NAME

std::ranges::next - std::ranges::next

Synopsis

Defined in header <iterator>
Call signature
template< std::input_or_output_iterator I > (1) (since C++20)
constexpr I next( I i );
template< std::input_or_output_iterator I > (2) (since C++20)
constexpr I next( I i, std::iter_difference_t<I> n );
template< std::input_or_output_iterator I, std::sentinel_for<I> S
> (3) (since C++20)
constexpr I next( I i, S bound );
template< std::input_or_output_iterator I, std::sentinel_for<I> S
> (4) (since C++20)
constexpr I next( I i, std::iter_difference_t<I> n, S bound );

Return the nth successor of iterator i.

The function-like entities described on this page are niebloids, that is:

* Explicit template argument lists may not be specified when calling any of them.
* None of them is visible to argument-dependent lookup.
* When one of them is found by normal unqualified lookup for the name to the left
of the function-call operator, it inhibits argument-dependent lookup.

In practice, they may be implemented as function objects, or with special compiler
extensions.

Parameters

i - an iterator
n - number of elements to advance
bound - sentinel denoting the end of the range i points to

Return value

1) The successor of iterator i
2) The nth successor of iterator i
3) The first iterator equivalent to bound
4) The nth successor of iterator i, or the first iterator equivalent to bound,
whichever is first.

Complexity

1) Constant.
2) Constant if I models std::random_access_iterator; otherwise linear.
3) Constant if I and S models both std::random_access_iterator<I> and
std::sized_sentinel_for<S, I>, or if I and S models std::assignable_from<I&, S>;
otherwise linear.
4) Constant if I and S models both std::random_access_iterator<I> and
std::sized_sentinel_for<S, I>; otherwise linear.

Possible implementation

struct next_fn {
template<std::input_or_output_iterator I>
constexpr I operator()(I i) const
{
++i;
return i;
}

template<std::input_or_output_iterator I>
constexpr I operator()(I i, std::iter_difference_t<I> n) const
{
ranges::advance(i, n);
return i;
}

template<std::input_or_output_iterator I, std::sentinel_for<I> S>
constexpr I operator()(I i, S bound) const
{
ranges::advance(i, bound);
return i;
}

template<std::input_or_output_iterator I, std::sentinel_for<I> S>
constexpr I operator()(I i, std::iter_difference_t<I> n, S bound) const
{
ranges::advance(i, n, bound);
return i;
}
};

inline constexpr auto next = next_fn();

Notes

Although the expression ++x.begin() often compiles, it is not guaranteed to do so:
x.begin() is an rvalue expression, and there is no requirement that specifies that
increment of an rvalue is guaranteed to work. In particular, when iterators are
implemented as pointers or its operator++ is lvalue-ref-qualified, ++x.begin() does
not compile, while ranges::next(x.begin()) does.

Example

// Run this code

#include <iomanip>
#include <iostream>
#include <iterator>
#include <vector>

int main()
{
std::cout << std::boolalpha;
std::vector<int> v{ 3, 1, 4 };
{
auto n = std::ranges::next(v.begin());
std::cout << *n << '\n';
}
{
auto n = std::ranges::next(v.begin(), 2);
std::cout << *n << '\n';
}
{
auto n = std::ranges::next(v.begin(), v.end());
std::cout << (n == v.end()) << '\n';
}
{
auto n = std::ranges::next(v.begin(), 42, v.end());
std::cout << (n == v.end()) << '\n';
}
}

Output:

1
4
true
true

See also

ranges::prev decrement an iterator by a given distance or to a bound
(C++20) (niebloid)
ranges::advance advances an iterator by given distance or to a given bound
(C++20) (niebloid)
next increment an iterator
(C++11) (function template)