# Standard library header <string>

From cppreference.com
< cpp‎ | header

This header is part of the strings library.

### Includes

<compare> (C++20) | Three-way comparison operator support
<initializer_list> (C++11) | std::initializer_list class template

### Classes

char_traits | Class Template which describes properties of a character type (class template)
std::char_traits <char> | (class template specialization)
std::char_traits <wchar_t> | (class template specialization)
std::char_traits <char8_t> (C++20) | (class template specialization)
std::char_traits <char16_t> (C++11) | (class template specialization)
std::char_traits <char32_t> (C++11) | (class template specialization)
basic_string | stores and manipulates sequences of characters (class template)
std::string | std::basic_string <char> (typedef)
std::u8string (C++20) | std::basic_string <char8_t> (typedef)
std::u16string (C++11) | std::basic_string <char16_t> (typedef)
std::u32string (C++11) | std::basic_string <char32_t> (typedef)
std::wstring | std::basic_string <wchar_t> (typedef)
std::pmr::basic_string (C++17) | (alias template)
std::pmr::string (C++17) | std::pmr::basic_string <char> (typedef)
std::pmr::u8string (C++20) | std::pmr::basic_string <char8_t> (typedef)
std::pmr::u16string (C++17) | std::pmr::basic_string <char16_t> (typedef)
std::pmr::u32string (C++17) | std::pmr::basic_string <char32_t> (typedef)
std::pmr::wstring (C++17) | std::pmr::basic_string <wchar_t> (typedef)
std::hash<std::basic_string> (C++11) | hash support for strings (class template specialization)

### Functions

operator+ | concatenates two strings, a string and a char, or a string and string_view (function template)
operator==operator!=operator<operator>operator<=operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20) | lexicographically compares two strings (function template)
std::swap(std::basic_string) | specializes the std::swap algorithm (function template)
erase(std::basic_string)erase_if(std::basic_string) (C++20) | erases all elements satisfying specific criteria (function template)

##### Input/output

operator<<operator>> | performs stream input and output on strings (function template)
getline | read data from an I/O stream into a string (function template)

##### Numeric conversions

stoistolstoll (C++11)(C++11)(C++11) | converts a string to a signed integer (function)
stoulstoull (C++11)(C++11) | converts a string to an unsigned integer (function)
stofstodstold (C++11)(C++11)(C++11) | converts a string to a floating point value (function)
to_string (C++11) | converts an integral or floating-point value to `string` (function)
to_wstring (C++11) | converts an integral or floating-point value to `wstring` (function)

##### Range access

begincbegin (C++11)(C++14) | returns an iterator to the beginning of a container or array (function template)
endcend (C++11)(C++14) | returns an iterator to the end of a container or array (function template)
rbegincrbegin (C++14) | returns a reverse iterator to the beginning of a container or array (function template)
rendcrend (C++14) | returns a reverse end iterator for a container or array (function template)
sizessize (C++17)(C++20) | returns the size of a container or array (function template)
empty (C++17) | checks whether the container is empty (function template)
data (C++17) | obtains the pointer to the underlying array (function template)

##### Literals

Defined in inline namespace `std::literals::string_literals`
operator""s (C++14) | converts a character array literal to `basic_string` (function)

### Synopsis

    #include <compare>
    #include <initializer_list>

    namespace std {
      // character traits
      template<class CharT> struct char_traits; // freestanding
      template<> struct char_traits<char>;      // freestanding
      template<> struct char_traits<char8_t>;   // freestanding
      template<> struct char_traits<char16_t>;  // freestanding
      template<> struct char_traits<char32_t>;  // freestanding
      template<> struct char_traits<wchar_t>;   // freestanding

      // basic_string
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_string;

