From cppreference.com
Defined in header
inlineconstexpr/* unspecified */counted=/* unspecified */;(since C++20)Call signature
template<classIterator,classDifferenceType>requires/* see below */constexpr/*span-or-subrange*/counted(Iterator&&it,DifferenceType&&count);(since C++20)A counted view presents a
of the elements of the counted range[i, n) for some iterator i and non-negative integer n.
A counted range [i, n) is the n elements starting with the element pointed to by i and up to but not including the element, if any, pointed to by the result of n applications of ++i.
If n==0, the counted range is valid and empty. Otherwise, the counted range is only valid if n is positive, i is dereferenceable, and [++i, --n) is a valid counted range.
Formally, if it and count are expressions, T is std::decay_t<decltype((it))>, and D is std::iter_difference_t<T>, then
if T models
and decltype((count)) models std::convertible_to<D>, if T models
, then views::counted(it,count) is
to std::span(std::to_address(it),static_cast<std::size_t>(static_cast<D>(count))),
otherwise, if T models
, then views::counted(it,count) is
to ranges::subrange(it,it+static_cast<D>(count)),
otherwise, views::counted(it,count) is
to ranges::subrange(std::counted_iterator(it,count),std::default_sentinel).
Otherwise, views::counted(it,count) is ill-formed.Customization point objects
The name views::counted denotes a customization point object, which is a const
of a
class type. See
for details.
Notes
views::counted does not check if the range is long enough to provide all count elements: use views::take if that check is necessary.
Example
Run this code
#include<iostream>#include<ranges>intmain(){constinta[]{1,2,3,4,5,6,7};for(inti:std::views::counted(a,3))std::cout<<i<<' ';std::cout<<'\n';constautoil={1,2,3,4,5};for(inti:std::views::counted(il.begin()+1,3))std::cout<<i<<' ';std::cout<<'\n';}Output:
1 2 3 2 3 4 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++20 implicit conversion from an integer-class type to std::size_t might be invalid made explicit See also