21 Strings library [strings]

21.1 General [strings.general]

This Clause describes components for manipulating sequences of any non-array POD ([basic.types]) type. In this Clause such types are called char-like types, and objects of char-like types are called char-like objects or simply characters.

The following subclauses describe a character traits class, a string class, and null-terminated sequence utilities, as summarized in Table [tab:strings.lib.summary].

Table 61 — Strings library summary
Subclause Header(s)
[char.traits] Character traits <string>
[string.classes] String classes <string>
<cctype>
<cwctype>
[c.strings] Null-terminated sequence utilities <cstring>
<cwchar>
<cstdlib>
<cuchar>

21.2 Character traits [char.traits]

This subclause defines requirements on classes representing character traits, and defines a class template char_traits<charT>, along with four specializations, char_traits<char>, char_traits<char16_t>,
char_traits<char32_t>, and char_traits<wchar_t>, that satisfy those requirements.

Most classes specified in Clauses [string.classes] and [input.output] need a set of related types and functions to complete the definition of their semantics. These types and functions are provided as a set of member typedefs and functions in the template parameter `traits' used by each such template. This subclause defines the semantics of these members.

To specialize those templates to generate a string or iostream class to handle a particular character container type CharT, that and its related character traits class Traits are passed as a pair of parameters to the string or iostream template as parameters charT and traits. Traits::char_type shall be the same as CharT.

This subclause specifies a struct template, char_traits<charT>, and four explicit specializations of it, char_traits<char>, char_traits<char16_t>, char_traits<char32_t>, and char_traits<wchar_t>, all of which appear in the header <string> and satisfy the requirements below.

21.2.1 Character traits requirements [char.traits.require]

In Table [tab:char.traits.require], X denotes a Traits class defining types and functions for the character container type CharT; c and d denote values of type CharT; p and q denote values of type const CharT*; s denotes a value of type CharT*; n, i and j denote values of type std::size_t; e and f denote values of type X::int_type; pos denotes a value of type X::pos_type; state denotes a value of type X::state_type; and r denotes an lvalue of type CharT. Operations on Traits shall not throw exceptions.

Table 62 — Character traits requirements
ExpressionReturn typeAssertion/noteComplexity
pre-/post-condition
X::char_type charT (described in [char.traits.typedefs]) compile-time
X::int_type (described in [char.traits.typedefs]) compile-time
X::off_type (described in [char.traits.typedefs]) compile-time
X::pos_type (described in [char.traits.typedefs]) compile-time
X::state_type (described in [char.traits.typedefs]) compile-time
X::eq(c,d) bool yields: whether c is to be treated as equal to d. constant
X::lt(c,d) bool yields: whether c is to be treated as less than d. constant
X::compare(p,q,n) int yields: 0 if for each i in [0,n), X::eq(p[i],q[i]) is true; else, a negative value if, for some j in [0,n), X::lt(p[j],q[j]) is true and for each i in [0,j) X::eq(p[i],q[i]) is true; else a positive value. linear
X::length(p) std::size_t yields: the smallest i such that X::eq(p[i],charT()) is true. linear
X::find(p,n,c) const X::char_type* yields: the smallest q in [p,p+n) such that X::eq(*q,c) is true, zero otherwise. linear
X::move(s,p,n) X::char_type* for each i in [0,n), performs X::assign(s[i],p[i]). Copies correctly even where the ranges [p,p+n) and [s,s+n) overlap. yields: s. linear
X::copy(s,p,n) X::char_type* pre: p not in [s,s+n). yields: s. for each i in [0,n), performs X::assign(s[i],p[i]). linear
X::assign(r,d) (not used) assigns r=d. constant
X::assign(s,n,c) X::char_type* for each i in [0,n), performs X::assign(s[i],c). yields: s. linear
X::not_eof(e) int_type yields: e if X::eq_int_type(e,X::eof()) is false, otherwise a value f such that X::eq_int_type(f,X::eof()) is false. constant
X::to_char_type(e) X::char_type yields: if for some c, X::eq_int_type(e,X::to_int_type(c)) is true, c; else some unspecified value. constant
X::to_int_type(c) X::int_type yields: some value e, constrained by the definitions of to_char_type and eq_int_type. constant
X::eq_int_type(e,f) bool yields: for all c and d, X::eq(c,d) is equal to X::eq_int_type(X::to_int_type(c), X::to_int_type(d)); otherwise, yields true if e and f are both copies of X::eof(); otherwise, yields false if one of e and f is a copy of X::eof() and the other is not; otherwise the value is unspecified. constant
X::eof() X::int_type yields: a value e such that X::eq_int_type(e,X::to_int_type(c)) is false for all values c. constant

The struct template

template<class charT> struct char_traits;

shall be provided in the header <string> as a basis for explicit specializations.

21.2.2 traits typedefs [char.traits.typedefs]

typedef CHAR_T char_type;

The type char_type is used to refer to the character container type in the implementation of the library classes defined in [string.classes] and Clause [input.output].

typedef INT_T int_type;

Requires: For a certain character container type char_type, a related container type INT_T shall be a type or class which can represent all of the valid characters converted from the corresponding char_type values, as well as an end-of-file value, eof(). The type int_type represents a character container type which can hold end-of-file to be used as a return type of the iostream class member functions.233

typedef implementation-defined off_type; typedef implementation-defined pos_type;

Requires: Requirements for off_type and pos_type are described in [iostreams.limits.pos] and [iostream.forward].

typedef STATE_T state_type;

Requires: state_type shall meet the requirements of CopyAssignable (Table [copyassignable]), CopyConstructible (Table [copyconstructible]), and DefaultConstructible (Table [defaultconstructible]) types.

