< cpp‎ | ranges‎ | subrange
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constexpr subrange& advance( std::iter_difference_t<I> n );
(since C++20)

If n >= 0, increments the stored iterator for n times, or until it is equal to the stored sentinel, whichever comes first. Otherwise, decrements the stored iterator for -n times.

The stored size, if any, is adjusted accordingly (increased by -n if n < 0, decreased by m otherwise, where m is the number of increments actually applied to the iterator).

The behavior is undefined if

  • I does not model bidirectional_iterator and n < 0, or
  • the stored iterator is decremented after becoming a non-decrementable value.


[edit] Parameters

n - number of maximal increments of the iterator

[edit] Return value


[edit] Complexity

Generally min(n, size()) increments or -n decrements on the iterator, when n >= 0 or n < 0 respectively.

Constant if I models random_access_iterator, and either n < 0 or std::sized_sentinel_for<S, I> is modeled.

[edit] Notes

The stored size presents if and only if K == ranges::subrange_kind::sized but std::sized_sentinel_for<S, I> is not satisfied.

[edit] Example

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <ranges>
void print(auto name, auto const sub) {
    std::cout << name << ".size() == " << sub.size() << "; { ";
    std::ranges::for_each(sub, [](int x) { std::cout << x << ' '; });
    std::cout << "}\n";
int main()
    std::array arr{1,2,3,4,5,6,7};
    std::ranges::subrange sub{ std::next(arr.begin()), std::prev(arr.end()) };
    print("1) sub", sub);
    print("2) sub", sub.advance(3));
    print("3) sub", sub.advance(-2));


1) sub.size() == 5; { 2 3 4 5 6 }
2) sub.size() == 2; { 5 6 }
3) sub.size() == 4; { 3 4 5 6 }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3433 C++20 the specification mishandled the cases when n < 0 corrected

[edit] See also

obtains a copy of the subrange with its iterator advanced by a given distance
(public member function) [edit]
obtains a copy of the subrange with its iterator decremented by a given distance
(public member function) [edit]
advances an iterator by given distance
(function template) [edit]
advances an iterator by given distance or to a given bound
(niebloid) [edit]