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(gcc-300.info)Restricted Pointers

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Restricting Pointer Aliasing
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   As with gcc, g++ understands the C99 feature of restricted pointers,
specified with the `__restrict__', or `__restrict' type qualifier.
Because you cannot compile C++ by specifying the `-std=c99' language
flag, `restrict' is not a keyword in C++.

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

     void fn (int *__restrict__ rptr, int &__restrict__ rref)
     {
       ...
     }

In the body of `fn', RPTR points to an unaliased integer and RREF
refers to a (different) unaliased integer.

   You may also specify whether a member function's THIS pointer is
unaliased by using `__restrict__' as a member function qualifier.

     void T::fn () __restrict__
     {
       ...
     }

Within the body of `T::fn', THIS will have the effective definition `T
*__restrict__ const this'.  Notice that the interpretation of a
`__restrict__' member function qualifier is different to that of
`const' or `volatile' qualifier, in that it is applied to the pointer
rather than the object.  This is consistent with other compilers which
implement restricted pointers.

   As with all outermost parameter qualifiers, `__restrict__' is
ignored in function definition matching.  This means you only need to
specify `__restrict__' in a function definition, rather than in a
function prototype as well.