If eof() can be held in char_type then some iostreams operations may give surprising results.

21.2.3 char_traits specializations [char.traits.specializations]

namespace std {
  template<> struct char_traits<char>;
  template<> struct char_traits<char16_t>;
  template<> struct char_traits<char32_t>;
  template<> struct char_traits<wchar_t>;
}

The header <string> shall define four specializations of the template struct char_traits: char_traits<char>, char_traits<char16_t>, char_traits<char32_t>, and char_traits<wchar_t>.

The requirements for the members of these specializations are given in Clause [char.traits.require].

21.2.3.1 struct char_traits<char> [char.traits.specializations.char]

namespace std {
  template<> struct char_traits<char> {
    typedef char        char_type;
    typedef int         int_type;
    typedef streamoff   off_type;
    typedef streampos   pos_type;
    typedef mbstate_t   state_type;

    static 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 int compare(const char_type* s1, const char_type* s2, size_t n);
    static size_t length(const char_type* s);
    static 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;
  };
}

The defined types for int_type, pos_type, off_type, and state_type shall be int, streampos, streamoff, and mbstate_t respectively.

The type streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].

The type streamoff shall be an implementation-defined type that satisfies the requirements for off_type in [iostreams.limits.pos] and [iostream.forward].

The type mbstate_t is defined in <cwchar> and can represent any of the conversion states that can occur in an implementation-defined set of supported multibyte character encoding rules.

The two-argument member assign shall be defined identically to the built-in operator =. The two-argument members eq and lt shall be defined identically to the built-in operators == and < for type unsigned char.

The member eof() shall return EOF.

21.2.3.2 struct char_traits<char16_t> [char.traits.specializations.char16_t]

namespace std {
  template<> struct char_traits<char16_t> {
    typedef char16_t        char_type;
    typedef uint_least16_t  int_type;
    typedef streamoff       off_type;
    typedef u16streampos    pos_type;
    typedef mbstate_t       state_type;

    static 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 int compare(const char_type* s1, const char_type* s2, size_t n);
    static size_t length(const char_type* s);
    static 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;
  };
}

The type u16streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].

The two-argument members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.

The member eof() shall return an implementation-defined constant that cannot appear as a valid UTF-16 code unit.

21.2.3.3 struct char_traits<char32_t> [char.traits.specializations.char32_t]

namespace std {
  template<> struct char_traits<char32_t> {
    typedef char32_t        char_type;
    typedef uint_least32_t  int_type;
    typedef streamoff       off_type;
    typedef u32streampos    pos_type;
    typedef mbstate_t       state_type;

    static 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 int compare(const char_type* s1, const char_type* s2, size_t n);
    static size_t length(const char_type* s);
    static 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;
  };
}

The type u32streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].

The two-argument members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.

The member eof() shall return an implementation-defined constant that cannot appear as a Unicode code point.

21.2.3.4 struct char_traits<wchar_t> [char.traits.specializations.wchar.t]

namespace std {
  template<> struct char_traits<wchar_t> {
    typedef wchar_t      char_type;
    typedef wint_t       int_type;
    typedef streamoff    off_type;
    typedef wstreampos   pos_type;
    typedef mbstate_t    state_type;

    static 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 int compare(const char_type* s1, const char_type* s2, size_t n);
    static size_t length(const char_type* s);
    static 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;
  };
}

The defined types for int_type, pos_type, and state_type shall be wint_t, wstreampos, and mbstate_t respectively.

The type wstreampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].

The type mbstate_t is defined in <cwchar> and can represent any of the conversion states that can occur in an implementation-defined set of supported multibyte character encoding rules.

The two-argument members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.

The member eof() shall return WEOF.

21.3 String classes [string.classes]

The header <string> defines the basic_string class template for manipulating varying-length sequences of char-like objects and four typedefs, string, u16string, u32string, and wstring, that name the specializations basic_string<char>, basic_string<char16_t>, basic_string<char32_t>, and basic_string<wchar_t>, respectively.

Header <string> synopsis

#include <initializer_list>

namespace std {

  // [char.traits], 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], 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);

  // [string.special], swap:
  template<class charT, class traits, class Allocator>
    void swap(basic_string<charT,traits,Allocator>& lhs,
      basic_string<charT,traits,Allocator>& rhs);

  // [string.io], 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
  typedef basic_string<char> string;
  typedef basic_string<char16_t> u16string;
  typedef basic_string<char32_t> u32string;
  typedef basic_string<wchar_t> wstring;

  // [string.conversions], 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);

  // [basic.string.hash], hash support:
  template <class T> struct hash;
  template <> struct hash<string>;
  template <> struct hash<u16string>;
  template <> struct hash<u32string>;
  template <> struct hash<wstring>;

inline namespace literals {
inline namespace string_literals {

  // [basic.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);

}
}
}

21.4 Class template basic_string [basic.string]

The class template basic_string describes objects that can store a sequence consisting of a varying number of arbitrary char-like objects with the first element of the sequence at position zero. Such a sequence is also called a “string” if the type of the char-like objects that it holds is clear from context. In the rest of this Clause, the type of the char-like objects held in a basic_string object is designated by charT.

The member functions of basic_string use an object of the Allocator class passed as a template parameter to allocate and free storage for the contained char-like objects.234

The iterators supported by basic_string are random access iterators ([random.access.iterators]).

