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| <title>Using the GNU Compiler Collection (GCC): Restricted Pointers</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 &__restrict__ rref) |
| { |
| /* <span class="roman">…</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’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">…</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. |
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