23 Iterators library [iterators]

23.4 Iterator primitives [iterator.primitives]

23.4.3 Range iterator operations [range.iter.ops]

23.4.3.1 ranges​::​advance [range.iter.op.advance]

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template<input_­or_­output_­iterator I> constexpr void ranges::advance(I& i, iter_difference_t<I> n);
1
#
Preconditions: If I does not model bidirectional_­iterator, n is not negative.
2
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Effects:
  • (2.1)
    If I models random_­access_­iterator, equivalent to i += n.
  • (2.2)
    Otherwise, if n is non-negative, increments i by n.
  • (2.3)
    Otherwise, decrements i by -n.
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template<input_­or_­output_­iterator I, sentinel_­for<I> S> constexpr void ranges::advance(I& i, S bound);
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Preconditions: [i, bound) denotes a range.
4
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Effects:
  • (4.1)
    If I and S model assignable_­from<I&, S>, equivalent to i = std​::​move(bound).
  • (4.2)
    Otherwise, if S and I model sized_­sentinel_­for<S, I>, equivalent to ranges​::​advance(i, bound - i).
  • (4.3)
    Otherwise, while bool(i != bound) is true, increments i.
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template<input_­or_­output_­iterator I, sentinel_­for<I> S> constexpr iter_difference_t<I> ranges::advance(I& i, iter_difference_t<I> n, S bound);
5
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Preconditions: If n > 0, [i, bound) denotes a range.
If n == 0, [i, bound) or [bound, i) denotes a range.
If n < 0, [bound, i) denotes a range, I models bidirectional_­iterator, and I and S model same_­as<I, S>.
6
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Effects:
  • (6.1)
    If S and I model sized_­sentinel_­for<S, I>:
    • (6.1.1)
      If ​, equivalent to ranges​::​advance(i, bound).
    • (6.1.2)
      Otherwise, equivalent to ranges​::​advance(i, n).
  • (6.2)
    Otherwise,
    • (6.2.1)
      if n is non-negative, while bool(i != bound) is true, increments i but at most n times.
    • (6.2.2)
      Otherwise, while bool(i != bound) is true, decrements i but at most -n times.
7
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Returns: n - M, where M is the difference between the ending and starting positions of i.