In all cases, size() <= capacity().

The functions described in this Clause can report two kinds of errors, each associated with an exception type:

namespace std {
  template<class charT, class traits = char_traits<charT>,
    class Allocator = allocator<charT> >
  class basic_string {
  public:
    // types:
    typedef          traits                                         traits_type;
    typedef typename traits::char_type                              value_type;
    typedef          Allocator                                      allocator_type;
    typedef typename allocator_traits<Allocator>::size_type         size_type;
    typedef typename allocator_traits<Allocator>::difference_type   difference_type;

    typedef value_type& reference;
    typedef const value_type&   const_reference;
    typedef typename allocator_traits<Allocator>::pointer           pointer;
    typedef typename allocator_traits<Allocator>::const_pointer     const_pointer;

    typedef implementation-defined              iterator;       // See [container.requirements]
    typedef implementation-defined              const_iterator; // See [container.requirements]
    typedef std::reverse_iterator<iterator> reverse_iterator;
    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
    static const size_type npos = -1;

    // [string.cons], construct/copy/destroy:
    basic_string() : basic_string(Allocator()) { }
    explicit basic_string(const Allocator& a);
    basic_string(const basic_string& str);
    basic_string(basic_string&& str) noexcept;
    basic_string(const basic_string& str, size_type pos, size_type n = npos,
                 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;
    basic_string& operator=(const charT* s);
    basic_string& operator=(charT c);
    basic_string& operator=(initializer_list<charT>);

    // [string.iterators], 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;

    // [string.capacity], 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;

    // [string.access], 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();

    // [string.modifiers], modifiers:
    basic_string& operator+=(const basic_string& str);
    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(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;
    basic_string& assign(const basic_string& str, 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 pos1, 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, 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 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, 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);

    // [string.ops], string operations:
    const charT* c_str() const noexcept;
    const charT* data() const noexcept;
    allocator_type get_allocator() 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(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(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 (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(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 (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(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;
  };
}

Allocator::value_type must name the same type as charT ([string.require]).

21.4.1 basic_string general requirements [string.require]

If any operation would cause size() to exceed max_size(), that operation shall throw an exception object of type length_error.

If any member function or operator of basic_string throws an exception, that function or operator shall have no other effect.

In every specialization basic_string<charT, traits, Allocator>, the type allocator_traits<Allocator>::value_type shall name the same type as charT. Every object of type basic_string<charT, traits, Allocator> shall use an object of type Allocator to allocate and free storage for the contained charT objects as needed. The Allocator object used shall be obtained as described in [container.requirements.general].

The char-like objects in a basic_string object shall be stored contiguously. That is, for any basic_string object s, the identity &*(s.begin() + n) == &*s.begin() + n shall hold for all values of n such that 0 <= n < s.size().

References, pointers, and iterators referring to the elements of a basic_string sequence may be invalidated by the following uses of that basic_string object:

  • as an argument to any standard library function taking a reference to non-const basic_string as an argument.235

  • Calling non-const member functions, except operator[], at, front, back, begin, rbegin, end, and rend.

For example, as an argument to non-member functions swap() ([string.special]), operator>>() ([string.io]), and getline() ([string.io]), or as an argument to basic_string::swap()

21.4.2 basic_string constructors and assignment operators [string.cons]

explicit basic_string(const Allocator& a);

Effects: Constructs an object of class basic_string. The postconditions of this function are indicated in Table [tab:strings.ctr.1].

Table 63basic_string(const Allocator&) effects
ElementValue
data() a non-null pointer that is copyable and can have 0 added to it
size() 0
capacity() an unspecified value

basic_string(const basic_string& str); basic_string(basic_string&& str) noexcept;

Effects: Constructs an object of class basic_string as indicated in Table [tab:strings.ctr.cpy]. In the second form, str is left in a valid state with an unspecified value.

Table 64basic_string(const basic_string&) effects
ElementValue
data() points at the first element of an allocated copy of the array whose first element is pointed at by str.data()
size() str.size()
capacity() a value at least as large as size()

basic_string(const basic_string& str, size_type pos, size_type n = npos, const Allocator& a = Allocator());

Requires: pos <= str.size()

Throws: out_of_range if pos > str.size().

Effects: Constructs an object of class basic_string and determines the effective length rlen of the initial string value as the smaller of n and str.size() - pos, as indicated in Table [tab:strings.ctr.2].

Table 65basic_string(const basic_string&, size_type, size_type, const Allocator&) effects
ElementValue
data() points at the first element of an allocated copy of rlen consecutive elements of the string controlled by str beginning at position pos
size() rlen
capacity() a value at least as large as size()

basic_string(const charT* s, size_type n, const Allocator& a = Allocator());

Requires: s points to an array of at least n elements of charT.

Effects: Constructs an object of class basic_string and determines its initial string value from the array of charT of length n whose first element is designated by s, as indicated in Table [tab:strings.ctr.3].

Table 66basic_string(const charT*, size_type, const Allocator&) effects
ElementValue
data() points at the first element of an allocated copy of the array whose first element is pointed at by s
size() n
capacity() a value at least as large as size()

basic_string(const charT* s, const Allocator& a = Allocator());

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Constructs an object of class basic_string and determines its initial string value from the array of charT of length traits::length(s) whose first element is designated by s, as indicated in Table [tab:strings.ctr.4].

