Standard library header <string>

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Standard Library header files

Language Support
<cstddef> <limits> <climits>	<cfloat> <cstdint> <new>	<typeinfo> <exception> <initializer_list>	<csignal> <csetjmp> <cstdarg>
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error>
General utilities
<utility> <memory> <memory_resource> <scoped_allocator>	<tuple> <optional> <any> <variant>	<bitset> <functional> <type_traits> <ratio>	<chrono> <ctime> <typeindex> <cstdlib>
Strings
<string> <string_view>	<cctype> <cwctype>	<cwchar> <cuchar>	<cstring>
Localization
<locale>	<codecvt>	<clocale>
Containers
<array> <deque> <vector>	<forward_list> <list>	<map> <set> <queue>	<unordered_map> <unordered_set> <stack>
Iterators
<iterator>
Algorithms
<algorithm>	<execution_policy>
Numerics
<complex> <random>	<valarray> <numeric>	<cfenv> <cmath>
Input/Output
<iosfwd> <iostream> <ios>	<streambuf> <istream> <ostream>	<iomanip> <sstream> <fstream>	<filesystem> <cstdio> <cinttypes>
Regular expressions
<regex>
Thread support
<thread> <atomic>	<mutex> <shared_mutex>	<condition_variable> <future>
C compatibility
<ciso646> <cstdalign>	<cstdbool> <ccomplex>	<ctgmath>

 

This header is part of the strings library.

Includes

<initializer_list>

(since C++11)

Classes

Name	Description
std::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<char16_t> (C++11)	(class template specialization)
std::char_traits<char32_t> (C++11)	(class template specialization)
std::basic_string	Class template representing a text string object (class template)
std::string	std::basic_string<char> (typedef)
std::wstring	std::basic_string<wchar_t> (typedef)
std::u16string (C++11)	std::basic_string<char16_t> (typedef)
std::u32string (C++11)	std::basic_string<char32_t> (typedef)
std::hash<std::string> (C++11)	(class template specialization)
std::hash<std::u16string> (C++11)	(class template specialization)
std::hash<std::u32string> (C++11)	(class template specialization)
std::hash<std::wstring> (C++11)	(class template specialization)

Functions

operator+	concatenates two strings or a string and a char (function template)
operator==operator!=operator<operator>operator<=operator>=	lexicographically compares two strings (function template)
std::swap(std::basic_string)	specializes the std::swap algorithm (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)

