A counted view presents aview of the elements of thecounted range[i, n) for some iteratori and non-negative integern.

A counted range[i, n) is then elements starting with the element pointed to byi and up to but not including the element, if any, pointed to by the result ofn applications of++i.

Ifn==0, the counted range is valid and empty. Otherwise, the counted range is only valid ifn is positive,i is dereferenceable, and[++i, --n) is a valid counted range.

Formally, ifit andcount are expressions,T isstd::decay_t<decltype((it))>, andD isstd::iter_difference_t<T>, then

ifT modelsinput_or_output_iterator anddecltype((count)) modelsstd::convertible_to<D>,

• ifT modelscontiguous_iterator, thenviews::counted(it, count) isexpression-equivalent tostd::span(std::to_address(it),static_cast<std::size_t>(static_cast<D>(count))),
• otherwise, ifT modelsrandom_access_iterator, thenviews::counted(it, count) isexpression-equivalent toranges::subrange(it, it+static_cast<D>(count)),
• otherwise,views::counted(it, count) isexpression-equivalent toranges::subrange(std::counted_iterator(it, count),std::default_sentinel).

Otherwise,views::counted(it, count) is ill-formed.

Customization point objects

The nameviews::counted denotes acustomization point object, which is a constfunction object of aliteralsemiregular class type. SeeCustomizationPointObject for details.

[edit]Notes

views::counted does not check if the range is long enough to provide allcount elements: useviews::take if that check is necessary.

[edit]Example

#include <iostream>#include <ranges> int main(){constint a[]{1,2,3,4,5,6,7};for(int i: std::views::counted(a,3))std::cout<< i<<' ';std::cout<<'\n'; constauto il={1,2,3,4,5};for(int i: std::views::counted(il.begin()+1,3))std::cout<< i<<' ';std::cout<<'\n';}

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[edit]Defect reports

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

[edit]See also

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