Table 67basic_string(const charT*, const Allocator&) effects
ElementValue
data() points at the first element of an allocated copy of the array whose first element is pointed at by s
size() traits::length(s)
capacity() a value at least as large as size()

Remarks: Uses traits::length().

basic_string(size_type n, charT c, const Allocator& a = Allocator());

Requires: n < npos

Effects: Constructs an object of class basic_string and determines its initial string value by repeating the char-like object c for all n elements, as indicated in Table [tab:strings.ctr.5].

Table 68basic_string(size_t, charT, const Allocator&) effects
ElementValue
data() points at the first element of an allocated array of n elements, each storing the initial value c
size() n
capacity() a value at least as large as size()

template<class InputIterator> basic_string(InputIterator begin, InputIterator end, const Allocator& a = Allocator());

Effects: If InputIterator is an integral type, equivalent to

basic_string(static_cast<size_type>(begin), static_cast<value_type>(end), a)

Otherwise constructs a string from the values in the range [begin, end), as indicated in the Sequence Requirements table (see [sequence.reqmts]).

basic_string(initializer_list<charT> il, const Allocator& a = Allocator());

Effects: Same as basic_string(il.begin(), il.end(), a).

basic_string(const basic_string& str, const Allocator& alloc); basic_string(basic_string&& str, const Allocator& alloc);

Effects: Constructs an object of class basic_string as indicated in Table [tab:strings.ctr.6]. The stored allocator is constructed from alloc. In the second form, str is left in a valid state with an unspecified value.

Table 69basic_string(const basic_string&, const Allocator&) and basic_string(basic_string&&, const Allocator&) effects
ElementValue
data() points at the first element of an allocated copy of the array whose first element is pointed at by the original value of str.data().
size() the original value of str.size()
capacity() a value at least as large as size()
get_allocator() alloc

Throws: The second form throws nothing if alloc == str.get_allocator().

basic_string& operator=(const basic_string& str);

Effects: If *this and str are not the same object, modifies *this as shown in Table [tab:strings.op=].

If *this and str are the same object, the member has no effect.

Returns: *this

Table 70operator=(const basic_string&) effects
ElementValue
data() points at the first element of an allocated copy of the array whose first element is pointed at by str.data()
size() str.size()
capacity() a value at least as large as size()

basic_string& operator=(basic_string&& str) noexcept;

Effects: If *this and str are not the same object, modifies *this as shown in Table [tab:strings.op=rv]. [ Note: A valid implementation is swap(str).  — end note ]

If *this and str are the same object, the member has no effect.

Returns: *this

Table 71operator=(basic_string&&) effects
ElementValue
data() points at the array whose first element was pointed at by str.data()
size() previous value of str.size()
capacity() a value at least as large as size()

basic_string& operator=(const charT* s);

Returns: *this = basic_string(s).

Remarks: Uses traits::length().

basic_string& operator=(charT c);

Returns: *this = basic_string(1,c).

basic_string& operator=(initializer_list<charT> il);

Effects: *this = basic_string(il).

Returns: *this.

21.4.3 basic_string iterator support [string.iterators]

iterator begin() noexcept; const_iterator begin() const noexcept; const_iterator cbegin() const noexcept;

Returns: An iterator referring to the first character in the string.

iterator end() noexcept; const_iterator end() const noexcept; const_iterator cend() const noexcept;

Returns: An iterator which is the past-the-end value.

reverse_iterator rbegin() noexcept; const_reverse_iterator rbegin() const noexcept; const_reverse_iterator crbegin() const noexcept;

Returns: An iterator which is semantically equivalent to reverse_iterator(end()).

reverse_iterator rend() noexcept; const_reverse_iterator rend() const noexcept; const_reverse_iterator crend() const noexcept;

Returns: An iterator which is semantically equivalent to reverse_iterator(begin()).

21.4.4 basic_string capacity [string.capacity]

size_type size() const noexcept;

Returns: A count of the number of char-like objects currently in the string.

Complexity: Constant time.

size_type length() const noexcept;

Returns: size().

size_type max_size() const noexcept;

Returns: The size of the largest possible string.

Complexity: Constant time.

void resize(size_type n, charT c);

Requires: n <= max_size()

Throws: length_error if n > max_size().

Effects: Alters the length of the string designated by *this as follows:

  • If n <= size(), the function replaces the string designated by *this with a string of length n whose elements are a copy of the initial elements of the original string designated by *this.

  • If n > size(), the function replaces the string designated by *this with a string of length n whose first size() elements are a copy of the original string designated by *this, and whose remaining elements are all initialized to c.

void resize(size_type n);

Effects: resize(n,charT()).

size_type capacity() const noexcept;

Returns: The size of the allocated storage in the string.

void reserve(size_type res_arg=0);

The member function reserve() is a directive that informs a basic_string object of a planned change in size, so that it can manage the storage allocation accordingly.

Effects: After reserve(), capacity() is greater or equal to the argument of reserve. [ Note: Calling reserve() with a res_arg argument less than capacity() is in effect a non-binding shrink request. A call with res_arg <= size() is in effect a non-binding shrink-to-fit request.  — end note ]

Throws: length_error if res_arg > max_size().236

void shrink_to_fit();

Remarks: shrink_to_fit is a non-binding request to reduce capacity() to size(). [ Note: The request is non-binding to allow latitude for implementation-specific optimizations.  — end note ]

void clear() noexcept;

Effects: Behaves as if the function calls:

erase(begin(), end());

bool empty() const noexcept;

Returns: size() == 0.

reserve() uses allocator_traits<Allocator>::allocate() which may throw an appropriate exception.