      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const basic_string<CharT, Traits, Allocator>& lhs,
                    const basic_string<CharT, Traits, Allocator>& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(basic_string<CharT, Traits, Allocator>&& lhs,
                    const basic_string<CharT, Traits, Allocator>& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const basic_string<CharT, Traits, Allocator>& lhs,
                    basic_string<CharT, Traits, Allocator>&& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(basic_string<CharT, Traits, Allocator>&& lhs,
                    basic_string<CharT, Traits, Allocator>&& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const CharT* lhs,
                    const basic_string<CharT, Traits, Allocator>& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const CharT* lhs,
                    basic_string<CharT, Traits, Allocator>&& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(CharT lhs,
                    const basic_string<CharT, Traits, Allocator>& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(CharT lhs,
                    basic_string<CharT, Traits, Allocator>&& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const basic_string<CharT, Traits, Allocator>& lhs,
                    const CharT* rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(basic_string<CharT, Traits, Allocator>&& lhs,
                    const CharT* rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const basic_string<CharT, Traits, Allocator>& lhs,
                    CharT rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(basic_string<CharT, Traits, Allocator>&& lhs,
                    CharT rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(const basic_string<CharT, Traits, Allocator>& lhs,
                    type_identity_t<basic_string_view<CharT, Traits>> rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(basic_string<CharT, Traits, Allocator>&& lhs,
                    type_identity_t<basic_string_view<CharT, Traits>> rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(type_identity_t<basic_string_view<CharT, Traits>> lhs,
                    const basic_string<CharT, Traits, Allocator>& rhs);
      template<class CharT, class Traits, class Allocator>
        constexpr basic_string<CharT, Traits, Allocator>
          operator+(type_identity_t<basic_string_view<CharT, Traits>> lhs,
                    basic_string<CharT, Traits, Allocator>&& rhs);

      template<class CharT, class Traits, class Allocator>
        constexpr bool
          operator==(const basic_string<CharT, Traits, Allocator>& lhs,
                     const basic_string<CharT, Traits, Allocator>& rhs) noexcept;
      template<class CharT, class Traits, class Allocator>
        constexpr bool operator==(const basic_string<CharT, Traits, Allocator>& lhs,
                                  const CharT* rhs);

      template<class CharT, class Traits, class Allocator>
        constexpr /* see description */ operator<=>(const basic_string<CharT,
                                                    Traits, Allocator>& lhs,
                                                    const basic_string<CharT,
                                                    Traits, Allocator>& rhs) noexcept;
      template<class CharT, class Traits, class Allocator>
        constexpr /* see description */ operator<=>(const basic_string<CharT,
                                                    Traits, Allocator>& lhs,
                                                    const CharT* rhs);

      // swap
      template<class CharT, class Traits, class Allocator>
        constexpr void
          swap(basic_string<CharT, Traits, Allocator>& lhs,
               basic_string<CharT, Traits, Allocator>& rhs)
            noexcept(noexcept(lhs.swap(rhs)));

      // inserters and extractors
      template<class CharT, class Traits, class Allocator>
        basic_istream<CharT, Traits>&
          operator>>(basic_istream<CharT, Traits>& is,
                     basic_string<CharT, Traits, Allocator>& str);
      template<class CharT, class Traits, class Allocator>
        basic_ostream<CharT, Traits>&
          operator<<(basic_ostream<CharT, Traits>& os,
                     const basic_string<CharT, Traits, Allocator>& str);
      template<class CharT, class Traits, class Allocator>
        basic_istream<CharT, Traits>&
          getline(basic_istream<CharT, Traits>& is,
                  basic_string<CharT, Traits, Allocator>& str,
                  CharT delim);
      template<class CharT, class Traits, class Allocator>
        basic_istream<CharT, Traits>&
          getline(basic_istream<CharT, Traits>&& is,
                  basic_string<CharT, Traits, Allocator>& str,
                  CharT delim);
      template<class CharT, class Traits, class Allocator>
        basic_istream<CharT, Traits>&
          getline(basic_istream<CharT, Traits>& is,
                  basic_string<CharT, Traits, Allocator>& str);
      template<class CharT, class Traits, class Allocator>
        basic_istream<CharT, Traits>&
          getline(basic_istream<CharT, Traits>&& is,
                  basic_string<CharT, Traits, Allocator>& str);

      // erasure
      template<class CharT, class Traits, class Allocator, class U = CharT>
        constexpr typename basic_string<CharT, Traits, Allocator>::size_type
          erase(basic_string<CharT, Traits, Allocator>& c, const U& value);
      template<class CharT, class Traits, class Allocator, class Pred>
        constexpr typename basic_string<CharT, Traits, Allocator>::size_type
          erase_if(basic_string<CharT, Traits, Allocator>& c, Pred pred);

      // basic_string typedef-names
      using string    = basic_string<char>;
      using u8string  = basic_string<char8_t>;
      using u16string = basic_string<char16_t>;
      using u32string = basic_string<char32_t>;
      using wstring   = basic_string<wchar_t>;