Literals

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

Synopsis

#include <initializer_list>
namespace std {
  // character traits
  template<class charT> struct char_traits;
  template<> struct char_traits<char>;
  template<> struct char_traits<char16_t>;
  template<> struct char_traits<char32_t>;
  template<> struct char_traits<wchar_t>;
  // basic_string
  template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>
  class basic_string;
  template<class charT, class traits, class Allocator>
  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>
  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>
  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>
  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>
  basic_string<charT, traits, Allocator> operator+(const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(const charT* lhs, basic_string<charT, traits, Allocator>&& rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(charT lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(charT lhs, basic_string<charT, traits, Allocator>&& rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(basic_string<charT, traits, Allocator>&& lhs,
const charT* rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(const basic_string<charT, traits, Allocator>& lhs, charT rhs);
  template<class charT, class traits, class Allocator>
  basic_string<charT, traits, Allocator> operator+(basic_string<charT, traits, Allocator>&& lhs, charT rhs);
  template<class charT, class traits, class Allocator>
  bool operator==(const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator==(const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  bool operator==(const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  bool operator!=(const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator!=(const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  bool operator!=(const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  bool operator< (const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator< (const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  bool operator< (const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  bool operator> (const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator> (const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
template<class charT, class traits, class Allocator>
  bool operator> (const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  bool operator<=(const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator<=(const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  bool operator<=(const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  template<class charT, class traits, class Allocator>
  bool operator>=(const basic_string<charT, traits, Allocator>& lhs, const basic_string<charT, traits, Allocator>& rhs) noexcept;
  template<class charT, class traits, class Allocator>
  bool operator>=(const basic_string<charT, traits, Allocator>& lhs, const charT* rhs);
  template<class charT, class traits, class Allocator>
  bool operator>=(const charT* lhs, const basic_string<charT, traits, Allocator>& rhs);
  // swap
  template<class charT, class traits, class Allocator>
  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);
  // basic_string typedef names
  using string = basic_string<char>;
  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 = 0, int base = 10);
  long stol(const string& str, size_t* idx = 0, int base = 10);
  unsigned long stoul(const string& str, size_t* idx = 0, int base = 10);
  long long stoll(const string& str, size_t* idx = 0, int base = 10);
  unsigned long long stoull(const string& str, size_t* idx = 0, int base = 10);
  float stof(const string& str, size_t* idx = 0);
  double stod(const string& str, size_t* idx = 0);
  long double stold(const string& str, size_t* idx = 0);
  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 = 0, int base = 10);
  long stol(const wstring& str, size_t* idx = 0, int base = 10);
  unsigned long stoul(const wstring& str, size_t* idx = 0, int base = 10);
  long long stoll(const wstring& str, size_t* idx = 0, int base = 10);
  unsigned long long stoull(const wstring& str, size_t* idx = 0, int base = 10);
  float stof(const wstring& str, size_t* idx = 0);
  double stod(const wstring& str, size_t* idx = 0);
  long double stold(const wstring& str, size_t* idx = 0);
  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);
  // hash support
  template<class T> struct hash;
  template<> struct hash<string>;
  template<> struct hash<u16string>;
  template<> struct hash<u32string>;
  template<> struct hash<wstring>;
  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 u16string = basic_string<char16_t>;
    using u32string = basic_string<char32_t>;
    using wstring = basic_string<wchar_t>;
  }
  inline namespace literals {
    inline namespace string_literals {
      // suffix for basic_string literals
      string operator""s(const char* str, size_t len);
      u16string operator""s(const char16_t* str, size_t len);
      u32string operator""s(const char32_t* str, size_t len);
      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;
    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 char_type* move(char_type* s1, const char_type* s2, size_t n);
    static char_type* copy(char_type* s1, const char_type* s2, size_t n);
    static 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;
    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 char_type* move(char_type* s1, const char_type* s2, size_t n);
    static char_type* copy(char_type* s1, const char_type* s2, size_t n);