21.4.5 basic_string element access [string.access]

const_reference operator[](size_type pos) const; reference operator[](size_type pos);

Requires: pos <= size().

Returns: *(begin() + pos) if pos < size(). Otherwise, returns a reference to an object of type charT with value charT(), where modifying the object leads to undefined behavior.

Throws: Nothing.

Complexity: Constant time.

const_reference at(size_type pos) const; reference at(size_type pos);

Throws: out_of_range if pos >= size().

Returns: operator[](pos).

const charT& front() const; charT& front();

Requires: !empty()

Effects: Equivalent to operator[](0).

const charT& back() const; charT& back();

Requires: !empty()

Effects: Equivalent to operator[](size() - 1).

21.4.6 basic_string modifiers [string.modifiers]

21.4.6.1 basic_string::operator+= [string::op+=]

basic_string& operator+=(const basic_string& str);

Effects: Calls append(str).

Returns: *this.

basic_string& operator+=(const charT* s);

Effects: Calls append(s).

Returns: *this.

basic_string& operator+=(charT c);

Effects: Calls push_back(c);

Returns: *this.

basic_string& operator+=(initializer_list<charT> il);

Effects: Calls append(il).

Returns: *this.

21.4.6.2 basic_string::append [string::append]

basic_string& append(const basic_string& str);

Effects: Calls append(str.data(), str.size()).

Returns: *this.

basic_string& append(const basic_string& str, size_type pos, size_type n = npos);

Requires: pos <= str.size()

Throws: out_of_range if pos > str.size().

Effects: Determines the effective length rlen of the string to append as the smaller of n and str.size() - pos and calls append(str.data() + pos, rlen).

Returns: *this.

basic_string& append(const charT* s, size_type n);

Requires: s points to an array of at least n elements of charT.

Throws: length_error if size() + n > max_size().

Effects: The function replaces the string controlled by *this with a string of length size() + n whose first size() elements are a copy of the original string controlled by *this and whose remaining elements are a copy of the initial n elements of s.

Returns: *this.

basic_string& append(const charT* s);

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Calls append(s, traits::length(s)).

Returns: *this.

basic_string& append(size_type n, charT c);

Effects: Equivalent to append(basic_string(n, c)).

Returns: *this.

template<class InputIterator> basic_string& append(InputIterator first, InputIterator last);

Requires: [first,last) is a valid range.

Effects: Equivalent to append(basic_string(first, last)).

Returns: *this.

basic_string& append(initializer_list<charT> il);

Effects: Calls append(il.begin(), il.size()).

Returns: *this.

void push_back(charT c);

Effects: Equivalent to append(static_cast<size_type>(1), c).

21.4.6.3 basic_string::assign [string::assign]

basic_string& assign(const basic_string& str);

Effects: Equivalent to assign(str, 0, npos).

Returns: *this.

basic_string& assign(basic_string&& str) noexcept;

Effects: The function replaces the string controlled by *this with a string of length str.size() whose elements are a copy of the string controlled by str. [ Note: A valid implementation is swap(str).  — end note ]

Returns: *this.

basic_string& assign(const basic_string& str, size_type pos, size_type n = npos);

Requires: pos <= str.size()

Throws: out_of_range if pos > str.size().

Effects: Determines the effective length rlen of the string to assign as the smaller of n and str.size() - pos and calls assign(str.data() + pos rlen).

Returns: *this.

basic_string& assign(const charT* s, size_type n);

Requires: s points to an array of at least n elements of charT.

Throws: length_error if n > max_size().

Effects: Replaces the string controlled by *this with a string of length n whose elements are a copy of those pointed to by s.

Returns: *this.

basic_string& assign(const charT* s);

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Calls assign(s, traits::length(s)).

Returns: *this.

basic_string& assign(initializer_list<charT> il);

Effects: Calls assign(il.begin(), il.size()).

*this.

basic_string& assign(size_type n, charT c);

Effects: Equivalent to assign(basic_string(n, c)).

Returns: *this.

template<class InputIterator> basic_string& assign(InputIterator first, InputIterator last);

Effects: Equivalent to assign(basic_string(first, last)).

Returns: *this.

21.4.6.4 basic_string::insert [string::insert]

basic_string& insert(size_type pos1, const basic_string& str);

Requires: pos <= size().

Throws: out_of_range if pos > size().

Effects: Calls insert(pos, str.data(), str.size()).

Returns: *this.

basic_string& insert(size_type pos1, const basic_string& str, size_type pos2, size_type n = npos);

Requires: pos1 <= size() and pos2 <= str.size()

Throws: out_of_range if pos1 > size() or pos2 > str.size().

Effects: Determines the effective length rlen of the string to insert as the smaller of n and str.size() - pos2 and calls insert(pos1, str.data() + pos2, rlen).

Returns: *this.

basic_string& insert(size_type pos, const charT* s, size_type n);

Requires: s points to an array of at least n elements of charT and pos <= size().

Throws: out_of_range if pos > size() or length_error if size() + n > max_size().

Effects: Replaces the string controlled by *this with a string of length size() + n whose first pos elements are a copy of the initial elements of the original string controlled by *this and whose next n elements are a copy of the elements in s and whose remaining elements are a copy of the remaining elements of the original string controlled by *this.

Returns: *this.

basic_string& insert(size_type pos, const charT* s);

Requires: pos <= size() and s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Equivalent to insert(pos, s, traits::length(s)).

