>.  Notice that the
interpretation of a <code>__restrict__</code> member function qualifier is
different to that of <code>const</code> or <code>volatile</code> qualifier, in that it
is applied to the pointer rather than the object.  This is consistent with
other compilers that implement restricted pointers.
</p>
<p>As with all outermost parameter qualifiers, <code>__restrict__</code> is
ignored in function definition matching.  This means you only need to
specify <code>__restrict__</code> in a function definition, rather than
in a function prototype as well.
</p>


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