    static 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;
    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 char_type* move(char_type* s1, const char_type* s2, size_t n);
    static char_type* copy(char_type* s1, const char_type* s2, size_t n);
    static 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;
    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 char_type* move(char_type* s1, const char_type* s2, size_t n);
    static char_type* copy(char_type* s1, const char_type* s2, size_t n);
    static 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 = /* see definition */ ;
    using const_iterator = /* see definition */ ;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    static const size_type npos = -1;
    // construct/copy/destroy
    basic_string() noexcept(noexcept(Allocator())) : basic_string(Allocator()) { }
    explicit basic_string(const Allocator& a) noexcept;
    basic_string(const basic_string& str);
    basic_string(basic_string&& str) noexcept;
    basic_string(const basic_string& str, size_type pos, const Allocator& a = Allocator());
    basic_string(const basic_string& str, size_type pos, size_type n, const Allocator& a = Allocator());
    template<class T>
    basic_string(const T& t, size_type pos, size_type n, const Allocator& a = Allocator());
    explicit basic_string(basic_string_view<charT, traits> sv, const Allocator& a = Allocator());
    basic_string(const charT* s, size_type n, const Allocator& a = Allocator());
    basic_string(const charT* s, const Allocator& a = Allocator());
    basic_string(size_type n, charT c, const Allocator& a = Allocator());
    template<class InputIterator>
    basic_string(InputIterator begin, InputIterator end, const Allocator& a = Allocator());
    basic_string(initializer_list<charT>, const Allocator& = Allocator());
    basic_string(const basic_string&, const Allocator&);
    basic_string(basic_string&&, const Allocator&);
    ~basic_string();
    basic_string& operator=(const basic_string& str);
    basic_string& operator=(basic_string&& str) noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
allocator_traits<Allocator>::is_always_equal::value);
    basic_string& operator=(basic_string_view<charT, traits> sv);
    basic_string& operator=(const charT* s);
    basic_string& operator=(charT c);
    basic_string& operator=(initializer_list<charT>);
    // iterators
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;
    reverse_iterator rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    reverse_iterator rend() noexcept;
    const_reverse_iterator rend() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    const_reverse_iterator crend() const noexcept;
    // capacity
    size_type size() const noexcept;
    size_type length() const noexcept;
    size_type max_size() const noexcept;
    void resize(size_type n, charT c);
    void resize(size_type n);
    size_type capacity() const noexcept;
    void reserve(size_type res_arg = 0);
    void shrink_to_fit();
    void clear() noexcept;
    bool empty() const noexcept;
    // element access
    const_reference operator[](size_type pos) const;
    reference operator[](size_type pos);
    const_reference at(size_type n) const;
    reference at(size_type n);
    const charT& front() const;
    charT& front();
    const charT& back() const;
    charT& back();
    // modifiers
    basic_string& operator+=(const basic_string& str);
    basic_string& operator+=(basic_string_view<charT, traits> sv);
    basic_string& operator+=(const charT* s);
    basic_string& operator+=(charT c);
    basic_string& operator+=(initializer_list<charT>);
    basic_string& append(const basic_string& str);
    basic_string& append(const basic_string& str, size_type pos, size_type n = npos);
    basic_string& append(basic_string_view<charT, traits> sv);
    template<class T>
    basic_string& append(const T& t, size_type pos, size_type n = npos);
    basic_string& append(const charT* s, size_type n);
    basic_string& append(const charT* s);
    basic_string& append(size_type n, charT c);
    template<class InputIterator>
    basic_string& append(InputIterator first, InputIterator last);
    basic_string& append(initializer_list<charT>);
    void push_back(charT c);
    basic_string& assign(const basic_string& str);
    basic_string& assign(basic_string&& str) noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
allocator_traits<Allocator>::is_always_equal::value);
    basic_string& assign(const basic_string& str, size_type pos, size_type n = npos);
    basic_string& assign(basic_string_view<charT, traits> sv);
    template<class T>
    basic_string& assign(const T& t, size_type pos, size_type n = npos);
    basic_string& assign(const charT* s, size_type n);
    basic_string& assign(const charT* s);
    basic_string& assign(size_type n, charT c);
    template<class InputIterator>
    basic_string& assign(InputIterator first, InputIterator last);
    basic_string& assign(initializer_list<charT>);
    basic_string& insert(size_type pos, const basic_string& str);
    basic_string& insert(size_type pos1, const basic_string& str, size_type pos2, size_type n = npos);
    basic_string& insert(size_type pos, basic_string_view<charT, traits> sv);
    template<class T>
    basic_string& insert(size_type pos1, const T& t, size_type pos2, size_type n = npos);
    basic_string& insert(size_type pos, const charT* s, size_type n);
    basic_string& insert(size_type pos, const charT* s);
    basic_string& insert(size_type pos, size_type n, charT c);
    iterator insert(const_iterator p, charT c);
    iterator insert(const_iterator p, size_type n, charT c);
