[string.view.cons]

constexpr basic_string_view() noexcept;

Postconditions: size_ == 0 and data_ == nullptr.

constexpr basic_string_view(const charT* str);

Effects: Constructs a basic_string_view, initializing data_ with str and initializing size_ with traits::length(str).

Complexity:

O (traits::length(str)) .

constexpr basic_string_view(const charT* str, size_type len);

Effects: Constructs a basic_string_view, initializing data_ with str and initializing size_ with len.

template<class It, class End>
  constexpr basic_string_view(It begin, End end);

Effects: Initializes data_ with to_address(begin) and initializes size_ with end - begin.

Throws: When and what end - begin throws.

template<class R>
  constexpr explicit basic_string_view(R&& r);

Constraints:

(12.1)
remove_cvref_t<R> is not the same type as basic_string_view,
(12.2)
R models ranges::contiguous_range and ranges::sized_range,
(12.3)
is_same_v<ranges::range_value_t<R>, charT> is true,
(12.4)
is_convertible_v<R, const charT*> is false, and
(12.5)
d.operator ::std::basic_string_view<charT, traits>() is not a valid expression.

Effects: Initializes data_ with ranges::data(r) and size_ with ranges::size(r).

Throws: Any exception thrown by ranges::data(r) and ranges::size(r).

27 Strings library [strings]