std::ranges::iota_view<W, Bound>::size

constexpr auto size() const
    requires (std::same_as<W, Bound> && /*advanceable*/<W>) ||
             (/*is-integer-like*/<W> && /*is-integer-like*/<Bound>) ||
             std::sized_sentinel_for<Bound, W>;

Returns the size of the view if the view is bounded.

For the definitions of /*advanceable*/ and /*is-integer-like*/, see advanceable and is-integer-like respectively.

Return value

If any of W and Bound is not a integer-like type, returns to-unsigned-like (bound_ - value_ ).

Otherwise, returns (value_ <0)?
    (
        (bound_ <0)?
            to-unsigned-like (-value_ )- to-unsigned-like (-bound_ ):
            to-unsigned-like (bound_ )+ to-unsigned-like (-value_ )
    ):
    to-unsigned-like (bound_ )- to-unsigned-like (value_ ) .

Example

#include <cassert>
#include <ranges>

int main()
{
    unsigned initial_value{1}, bound{5};
    auto i{std::views::iota(initial_value, bound)};
    assert(i.size() == bound - initial_value and i.size() == 4);
    
    auto u{std::views::iota(8)};
    // assert(u.size()); // Error: size() is not present since “u” is unbounded
}

Defect reports

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

See also