# Standard library header <string_view>

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This header is part of the strings library.

### Classes

basic_string_view (C++17) | read-only string view (class template)
std::string_view | std::basic_string_view <char>
std::u8string_view | std::basic_string_view <char8_t> (C++20)
std::u16string_view | std::basic_string_view <char16_t>
std::u32string_view | std::basic_string_view <char32_t>
std::wstring_view | std::basic_string_view <wchar_t>
std::hash<std::string_view>std::hash<std::wstring_view>std::hash<std::u8string_view>std::hash<std::u16string_view>std::hash<std::u32string_view> (C++17)(C++17)(C++20)(C++17)(C++17) | hash support for string views (class template specialization)

### Functions

operator==operator!=operator<operator>operator<=operator>= | lexicographically compares two string views (function template)
operator<< | performs stream output on string views (function template)

### Synopsis

    namespace std {

    // class template basic_string_view
    template<class charT, class traits = char_traits<charT>>
    class basic_string_view;

    // non-member comparison functions
    template<class charT, class traits>
    constexpr bool operator==(basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    template<class charT, class traits>
    constexpr bool operator!=(basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    template<class charT, class traits>
    constexpr bool operator< (basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    template<class charT, class traits>
    constexpr bool operator> (basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    template<class charT, class traits>
    constexpr bool operator<=(basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    template<class charT, class traits>
    constexpr bool operator>=(basic_string_view<charT, traits> x,
                              basic_string_view<charT, traits> y) noexcept;
    /* sufficient additional overloads of comparison functions */

    // inserters and extractors
    template<class charT, class traits>
    basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, basic_string_view<charT, traits> str);

    // basic_string_view typedef names
    using string_view    = basic_string_view<char>;
    using u8string_view  = basic_string_view<char8_t>;
    using u16string_view = basic_string_view<char16_t>;
    using u32string_view = basic_string_view<char32_t>;
    using wstring_view   = basic_string_view<wchar_t>;

    // hash support
    template<class T> struct hash;
    template<> struct hash<string_view>;
    template<> struct hash<u8string_view>;
    template<> struct hash<u16string_view>;
    template<> struct hash<u32string_view>;
    template<> struct hash<wstring_view>;

    inline namespace literals {
    inline namespace string_view_literals {
    // suffix for basic_string_view literals
    constexpr string_view operator "" sv(const char* str, size_t len) noexcept;
    constexpr u8string_view operator "" sv(const char16_t* str, size_t len) noexcept;
    constexpr u16string_view operator "" sv(const char16_t* str, size_t len) noexcept;
    constexpr u32string_view operator "" sv(const char32_t* str, size_t len) noexcept;
    constexpr wstring_view operator "" sv(const wchar_t* str, size_t len) noexcept;
    }
    }
    } // namespace std

#### Class template std::basic_string_view

    namespace std {
    template<class charT, class traits = char_traits<charT>>
    class basic_string_view {
    public:
    // types
    typedef traits traits_type;
    typedef charT value_type;
    typedef charT* pointer;
    typedef const charT* const_pointer;
    typedef charT& reference;
    typedef const charT& const_reference;
    typedef /*implementation-defined*/ const_iterator;
    typedef const_iterator iterator;
    typedef reverse_iterator<const_iterator> const_reverse_iterator;
    typedef const_reverse_iterator reverse_iterator;
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    static constexpr size_type npos = size_type(-1);

    // construction and assignment
    constexpr basic_string_view() noexcept;
    constexpr basic_string_view(const basic_string_view&) noexcept = default;
    basic_string_view &operator=(const basic_string_view&) noexcept = default;
    constexpr basic_string_view(const charT* str);
    constexpr basic_string_view(const charT* str, size_type len);

    // iterator support
    constexpr const_iterator begin() const noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr const_iterator cbegin() const noexcept;
    constexpr const_iterator cend() const noexcept;
    constexpr const_reverse_iterator rbegin() const noexcept;
    constexpr const_reverse_iterator rend() const noexcept;
    constexpr const_reverse_iterator crbegin() const noexcept;
    constexpr const_reverse_iterator crend() const noexcept;

