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table of contents

std::experimental::ranges::distance(3) | C++ Standard Libary | std::experimental::ranges::distance(3) |

# NAME¶

std::experimental::ranges::distance - std::experimental::ranges::distance

# Synopsis¶

Defined in header <experimental/ranges/iterator>

namespace {

(ranges TS)

constexpr /* unspecified */ distance = /* unspecified */; (customization

point object)

}

Call signature

template< Iterator I, Sentinel<I> S > **(1)**

constexpr ranges::difference_type_t<I> distance(I first, S last);

template< Range R >

constexpr ranges::difference_type_t<ranges::iterator_t<R>>
**(2)**

distance(R&& r);

template< SizedRange R >

constexpr ranges::difference_type_t<ranges::iterator_t<R>>
**(3)**

distance(R&& r);

Returns the distance between first and last, or between the beginning and the
end of

the range r.

1) If SizedSentinel<S, I> is satisfied, equivalent to return last -
first;.

Otherwise, returns the number of increments needed to get from first to last.
If

[first, last) does not denote a range, then I and S must be the same type and
must

model SizedSentinel, and [last, first) must denote a range. Otherwise, the
behavior

is undefined.

2) Equivalent to return ranges::distance(ranges::begin(r), ranges::end(r));

3) Equivalent to return ranges::size(r);

Instantiating overloads (2-3) may be ill-formed if the header

<experimental/ranges/range> is not included before the point of
instantiation.

Customization point objects

The name ranges::distance denotes a customization point object, which is a
function

object of a literal Semiregular class type (denoted, for exposition purposes,
as

DistanceT). All instances of DistanceT are equal. Thus, ranges::distance can
be

copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the
requirements for

arguments to ranges::distance above, DistanceT will satisfy
ranges::Invocable<const

DistanceT, Args...>. Otherwise, no function call operator of DistanceT
participates

in overload resolution.

In every translation unit in which ranges::distance is defined, it refers to
the

same instance of the customization point object. (This means that it can be
used

freely in things like inline functions and function templates without
violating the

one-definition rule.)

# Return value¶

The distance between first and last, or between the beginning and
the end of the

range r.

# Example¶

This section is incomplete

Reason: no example

# See also¶

distance returns the distance between two iterators

*(function template)*

advance advances an iterator by given distance

*(function template)*

next increment an iterator

*(function template)*

prev decrement an iterator

*(function template)*

size obtains the size of a range whose size can be calculated in constant
time

(customization point object)

2022.07.31 | http://cppreference.com |