Returns: *this.

basic_string& insert(size_type pos, size_type n, charT c);

Effects: Equivalent to insert(pos, basic_string(n, c)).

Returns: *this.

iterator insert(const_iterator p, charT c);

Requires: p is a valid iterator on *this.

Effects: inserts a copy of c before the character referred to by p.

Returns: An iterator which refers to the copy of the inserted character.

iterator insert(const_iterator p, size_type n, charT c);

Requires: p is a valid iterator on *this.

Effects: inserts n copies of c before the character referred to by p.

Returns: An iterator which refers to the copy of the first inserted character, or p if n == 0.

template<class InputIterator> iterator insert(const_iterator p, InputIterator first, InputIterator last);

Requires: p is a valid iterator on *this. [first,last) is a valid range.

Effects: Equivalent to insert(p - begin(), basic_string(first, last)).

Returns: An iterator which refers to the copy of the first inserted character, or p if first == last.

iterator insert(const_iterator p, initializer_list<charT> il);

Effects: insert(p, il.begin(), il.end()).

Returns: An iterator which refers to the copy of the first inserted character, or p if i1 is empty.

21.4.6.5 basic_string::erase [string::erase]

basic_string& erase(size_type pos = 0, size_type n = npos);

Requires: pos <= size()

Throws: out_of_range if pos > size().

Effects: Determines the effective length xlen of the string to be removed as the smaller of n and size() - pos.

The function then replaces the string controlled by *this with a string of length size() - xlen whose first pos elements are a copy of the initial elements of the original string controlled by *this, and whose remaining elements are a copy of the elements of the original string controlled by *this beginning at position pos + xlen.

Returns: *this.

iterator erase(const_iterator p);

Throws: Nothing.

Effects: removes the character referred to by p.

Returns: An iterator which points to the element immediately following p prior to the element being erased. If no such element exists, end() is returned.

iterator erase(const_iterator first, const_iterator last);

Requires: first and last are valid iterators on *this, defining a range [first,last).

Throws: Nothing.

Effects: removes the characters in the range [first,last).

Returns: An iterator which points to the element pointed to by last prior to the other elements being erased. If no such element exists, end() is returned.

void pop_back();

Requires: !empty()

Throws: Nothing.

Effects: Equivalent to erase(size() - 1, 1).

21.4.6.6 basic_string::replace [string::replace]

basic_string& replace(size_type pos1, size_type n1, const basic_string& str);

Requires: pos1 <= size().

Throws: out_of_range if pos1 > size().

Effects: Calls replace(pos1, n1, str.data(), str.size()).

Returns: *this.

basic_string& replace(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos);

Requires: pos1 <= size() and pos2 <= str.size().

Throws: out_of_range if pos1 > size() or pos2 > str.size().

Effects: Determines the effective length rlen of the string to be inserted as the smaller of n2 and str.size() - pos2 and calls replace(pos1, n1, str.data() + pos2, rlen).

Returns: *this.

basic_string& replace(size_type pos1, size_type n1, const charT* s, size_type n2);

Requires: pos1 <= size() and s points to an array of at least n2 elements of charT.

Throws: out_of_range if pos1 > size() or length_error if the length of the resulting string would exceed max_size() (see below).

Effects: Determines the effective length xlen of the string to be removed as the smaller of n1 and size() - pos1. If size() - xlen >= max_size() - n2 throws length_error. Otherwise, the function replaces the string controlled by *this with a string of length size() - xlen + n2 whose first pos1 elements are a copy of the initial elements of the original string controlled by *this, whose next n2 elements are a copy of the initial n2 elements of s, and whose remaining elements are a copy of the elements of the original string controlled by *this beginning at position pos + xlen.

Returns: *this.

basic_string& replace(size_type pos, size_type n, const charT* s);

Requires: pos <= size() and s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Calls replace(pos, n, s, traits::length(s)).

Returns: *this.

basic_string& replace(size_type pos1, size_type n1, size_type n2, charT c);

Effects: Equivalent to replace(pos1, n1, basic_string(n2, c)).

Returns: *this.

basic_string& replace(const_iterator i1, const_iterator i2, const basic_string& str);

Requires: [begin(),i1) and [i1,i2) are valid ranges.

Effects: Calls replace(i1 - begin(), i2 - i1, str).

Returns: *this.

basic_string& replace(const_iterator i1, const_iterator i2, const charT* s, size_type n);

Requires: [begin(),i1) and [i1,i2) are valid ranges and s points to an array of at least n elements of charT.

Effects: Calls replace(i1 - begin(), i2 - i1, s, n).

Returns: *this.

basic_string& replace(const_iterator i1, const_iterator i2, const charT* s);

Requires: [begin(),i1) and [i1,i2) are valid ranges and s points to an array of at least traits::length(s) + 1 elements of charT.

Effects: Calls replace(i1 - begin(), i2 - i1, s, traits::length(s)).

Returns: *this.

basic_string& replace(const_iterator i1, const_iterator i2, size_type n, charT c);

Requires: [begin(),i1) and [i1,i2) are valid ranges.

Effects: Calls replace(i1 - begin(), i2 - i1, basic_string(n, c)).

Returns: *this.

template<class InputIterator> basic_string& replace(const_iterator i1, const_iterator i2, InputIterator j1, InputIterator j2);

Requires: [begin(),i1), [i1,i2) and [j1,j2) are valid ranges.

Effects: Calls replace(i1 - begin(), i2 - i1, basic_string(j1, j2)).

