# deduction guides for `std::basic_string_view`

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< cpp‎ | string‎ | basic string view

Defined in header `<string_view>` |  |
template< class It, class End > basic_string_view( It, End ) -> basic_string_view< std::iter_value_t <It>>; | (1) | (since C++20)
template< class R > basic_string_view( R&& ) -> basic_string_view< ranges::range_value_t <R>>; | (2) | (since C++23)

These deduction guides are provided for std::basic_string_view.

1) This deduction guide allow the character type to be deduced from the iterator-sentinel pair. This overload participates in overload resolution only if `It` satisfies `contiguous_iterator` and `End` satisfies `sized_sentinel_for` for `It`.
2) This deduction guide allow the character type to be deduced from the range. This overload participates in overload resolution only if `R` satisfies `contiguous_range`.

### Example

Run this code

    #include <array>
    #include <iostream>
    #include <string_view>

    int main()
    {
        std::array a1{'n', 'u', 'c', 'l', 'e', 'o', 'n', 's', ':', '\n'};
        std::basic_string_view s1(a1.cbegin(), a1.cend()); // deduction: CharT -> char
        static_assert(std::is_same_v<decltype(s1)::value_type, char>);
        std::cout << s1;

        std::array a2{L'p', L'r', L'o', L't', L'o', L'n', L's', L'\n'};
        std::basic_string_view s2(a2.cbegin(), a2.cend()); // deduction: CharT -> wchar_t
        static_assert(std::is_same_v<decltype(s2)::value_type, wchar_t>);
        std::wcout << s2;

        std::array<long, 9> a3{'n', 'e', 'u', 't', 'r', 'o', 'n', 's', '\n'};
        std::basic_string_view s3(a3.cbegin(), a3.cend()); // deduction: CharT -> long
        static_assert(std::is_same_v<decltype(s3)::value_type, long>);
        for (const auto e : s3)
            std::cout << static_cast<char>(e);
    }

Output:

    nucleons:
    protons
    neutrons

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