NAME¶

std::ranges::subrange::advance - std::ranges::subrange::advance

Synopsis¶

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.

Parameters¶

n - number of maximal increments of the iterator

Return value¶

*this

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.

Notes¶

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

Example¶

// Run this code

#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));
}

Output:¶

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

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 < corrected
0

See also¶

next obtains a copy of the subrange with its iterator advanced by a given
(C++20) distance
(public member function)
prev obtains a copy of the subrange with its iterator decremented by a
(C++20) given distance
(public member function)
advance advances an iterator by given distance
(function template)
ranges::advance advances an iterator by given distance or to a given bound
(C++20) (niebloid)