Returns: *this.

basic_string& replace(const_iterator i1, const_iterator i2, initializer_list<charT> il);

Requires: [begin(),i1) and [i1,i2) are valid ranges.

Effects: Calls replace(i1 - begin(), i2 - i1, il.begin(), il.size()).

Returns: *this.

21.4.6.7 basic_string::copy [string::copy]

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

Requires: pos <= size()

Throws: out_of_range if pos > size().

Effects: Determines the effective length rlen of the string to copy as the smaller of n and size() - pos. s shall designate an array of at least rlen elements.

The function then replaces the string designated by s with a string of length rlen whose elements are a copy of the string controlled by *this beginning at position pos.

The function does not append a null object to the string designated by s.

Returns: rlen.

21.4.6.8 basic_string::swap [string::swap]

void swap(basic_string& s);

Postcondition: *this contains the same sequence of characters that was in s, s contains the same sequence of characters that was in *this.

Throws: Nothing.

Complexity: Constant time.

21.4.7 basic_string string operations [string.ops]

21.4.7.1 basic_string accessors [string.accessors]

const charT* c_str() const noexcept; const charT* data() const noexcept;

Returns: A pointer p such that p + i == &operator[](i) for each i in [0,size()].

Complexity: Constant time.

Requires: The program shall not alter any of the values stored in the character array.

allocator_type get_allocator() const noexcept;

Returns: A copy of the Allocator object used to construct the string or, if that allocator has been replaced, a copy of the most recent replacement.

21.4.7.2 basic_string::find [string::find]

size_type find(const basic_string& str, size_type pos = 0) const noexcept;

Effects: Determines the lowest position xpos, if possible, such that both of the following conditions obtain:

  • pos <= xpos and xpos + str.size() <= size();

  • traits::eq(at(xpos+I), str.at(I)) for all elements I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type find(const charT* s, size_type pos, size_type n) const;

Returns: find(basic_string(s,n),pos).

size_type find(const charT* s, size_type pos = 0) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: find(basic_string(s), pos).

size_type find(charT c, size_type pos = 0) const;

Returns: find(basic_string(1,c), pos).

21.4.7.3 basic_string::rfind [string::rfind]

size_type rfind(const basic_string& str, size_type pos = npos) const noexcept;

Effects: Determines the highest position xpos, if possible, such that both of the following conditions obtain:

  • xpos <= pos and xpos + str.size() <= size();

  • traits::eq(at(xpos+I), str.at(I)) for all elements I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type rfind(const charT* s, size_type pos, size_type n) const;

Returns: rfind(basic_string(s, n), pos).

size_type rfind(const charT* s, size_type pos = npos) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: rfind(basic_string(s), pos).

size_type rfind(charT c, size_type pos = npos) const;

Returns: rfind(basic_string(1,c),pos).

21.4.7.4 basic_string::find_first_of [string::find.first.of]

size_type find_first_of(const basic_string& str, size_type pos = 0) const noexcept;

Effects: Determines the lowest position xpos, if possible, such that both of the following conditions obtain:

  • pos <= xpos and xpos < size();

  • traits::eq(at(xpos), str.at(I)) for some element I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type find_first_of(const charT* s, size_type pos, size_type n) const;

Returns: find_first_of(basic_string(s, n), pos).

size_type find_first_of(const charT* s, size_type pos = 0) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: find_first_of(basic_string(s), pos).

size_type find_first_of(charT c, size_type pos = 0) const;

Returns: find_first_of(basic_string(1,c), pos).

21.4.7.5 basic_string::find_last_of [string::find.last.of]

size_type find_last_of(const basic_string& str, size_type pos = npos) const noexcept;

Effects: Determines the highest position xpos, if possible, such that both of the following conditions obtain:

  • xpos <= pos and xpos < size();

  • traits::eq(at(xpos), str.at(I)) for some element I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type find_last_of(const charT* s, size_type pos, size_type n) const;

Returns: find_last_of(basic_string(s, n), pos).

size_type find_last_of(const charT* s, size_type pos = npos) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: find_last_of(basic_string(s), pos).

size_type find_last_of(charT c, size_type pos = npos) const;

Returns: find_last_of(basic_string(1,c),pos).

21.4.7.6 basic_string::find_first_not_of [string::find.first.not.of]

size_type find_first_not_of(const basic_string& str, size_type pos = 0) const noexcept;

Effects: Determines the lowest position xpos, if possible, such that both of the following conditions obtain:

  • pos <= xpos and xpos < size();

  • traits::eq(at(xpos), str.at(I)) for no element I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type find_first_not_of(const charT* s, size_type pos, size_type n) const;

Returns: find_first_not_of(basic_string(s, n), pos).

size_type find_first_not_of(const charT* s, size_type pos = 0) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: find_first_not_of(basic_string(s), pos).

size_type find_first_not_of(charT c, size_type pos = 0) const;

Returns: find_first_not_of(basic_string(1, c), pos).

21.4.7.7 basic_string::find_last_not_of [string::find.last.not.of]

size_type find_last_not_of(const basic_string& str, size_type pos = npos) const noexcept;

Effects: Determines the highest position xpos, if possible, such that both of the following conditions obtain:

  • xpos <= pos and xpos < size();

  • traits::eq(at(xpos), str.at(I)) for no element I of the string controlled by str.

Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.

Remarks: Uses traits::eq().

size_type find_last_not_of(const charT* s, size_type pos, size_type n) const;

Returns: find_last_not_of(basic_string(s, n), pos).

size_type find_last_not_of(const charT* s, size_type pos = npos) const;

Requires: s points to an array of at least traits::length(s) + 1 elements of charT.