    // capacity
    constexpr size_type size() const noexcept;
    constexpr size_type length() const noexcept;
    constexpr size_type max_size() const noexcept;
    [[nodiscard]] constexpr bool empty() const noexcept;

    // element access
    constexpr const_reference operator[](size_type pos) const;
    constexpr const_reference at(size_type pos) const;
    constexpr const_reference front() const;
    constexpr const_reference back() const;
    constexpr const_pointer data() const noexcept;

    // modifiers
    constexpr void remove_prefix(size_type n);
    constexpr void remove_suffix(size_type n);
    constexpr void swap(basic_string_view& s) noexcept;

    constexpr size_type copy(charT* s, size_type n, size_type pos = 0) const;
    constexpr basic_string_view substr(size_type pos = 0, size_type n = npos) const;
    constexpr int compare(basic_string_view s) const noexcept;
    constexpr int compare(size_type pos1, size_type n1, basic_string_view s) const;
    constexpr int compare(size_type pos1, size_type n1, basic_string_view s,
                          size_type pos2, size_type n2) const;
    constexpr int compare(const charT* s) const;
    constexpr int compare(size_type pos1, size_type n1, const charT* s) const;
    constexpr int compare(size_type pos1, size_type n1, const charT* s, size_type n2) const;
    constexpr bool starts_with(basic_string_view x) const noexcept;
    constexpr bool starts_with(charT x) const noexcept;
    constexpr bool starts_with(const charT* x) const;
    constexpr bool ends_with(basic_string_view x) const noexcept;
    constexpr bool ends_with(charT x) const noexcept;
    constexpr bool ends_with(const charT* x) const;
    constexpr size_type find(basic_string_view s, size_type pos = 0) const noexcept;
    constexpr size_type find(charT c, size_type pos = 0) const noexcept;
    constexpr size_type find(const charT* s, size_type pos, size_type n) const;
    constexpr size_type find(const charT* s, size_type pos = 0) const;
    constexpr size_type rfind(basic_string_view s, size_type pos = npos) const noexcept;
    constexpr size_type rfind(charT c, size_type pos = npos) const noexcept;
    constexpr size_type rfind(const charT* s, size_type pos, size_type n) const;
    constexpr size_type rfind(const charT* s, size_type pos = npos) const;
    constexpr size_type find_first_of(basic_string_view s, size_type pos = 0) const noexcept;
    constexpr size_type find_first_of(charT c, size_type pos = 0) const noexcept;
    constexpr size_type find_first_of(const charT* s, size_type pos, size_type n) const;
    constexpr size_type find_first_of(const charT* s, size_type pos = 0) const;
    constexpr size_type find_last_of(basic_string_view s, size_type pos = npos) const noexcept;
    constexpr size_type find_last_of(charT c, size_type pos = npos) const noexcept;
    constexpr size_type find_last_of(const charT* s, size_type pos, size_type n) const;
    constexpr size_type find_last_of(const charT* s, size_type pos = npos) const;
    constexpr size_type find_first_not_of(basic_string_view s, size_type pos = 0) const noexcept;
    constexpr size_type find_first_not_of(charT c, size_type pos = 0) const noexcept;
    constexpr size_type find_first_not_of(const charT* s, size_type pos, size_type n) const;
    constexpr size_type find_first_not_of(const charT* s, size_type pos = 0) const;
    constexpr size_type find_last_not_of(basic_string_view s,size_type pos = npos) const noexcept;
    constexpr size_type find_last_not_of(charT c, size_type pos = npos) const noexcept;
    constexpr size_type find_last_not_of(const charT* s, size_type pos, size_type n) const;
    constexpr size_type find_last_not_of(const charT* s, size_type pos = npos) const;
    private:
    const_pointer data_; // exposition only
    size_type size_; // exposition only
    };

    }

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