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<h3 class="section">7.2 Restricting Pointer Aliasing</h3>

<p><a name="index-restricted-pointers-3163"></a><a name="index-restricted-references-3164"></a><a name="index-restricted-this-pointer-3165"></a>
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><span class="option">-std=c99</span></samp>
language flag, <code>restrict</code> is not a keyword in C++.

 <p>In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the local
context.

<pre class="smallexample">     void fn (int *__restrict__ rptr, int &amp;__restrict__ rref)
     {
       /* <span class="roman">...</span> */
     }
</pre>
 <p class="noindent">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>You may also specify whether a member function's <var>this</var> pointer is
unaliased by using <code>__restrict__</code> as a member function qualifier.

<pre class="smallexample">     void T::fn () __restrict__
     {
       /* <span class="roman">...</span> */
     }
</pre>
 <p class="noindent">Within the body of <code>T::fn</code>, <var>this</var> will have 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 which implement restricted pointers.

 <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.

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