23 Iterators library [iterators]

23.3 Iterator requirements [iterator.requirements]

23.3.4 Iterator concepts [iterator.concepts]

23.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]

1
#
The random_­access_­iterator concept adds support for constant-time advancement with +=, +, -=, and -, as well as the computation of distance in constant time with -.
Random access iterators also support array notation via subscripting.
template<class I> concept random_­access_­iterator = bidirectional_­iterator<I> && derived_­from<ITER_CONCEPT(I), random_access_iterator_tag> && totally_­ordered<I> && sized_­sentinel_­for<I, I> && requires(I i, const I j, const iter_difference_t<I> n) { { i += n } -> same_­as<I&>; { j + n } -> same_­as<I>; { n + j } -> same_­as<I>; { i -= n } -> same_­as<I&>; { j - n } -> same_­as<I>; { j[n] } -> same_­as<iter_reference_t<I>>; };
2
#
Let a and b be valid iterators of type I such that b is reachable from a after n applications of ++a, let D be iter_­difference_­t<I>, and let n denote a value of type D.
I models random_­access_­iterator only if
  • (2.1)
    (a += n) is equal to b.
  • (2.2)
    addressof(a += n) is equal to addressof(a).
  • (2.3)
    (a + n) is equal to (a += n).
  • (2.4)
    For any two positive values x and y of type D, if (a + D(x + y)) is valid, then (a + D(x + y)) is equal to ((a + x) + y).
  • (2.5)
    (a + D(0)) is equal to a.
  • (2.6)
    If (a + D(n - 1)) is valid, then (a + n) is equal to [](I c){ return ++c; }(a + D(n - 1)).
  • (2.7)
    (b += D(-n)) is equal to a.
  • (2.8)
    (b -= n) is equal to a.
  • (2.9)
    addressof(b -= n) is equal to addressof(b).
  • (2.10)
    (b - n) is equal to (b -= n).
  • (2.11)
    If b is dereferenceable, then a[n] is valid and is equal to *b.
  • (2.12)
    bool(a <= b) is true.