As with the C front end, 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 has 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 that 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.