The keywords __restrict and __restrict__ are supported as synonyms for restrict and are always available.

You can specify --restrict to allow the use of the restrict keyword in C90 or C++.

The declaration of intent is effectively a promise to the compiler that, if broken, results in undefined behavior.

The following example shows use of the restrict keyword applied to function parameter arrays.

void copy_array(int n, int *restrict a, int *restrict b)
{
    while (n-- > 0)
        *a++ = *b++;
}

The following example shows use of the restrict keyword applied to different pointers that exist in the form of local variables.

void copy_bytes(int n, int *a, int *b)
{
  int *restrict x;
  int *restrict y;

    x = a;
    y = b;

    while (n-- > 0)
     *q++ = *s++;
}