std::ranges::next

 

C++

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Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

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

Return the n^th successor of iterator i.

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

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

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 n^th successor of iterator i.

3) The first iterator equivalent to bound.

4) The n^th 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 <cassert>
#include <iterator>
 
int main() 
{
    auto v = {3, 1, 4};
    {
        auto n = std::ranges::next(v.begin());
        assert(*n == 1);
    }
    {
        auto n = std::ranges::next(v.begin(), 2);
        assert(*n == 4);
    }
    {
        auto n = std::ranges::next(v.begin(), v.end());
        assert(n == v.end());
    }
    {
        auto n = std::ranges::next(v.begin(), 42, v.end());
        assert(n == v.end());
    }
}

See also

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