      // numeric conversions
      int stoi(const string& str, size_t* idx = nullptr, int base = 10);
      long stol(const string& str, size_t* idx = nullptr, int base = 10);
      unsigned long stoul(const string& str, size_t* idx = nullptr, int base = 10);
      long long stoll(const string& str, size_t* idx = nullptr, int base = 10);
      unsigned long long stoull(const string& str, size_t* idx = nullptr, int base = 10);
      float stof(const string& str, size_t* idx = nullptr);
      double stod(const string& str, size_t* idx = nullptr);
      long double stold(const string& str, size_t* idx = nullptr);
      string to_string(int val);
      string to_string(unsigned val);
      string to_string(long val);
      string to_string(unsigned long val);
      string to_string(long long val);
      string to_string(unsigned long long val);
      string to_string(float val);
      string to_string(double val);
      string to_string(long double val);

      int stoi(const wstring& str, size_t* idx = nullptr, int base = 10);
      long stol(const wstring& str, size_t* idx = nullptr, int base = 10);
      unsigned long stoul(const wstring& str, size_t* idx = nullptr, int base = 10);
      long long stoll(const wstring& str, size_t* idx = nullptr, int base = 10);
      unsigned long long stoull(const wstring& str, size_t* idx = nullptr, int base = 10);
      float stof(const wstring& str, size_t* idx = nullptr);
      double stod(const wstring& str, size_t* idx = nullptr);
      long double stold(const wstring& str, size_t* idx = nullptr);
      wstring to_wstring(int val);
      wstring to_wstring(unsigned val);
      wstring to_wstring(long val);
      wstring to_wstring(unsigned long val);
      wstring to_wstring(long long val);
      wstring to_wstring(unsigned long long val);
      wstring to_wstring(float val);
      wstring to_wstring(double val);
      wstring to_wstring(long double val);

      namespace pmr {
        template<class CharT, class Traits = char_traits<CharT>>
          using basic_string = std::basic_string<CharT, Traits, polymorphic_allocator<CharT>>;

        using string    = basic_string<char>;
        using u8string  = basic_string<char8_t>;
        using u16string = basic_string<char16_t>;
        using u32string = basic_string<char32_t>;
        using wstring   = basic_string<wchar_t>;
      }

      // hash support
      template<class T> struct hash;
      template<class A> struct hash<basic_string<char, char_traits<char>, A>>;
      template<class A> struct hash<basic_string<char8_t, char_traits<char8_t>, A>>;
      template<class A> struct hash<basic_string<char16_t, char_traits<char16_t>, A>>;
      template<class A> struct hash<basic_string<char32_t, char_traits<char32_t>, A>>;
      template<class A> struct hash<basic_string<wchar_t, char_traits<wchar_t>, A>>;

      inline namespace literals {
      inline namespace string_literals {
        // suffix for basic_string literals
        constexpr string    operator""s(const char* str, size_t len);
        constexpr u8string  operator""s(const char8_t* str, size_t len);
        constexpr u16string operator""s(const char16_t* str, size_t len);
        constexpr u32string operator""s(const char32_t* str, size_t len);
        constexpr wstring   operator""s(const wchar_t* str, size_t len);
      }
      }
    }

#### Class template std::char_traits

    namespace std {
      template<> struct char_traits<char> {
        using char_type  = char;
        using int_type   = int;
        using off_type   = streamoff;
        using pos_type   = streampos;
        using state_type = mbstate_t;
        using comparison_category = strong_ordering;

        static constexpr void assign(char_type& c1, const char_type& c2) noexcept;
        static constexpr bool eq(char_type c1, char_type c2) noexcept;
        static constexpr bool lt(char_type c1, char_type c2) noexcept;

        static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
        static constexpr size_t length(const char_type* s);
        static constexpr const char_type* find(const char_type* s, size_t n,
                                               const char_type& a);
        static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* assign(char_type* s, size_t n, char_type a);

        static constexpr int_type not_eof(int_type c) noexcept;
        static constexpr char_type to_char_type(int_type c) noexcept;
        static constexpr int_type to_int_type(char_type c) noexcept;
        static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept;
        static constexpr int_type eof() noexcept;
      };

      template<> struct char_traits<char8_t> {
        using char_type  = char8_t;
        using int_type   = unsigned int;
        using off_type   = streamoff;
        using pos_type   = u8streampos;
        using state_type = mbstate_t;
        using comparison_category = strong_ordering;

