Standard library header <string>

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Standard Library headers

Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.

Language Support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11)   <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error> (C++11)
General utilities
<utility> <memory> <memory_resource> (C++17) <scoped_allocator> (C++11)   <expected> (C++23)	<bitset> <tuple> (C++11) <optional> (C++17) <any> (C++17)	<variant> (C++17) <type_traits> (C++11) <ratio> (C++11) <chrono> (C++11)	<typeindex> (C++11) <functional> <stacktrace> (C++23) <ctime>
Strings
<string> <string_view> (C++17) <cstring>	<charconv> (C++17) <format> (C++20)	<cctype> <cwctype>	<cwchar> <cuchar> (C++11)
Localization
<locale> <clocale>	<codecvt> (C++11/17)
Containers
<span> (C++20) <array> (C++11) <vector>	<deque> <forward_list> (C++11) <list>	<map> <set> <queue>	<unordered_map> (C++11) <unordered_set> (C++11) <stack>
Iterators
<iterator>
Ranges
<ranges> (C++20)
Algorithms
<algorithm>	<execution> (C++17)
Numerics
<complex> <random> (C++11)	<valarray> <numeric>	<bit> (C++20) <numbers> (C++20)	<cfenv> (C++11) <cmath>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<syncstream> (C++20) <spanstream> (C++23) <sstream> <fstream>	<cstdio> <cinttypes> (C++11) <strstream> (C++98/)
Regular expressions
<regex> (C++11)
Filesystem support
<filesystem> (C++17)
Thread support
<thread> (C++11) <atomic> (C++11) <mutex> (C++11)	<shared_mutex> (C++14) <condition_variable> (C++11)   <future> (C++11)	<stop_token> (C++20) <semaphore> (C++20)	<latch> (C++20) <barrier> (C++20)
C compatibility
<cstdbool> (C++11/17/20) <ccomplex> (C++11/17/20)	<ctgmath> (C++11/17/20) <cstdalign> (C++11/17/20)	<ciso646> (until C++20) <stdatomic.h>

 

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::string> (C++11)	(class template specialization)
std::hash<std::u8string> (C++20)	(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)
std::hash<std::pmr::string> (C++20)	(class template specialization)
std::hash<std::pmr::u8string> (C++20)	(class template specialization)
std::hash<std::pmr::u16string> (C++20)	(class template specialization)
std::hash<std::pmr::u32string> (C++20)	(class template specialization)
std::hash<std::pmr::wstring> (C++20)	(class template specialization)
Functions
operator+	concatenates two strings or a string and a char (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)
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 accesss
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;
  template<> struct char_traits<char>;
  template<> struct char_traits<char8_t>;
  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>
    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 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>
    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<> struct hash<string>;
  template<> struct hash<u8string>;
  template<> struct hash<u16string>;
  template<> struct hash<u32string>;
  template<> struct hash<wstring>;
  template<> struct hash<pmr::string>;
  template<> struct hash<pmr::u8string>;
  template<> struct hash<pmr::u16string>;
  template<> struct hash<pmr::u32string>;
  template<> struct hash<pmr::wstring>;
 
  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 const size_type npos  = -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());
    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());
    constexpr 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());
    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);
    constexpr 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);
    void reserve(); // deprecated
    constexpr void shrink_to_fit();
    constexpr void clear() noexcept;
    [[nodiscard]] 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);
    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);
    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);
    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);
    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;
 
    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<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>;
}