std::ranges::distance - cppreference.com (original) (raw)

Defined in header
Call signature
template< class I, std::sentinel_for<I> S > requires (<S, I>) constexpr std::iter_difference_t<I> distance( I first, S last );	(1)	(since C++20)
template< class I, std::sized_sentinel_for<std::decay_t<I>> S > constexpr std::iter_difference_t<std::decay_t<I>> distance( I&& first, S last );	(2)	(since C++20)
template< ranges::range R > constexpr ranges::range_difference_t<R> distance( R&& r );	(3)	(since C++20)

1,2) Returns the number of hops from first to last.

1. Returns the size of r as a signed integer.

The function-like entities described on this page are algorithm function objects (informally known as 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Return value

1. The number of increments needed to go from first to last.

2. last - static_cast<const std::decay_t<I>&>(first).

[edit] Complexity

1. Linear.

2. Constant.

[edit] Possible implementation

[edit] Example

#include #include #include #include   int main() { std::vector v{3, 1, 4}; assert(std::ranges::distance(v.begin(), v.end()) == 3); assert(std::ranges::distance(v.end(), v.begin()) == -3); assert(std::ranges::distance(v) == 3);   std::forward_list l{2, 7, 1}; // auto size = std::ranges::size(l); // error: not a sizable range auto size = std::ranges::distance(l); // OK, but aware O(N) complexity assert(size == 3); }

[edit] Defect reports

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

[edit] See also