        static constexpr void assign(char_type& c1, const char_type& c2) noexcept;
        static constexpr bool eq(char_type c1, char_type c2) noexcept;
        static constexpr bool lt(char_type c1, char_type c2) noexcept;

        static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
        static constexpr size_t length(const char_type* s);
        static constexpr const char_type* find(const char_type* s, size_t n,
                                               const char_type& a);
        static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* assign(char_type* s, size_t n, char_type a);
        static constexpr int_type not_eof(int_type c) noexcept;
        static constexpr char_type to_char_type(int_type c) noexcept;
        static constexpr int_type to_int_type(char_type c) noexcept;
        static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept;
        static constexpr int_type eof() noexcept;
      };

      template<> struct char_traits<char16_t> {
        using char_type  = char16_t;
        using int_type   = uint_least16_t;
        using off_type   = streamoff;
        using pos_type   = u16streampos;
        using state_type = mbstate_t;
        using comparison_category = strong_ordering;

        static constexpr void assign(char_type& c1, const char_type& c2) noexcept;
        static constexpr bool eq(char_type c1, char_type c2) noexcept;
        static constexpr bool lt(char_type c1, char_type c2) noexcept;

        static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
        static constexpr size_t length(const char_type* s);
        static constexpr const char_type* find(const char_type* s, size_t n,
                                               const char_type& a);
        static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* assign(char_type* s, size_t n, char_type a);

        static constexpr int_type not_eof(int_type c) noexcept;
        static constexpr char_type to_char_type(int_type c) noexcept;
        static constexpr int_type to_int_type(char_type c) noexcept;
        static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept;
        static constexpr int_type eof() noexcept;
      };

      template<> struct char_traits<char32_t> {
        using char_type  = char32_t;
        using int_type   = uint_least32_t;
        using off_type   = streamoff;
        using pos_type   = u32streampos;
        using state_type = mbstate_t;
        using comparison_category = strong_ordering;

        static constexpr void assign(char_type& c1, const char_type& c2) noexcept;
        static constexpr bool eq(char_type c1, char_type c2) noexcept;
        static constexpr bool lt(char_type c1, char_type c2) noexcept;

        static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
        static constexpr size_t length(const char_type* s);
        static constexpr const char_type* find(const char_type* s, size_t n,
                                               const char_type& a);
        static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* assign(char_type* s, size_t n, char_type a);

        static constexpr int_type not_eof(int_type c) noexcept;
        static constexpr char_type to_char_type(int_type c) noexcept;
        static constexpr int_type to_int_type(char_type c) noexcept;
        static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept;
        static constexpr int_type eof() noexcept;
      };

      template<> struct char_traits<wchar_t> {
        using char_type  = wchar_t;
        using int_type   = wint_t;
        using off_type   = streamoff;
        using pos_type   = wstreampos;
        using state_type = mbstate_t;
        using comparison_category = strong_ordering;

        static constexpr void assign(char_type& c1, const char_type& c2) noexcept;
        static constexpr bool eq(char_type c1, char_type c2) noexcept;
        static constexpr bool lt(char_type c1, char_type c2) noexcept;

        static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
        static constexpr size_t length(const char_type* s);
        static constexpr const char_type* find(const char_type* s, size_t n,
                                               const char_type& a);
        static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n);
        static constexpr char_type* assign(char_type* s, size_t n, char_type a);

        static constexpr int_type not_eof(int_type c) noexcept;
        static constexpr char_type to_char_type(int_type c) noexcept;
        static constexpr int_type to_int_type(char_type c) noexcept;
        static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept;
        static constexpr int_type eof() noexcept;
      };
    }

#### Class template std::basic_string

    namespace std {
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
      class basic_string {
      public:
        // types
        using traits_type            = Traits;
        using value_type             = CharT;
        using allocator_type         = Allocator;
        using size_type              = typename allocator_traits<Allocator>::size_type;
        using difference_type        = typename allocator_traits<Allocator>::difference_type;
        using pointer                = typename allocator_traits<Allocator>::pointer;
        using const_pointer          = typename allocator_traits<Allocator>::const_pointer;
        using reference              = value_type&;
        using const_reference        = const value_type&;

        using iterator               = /* implementation-defined */;
        using const_iterator         = /* implementation-defined */;
        using reverse_iterator       = std::reverse_iterator<iterator>;
        using const_reverse_iterator = std::reverse_iterator<const_iterator>;
        static constexpr size_type npos = size_type(-1);