    template<class InputIterator>
    iterator insert(const_iterator p, InputIterator first, InputIterator last);
    iterator insert(const_iterator p, initializer_list<charT>);
    basic_string& erase(size_type pos = 0, size_type n = npos);
    iterator erase(const_iterator p);
    iterator erase(const_iterator first, const_iterator last);
    void pop_back();
    basic_string& replace(size_type pos1, size_type n1, const basic_string& str);
    basic_string& replace(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos);
    basic_string& replace(size_type pos1, size_type n1, basic_string_view<charT, traits> sv);
    template<class T>
    basic_string& replace(size_type pos1, size_type n1, const T& t, size_type pos2, size_type n2 = npos);
    basic_string& replace(size_type pos, size_type n1, const charT* s, size_type n2);
    basic_string& replace(size_type pos, size_type n1, const charT* s);
    basic_string& replace(size_type pos, size_type n1, size_type n2, charT c);
    basic_string& replace(const_iterator i1, const_iterator i2, const basic_string& str);
    basic_string& replace(const_iterator i1, const_iterator i2, basic_string_view<charT, traits> sv);
    basic_string& replace(const_iterator i1, const_iterator i2, const charT* s, size_type n);
    basic_string& replace(const_iterator i1, const_iterator i2, const charT* s);
    basic_string& replace(const_iterator i1, const_iterator i2, size_type n, charT c);
    template<class InputIterator>
    basic_string& replace(const_iterator i1, const_iterator i2, InputIterator j1, InputIterator j2);
    basic_string& replace(const_iterator, const_iterator, initializer_list<charT>);
    size_type copy(charT* s, size_type n, size_type pos = 0) const;
    void swap(basic_string& str) noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
allocator_traits<Allocator>::is_always_equal::value);
    // string operations
    const charT* c_str() const noexcept;
    const charT* data() const noexcept;
    charT* data() noexcept;
    operator basic_string_view<charT, traits>() const noexcept;
    allocator_type get_allocator() const noexcept;
    size_type find (basic_string_view<charT, traits> sv, size_type pos = 0) const noexcept;
    size_type find (const basic_string& str, size_type pos = 0) const noexcept;
    size_type find (const charT* s, size_type pos, size_type n) const;
    size_type find (const charT* s, size_type pos = 0) const;
    size_type find (charT c, size_type pos = 0) const;
    size_type rfind(basic_string_view<charT, traits> sv, size_type pos = npos) const noexcept;
    size_type rfind(const basic_string& str, size_type pos = npos) const noexcept;
    size_type rfind(const charT* s, size_type pos, size_type n) const;
    size_type rfind(const charT* s, size_type pos = npos) const;
    size_type rfind(charT c, size_type pos = npos) const;
    size_type find_first_of(basic_string_view<charT, traits> sv, size_type pos = 0) const noexcept;
    size_type find_first_of(const basic_string& str, size_type pos = 0) const noexcept;
    size_type find_first_of(const charT* s, size_type pos, size_type n) const;
    size_type find_first_of(const charT* s, size_type pos = 0) const;
    size_type find_first_of(charT c, size_type pos = 0) const;
    size_type find_last_of (basic_string_view<charT, traits> sv, size_type pos = npos) const noexcept;
    size_type find_last_of (const basic_string& str, size_type pos = npos) const noexcept;
    size_type find_last_of (const charT* s, size_type pos, size_type n) const;
    size_type find_last_of (const charT* s, size_type pos = npos) const;
    size_type find_last_of (charT c, size_type pos = npos) const;
    size_type find_first_not_of(basic_string_view<charT, traits> sv, size_type pos = 0) const noexcept;
    size_type find_first_not_of(const basic_string& str, size_type pos = 0) const noexcept;
    size_type find_first_not_of(const charT* s, size_type pos, size_type n) const;
    size_type find_first_not_of(const charT* s, size_type pos = 0) const;
    size_type find_first_not_of(charT c, size_type pos = 0) const;
    size_type find_last_not_of (basic_string_view<charT, traits> sv, size_type pos = npos) const noexcept;
    size_type find_last_not_of (const basic_string& str, size_type pos = npos) const noexcept;
    size_type find_last_not_of (const charT* s, size_type pos, size_type n) const;
    size_type find_last_not_of (const charT* s, size_type pos = npos) const;
    size_type find_last_not_of (charT c, size_type pos = npos) const;
    basic_string substr(size_type pos = 0, size_type n = npos) const;
    int compare(basic_string_view<charT, traits> sv) const noexcept;
    int compare(size_type pos1, size_type n1,
    basic_string_view<charT, traits> sv) const;
    template<class T>
    int compare(size_type pos1, size_type n1, const T& t, size_type pos2, size_type n2 = npos) const;
    int compare(const basic_string& str) const noexcept;
    int compare(size_type pos1, size_type n1, const basic_string& str) const;
    int compare(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos) const;
    int compare(const charT* s) const;
    int compare(size_type pos1, size_type n1, const charT* s) const;
    int compare(size_type pos1, size_type n1, const charT* s, size_type n2) const;
  };
  template<class InputIterator,
  class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
  basic_string(InputIterator, InputIterator, Allocator = Allocator())
  -> basic_string<typename iterator_traits<InputIterator>::value_type,
                  char_traits<typename iterator_traits<InputIterator>::value_type>,
                  Allocator>;
}