        // construct/copy/destroy
        constexpr basic_string() noexcept(noexcept(Allocator()))
          : basic_string(Allocator()) { }
        constexpr explicit basic_string(const Allocator& a) noexcept;
        constexpr basic_string(const basic_string& str);
        constexpr basic_string(basic_string&& str) noexcept;
        constexpr basic_string(const basic_string& str, size_type pos,
                               const Allocator& a = Allocator());
        constexpr basic_string(const basic_string& str, size_type pos, size_type n,
                               const Allocator& a = Allocator());
        constexpr basic_string(basic_string&& str, size_type pos,
                               const Allocator& a = Allocator());
        constexpr basic_string(basic_string&& str, size_type pos, size_type n,
                               const Allocator& a = Allocator());
        template<class T>
          constexpr basic_string(const T& t, size_type pos, size_type n,
                                 const Allocator& a = Allocator());
        template<class T>
          constexpr explicit basic_string(const T& t, const Allocator& a = Allocator());
        constexpr basic_string(const CharT* s, size_type n, const Allocator& a = Allocator());
        constexpr basic_string(const CharT* s, const Allocator& a = Allocator());
        basic_string(nullptr_t) = delete;
        constexpr basic_string(size_type n, CharT c, const Allocator& a = Allocator());
        template<class InputIt>
          constexpr basic_string(InputIt begin, InputIt end,
                                 const Allocator& a = Allocator());
        template<container-compatible-range<CharT> R>
          constexpr basic_string(from_range_t, R&& rg, const Allocator& a = Allocator());
        constexpr basic_string(initializer_list<CharT>, const Allocator& = Allocator());
        constexpr basic_string(const basic_string&, const Allocator&);
        constexpr basic_string(basic_string&&, const Allocator&);
        constexpr ~basic_string();

        constexpr basic_string& operator=(const basic_string& str);
        constexpr basic_string& operator=(basic_string&& str)
          noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
                   allocator_traits<Allocator>::is_always_equal::value);
        template<class T>
          constexpr basic_string& operator=(const T& t);
        constexpr basic_string& operator=(const CharT* s);
        basic_string& operator=(nullptr_t) = delete;
        constexpr basic_string& operator=(CharT c);
        constexpr basic_string& operator=(initializer_list<CharT>);

        // iterators
        constexpr iterator       begin() noexcept;
        constexpr const_iterator begin() const noexcept;
        constexpr iterator       end() noexcept;
        constexpr const_iterator end() const noexcept;

        constexpr reverse_iterator       rbegin() noexcept;
        constexpr const_reverse_iterator rbegin() const noexcept;
        constexpr reverse_iterator       rend() noexcept;
        constexpr const_reverse_iterator rend() const noexcept;

        constexpr const_iterator         cbegin() const noexcept;
        constexpr const_iterator         cend() 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;
        constexpr void resize(size_type n, CharT c);
        constexpr void resize(size_type n);
        template<class Operation>
          constexpr void resize_and_overwrite(size_type n, Operation op);
        constexpr size_type capacity() const noexcept;
        constexpr void reserve(size_type res_arg);
        constexpr void shrink_to_fit();
        constexpr void clear() noexcept;
        constexpr bool empty() const noexcept;

        // element access
        constexpr const_reference operator[](size_type pos) const;
        constexpr reference       operator[](size_type pos);
        constexpr const_reference at(size_type n) const;
        constexpr reference       at(size_type n);

        constexpr const CharT& front() const;
        constexpr CharT&       front();
        constexpr const CharT& back() const;
        constexpr CharT&       back();

        // modifiers
        constexpr basic_string& operator+=(const basic_string& str);
        template<class T>
          constexpr basic_string& operator+=(const T& t);
        constexpr basic_string& operator+=(const CharT* s);
        constexpr basic_string& operator+=(CharT c);
        constexpr basic_string& operator+=(initializer_list<CharT>);
        constexpr basic_string& append(const basic_string& str);
        constexpr basic_string& append(const basic_string& str, size_type pos,
                                       size_type n = npos);
        template<class T>
          constexpr basic_string& append(const T& t);
        template<class T>
          constexpr basic_string& append(const T& t, size_type pos, size_type n = npos);
        constexpr basic_string& append(const CharT* s, size_type n);
        constexpr basic_string& append(const CharT* s);
        constexpr basic_string& append(size_type n, CharT c);
        template<class InputIt>
          constexpr basic_string& append(InputIt first, InputIt last);
        template<container-compatible-range<CharT> R>
          constexpr basic_string& append_range(R&& rg);
        constexpr basic_string& append(initializer_list<CharT>);

        constexpr void push_back(CharT c);

        constexpr basic_string& assign(const basic_string& str);
        constexpr basic_string& assign(basic_string&& str)
          noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
                   allocator_traits<Allocator>::is_always_equal::value);
        constexpr basic_string& assign(const basic_string& str, size_type pos,
                                       size_type n = npos);
        template<class T>
          constexpr basic_string& assign(const T& t);
        template<class T>
          constexpr basic_string& assign(const T& t, size_type pos, size_type n = npos);
        constexpr basic_string& assign(const CharT* s, size_type n);
        constexpr basic_string& assign(const CharT* s);
        constexpr basic_string& assign(size_type n, CharT c);
        template<class InputIt>
          constexpr basic_string& assign(InputIt first, InputIt last);
        template<container-compatible-range<CharT> R>
          constexpr basic_string& assign_range(R&& rg);
        constexpr basic_string& assign(initializer_list<CharT>);

        constexpr basic_string& insert(size_type pos, const basic_string& str);
        constexpr basic_string& insert(size_type pos1, const basic_string& str,
                                       size_type pos2, size_type n = npos);
        template<class T>
          constexpr basic_string& insert(size_type pos, const T& t);
        template<class T>
          constexpr basic_string& insert(size_type pos1, const T& t,
                                         size_type pos2, size_type n = npos);
        constexpr basic_string& insert(size_type pos, const CharT* s, size_type n);
        constexpr basic_string& insert(size_type pos, const CharT* s);
        constexpr basic_string& insert(size_type pos, size_type n, CharT c);
        constexpr iterator insert(const_iterator p, CharT c);
        constexpr iterator insert(const_iterator p, size_type n, CharT c);
        template<class InputIt>
          constexpr iterator insert(const_iterator p, InputIt first, InputIt last);
        template<container-compatible-range<CharT> R>
          constexpr iterator insert_range(const_iterator p, R&& rg);
        constexpr iterator insert(const_iterator p, initializer_list<CharT>);

        constexpr basic_string& erase(size_type pos = 0, size_type n = npos);
        constexpr iterator erase(const_iterator p);
        constexpr iterator erase(const_iterator first, const_iterator last);

        constexpr void pop_back();

        constexpr basic_string& replace(size_type pos1, size_type n1, const basic_string& str);
        constexpr basic_string& replace(size_type pos1, size_type n1, const basic_string& str,
                                        size_type pos2, size_type n2 = npos);
        template<class T>
          constexpr basic_string& replace(size_type pos1, size_type n1, const T& t);
        template<class T>
          constexpr basic_string& replace(size_type pos1, size_type n1, const T& t,
                                          size_type pos2, size_type n2 = npos);
        constexpr basic_string& replace(size_type pos, size_type n1, const CharT* s,
                                        size_type n2);
        constexpr basic_string& replace(size_type pos, size_type n1, const CharT* s);
        constexpr basic_string& replace(size_type pos, size_type n1, size_type n2, CharT c);
        constexpr basic_string& replace(const_iterator i1, const_iterator i2,
                                        const basic_string& str);
        template<class T>
          constexpr basic_string& replace(const_iterator i1, const_iterator i2, const T& t);
        constexpr basic_string& replace(const_iterator i1, const_iterator i2, const CharT* s,
                                        size_type n);
        constexpr basic_string& replace(const_iterator i1, const_iterator i2, const CharT* s);
        constexpr basic_string& replace(const_iterator i1, const_iterator i2, size_type n,
                                        CharT c);
        template<class InputIt>
          constexpr basic_string& replace(const_iterator i1, const_iterator i2,
                                          InputIt j1, InputIt j2);
        template<container-compatible-range<CharT> R>
          constexpr basic_string& replace_with_range(const_iterator i1, const_iterator i2,
                                                     R&& rg);
        constexpr basic_string& replace(const_iterator, const_iterator,
                                        initializer_list<CharT>);

        constexpr size_type copy(CharT* s, size_type n, size_type pos = 0) const;

        constexpr void swap(basic_string& str)
          noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
                   allocator_traits<Allocator>::is_always_equal::value);

        // string operations
        constexpr const CharT* c_str() const noexcept;
        constexpr const CharT* data() const noexcept;
        constexpr CharT* data() noexcept;
        constexpr operator basic_string_view<CharT, Traits>() const noexcept;
        constexpr allocator_type get_allocator() const noexcept;

        template<class T>
          constexpr size_type find(const T& t,
                                   size_type pos = 0) const noexcept(/* see description */);
        constexpr size_type find(const basic_string& str, 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 find(CharT c, size_type pos = 0) const noexcept;
        template<class T>
          constexpr size_type rfind(const T& t, size_type pos = npos)
            const noexcept(/* see description */);
        constexpr size_type rfind(const basic_string& str,
                                  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 rfind(CharT c, size_type pos = npos) const noexcept;

        template<class T>
          constexpr size_type find_first_of(const T& t, size_type pos = 0)
            const noexcept(/* see description */);
        constexpr size_type find_first_of(const basic_string& str,
                                          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_first_of(CharT c, size_type pos = 0) const noexcept;
        template<class T>
          constexpr size_type find_last_of(const T& t, size_type pos = npos)
            const noexcept(/* see description */);
        constexpr size_type find_last_of(const basic_string& str,
                                         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_last_of(CharT c, size_type pos = npos) const noexcept;

        template<class T>
          constexpr size_type find_first_not_of(const T& t, size_type pos = 0)
            const noexcept(/* see description */);
        constexpr size_type find_first_not_of(const basic_string& str,
                                              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_first_not_of(CharT c, size_type pos = 0) const noexcept;
        template<class T>
          constexpr size_type find_last_not_of(const T& t, size_type pos = npos)
            const noexcept(/* see description */);
        constexpr size_type find_last_not_of(const basic_string& str,
                                             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;
        constexpr size_type find_last_not_of(CharT c, size_type pos = npos) const noexcept;

        constexpr basic_string substr(size_type pos = 0, size_type n = npos) const &;
        constexpr basic_string substr(size_type pos = 0, size_type n = npos) &&;

        template<class T>
          constexpr int compare(const T& t) const noexcept(/* see description */);
        template<class T>
          constexpr int compare(size_type pos1, size_type n1, const T& t) const;
        template<class T>
          constexpr int compare(size_type pos1, size_type n1, const T& t,
                                size_type pos2, size_type n2 = npos) const;
        constexpr int compare(const basic_string& str) const noexcept;
        constexpr int compare(size_type pos1, size_type n1, const basic_string& str) const;
        constexpr int compare(size_type pos1, size_type n1, const basic_string& str,
                              size_type pos2, size_type n2 = npos) 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<CharT, Traits> 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<CharT, Traits> x) const noexcept;
        constexpr bool ends_with(CharT x) const noexcept;
        constexpr bool ends_with(const CharT* x) const;

        constexpr bool contains(basic_string_view<CharT, Traits> x) const noexcept;
        constexpr bool contains(CharT x) const noexcept;
        constexpr bool contains(const CharT* x) const;
      };

      template<class InputIt,
               class Allocator = allocator<typename iterator_traits<InputIt>::value_type>>
        basic_string(InputIt, InputIt, Allocator = Allocator())
          -> basic_string<typename iterator_traits<InputIt>::value_type,
                          char_traits<typename iterator_traits<InputIt>::value_type>,
                          Allocator>;

      template<ranges::input_range R,
               class Allocator = allocator<ranges::range_value_t<R>>>
        basic_string(from_range_t, R&&, Allocator = Allocator())
          -> basic_string<ranges::range_value_t<R>, char_traits<ranges::range_value_t<R>>,
                          Allocator>;

      template<class CharT,
               class Traits,
               class Allocator = allocator<CharT>>
        explicit basic_string(basic_string_view<CharT, Traits>, const Allocator& = Allocator())
          -> basic_string<CharT, Traits, Allocator>;

      template<class CharT,
               class Traits,
               class Allocator = allocator<CharT>>
        basic_string(basic_string_view<CharT, Traits>,
                     typename /* see description */::size_type,
                     typename /* see description */::size_type,
                     const Allocator& = Allocator())
          -> basic_string<CharT, Traits, Allocator>;
    }

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---

LWG 209

C++98

the declarations of the following std::basic_string
members used inconsistent styles in the synopsis:

- `void push_back(CharT c);`
- `basic_string& assign(const basic_string& str);`
- `void swap(basic_string& str);`

uniformed the styles

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