Returns: find_last_not_of(basic_string(s), pos).

size_type find_last_not_of(charT c, size_type pos = npos) const;

Returns: find_last_not_of(basic_string(1, c), pos).

21.4.7.8 basic_string::substr [string::substr]

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

Requires: pos <= size()

Throws: out_of_range if pos > size().

Effects: Determines the effective length rlen of the string to copy as the smaller of n and size() - pos.

Returns: basic_string(data()+pos,rlen).

21.4.7.9 basic_string::compare [string::compare]

int compare(const basic_string& str) const noexcept;

Effects: Determines the effective length rlen of the strings to compare as the smallest of size() and str.size(). The function then compares the two strings by calling traits::compare(data(), str.data(), rlen).

Returns: The nonzero result if the result of the comparison is nonzero. Otherwise, returns a value as indicated in Table [tab:strings.compare].

Table 72compare() results
ConditionReturn Value
size() < str.size() < 0
size() == str.size() 0
size() > str.size() > 0

int compare(size_type pos1, size_type n1, const basic_string& str) const;

Returns: basic_string(*this,pos1,n1).compare(str).

int compare(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos) const;

Returns: basic_string(*this, pos1, n1).compare(basic_string(str, pos2, n2)).

int compare(const charT* s) const;

Returns: compare(basic_string(s)).

int compare(size_type pos, size_type n1, const charT* s) const;

Returns: basic_string(*this, pos, n1).compare(basic_string(s)).

int compare(size_type pos, size_type n1, const charT* s, size_type n2) const;

Returns: basic_string(*this, pos, n1).compare(basic_string(s, n2)).

21.4.8 basic_string non-member functions [string.nonmembers]

21.4.8.1 operator+ [string::op+]

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);

Returns: basic_string<charT,traits,Allocator>(lhs).append(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);

Returns: std::move(lhs.append(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);

Returns: std::move(rhs.insert(0, lhs))

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);

Returns: std::move(lhs.append(rhs))Note: Or equivalently std::move(rhs.insert(0, lhs))  — end note ]

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: basic_string<charT,traits,Allocator>(lhs) + rhs.

Remarks: Uses traits::length().

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(const charT* lhs, basic_string<charT,traits,Allocator>&& rhs);

Returns: std::move(rhs.insert(0, lhs)).

Remarks: Uses traits::length().

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(charT lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: basic_string<charT,traits,Allocator>(1,lhs) + rhs.

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(charT lhs, basic_string<charT,traits,Allocator>&& rhs);

Returns: std::move(rhs.insert(0, 1, lhs)).

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Returns: lhs + basic_string<charT,traits,Allocator>(rhs).

Remarks: Uses traits::length().

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(basic_string<charT,traits,Allocator>&& lhs, const charT* rhs);

Returns: std::move(lhs.append(rhs)).

Remarks: Uses traits::length().

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(const basic_string<charT,traits,Allocator>& lhs, charT rhs);

Returns: lhs + basic_string<charT,traits,Allocator>(1,rhs).

template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+(basic_string<charT,traits,Allocator>&& lhs, charT rhs);

Returns: std::move(lhs.append(1, rhs)).

21.4.8.2 operator== [string::operator==]

template<class charT, class traits, class Allocator> bool operator==(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: lhs.compare(rhs) == 0.

template<class charT, class traits, class Allocator> bool operator==(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs == lhs.

template<class charT, class traits, class Allocator> bool operator==(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Requires: rhs points to an array of at least traits::length(rhs) + 1 elements of charT.

Returns: lhs.compare(rhs) == 0.

21.4.8.3 operator!= [string::op!=]

template<class charT, class traits, class Allocator> bool operator!=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: !(lhs == rhs).

template<class charT, class traits, class Allocator> bool operator!=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs != lhs.

template<class charT, class traits, class Allocator> bool operator!=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Requires: rhs points to an array of at least traits::length(rhs) + 1 elements of charT.

Returns: lhs.compare(rhs) != 0.

21.4.8.4 operator< [string::op<]

template<class charT, class traits, class Allocator> bool operator< (const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: lhs.compare(rhs) < 0.

template<class charT, class traits, class Allocator> bool operator< (const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs.compare(lhs) > 0.

template<class charT, class traits, class Allocator> bool operator< (const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Returns: lhs.compare(rhs) < 0.

21.4.8.5 operator> [string::op>]

template<class charT, class traits, class Allocator> bool operator> (const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: lhs.compare(rhs) > 0.

template<class charT, class traits, class Allocator> bool operator> (const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs.compare(lhs) < 0.

template<class charT, class traits, class Allocator> bool operator> (const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Returns: lhs.compare(rhs) > 0.

21.4.8.6 operator<= [string::op<=]

template<class charT, class traits, class Allocator> bool operator<=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: lhs.compare(rhs) <= 0.

template<class charT, class traits, class Allocator> bool operator<=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs.compare(lhs) >= 0.

template<class charT, class traits, class Allocator> bool operator<=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Returns: lhs.compare(rhs) <= 0.

21.4.8.7 operator>= [string::op>=]

template<class charT, class traits, class Allocator> bool operator>=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs) noexcept;

Returns: lhs.compare(rhs) >= 0.

template<class charT, class traits, class Allocator> bool operator>=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs);

Returns: rhs.compare(lhs) <= 0.

template<class charT, class traits, class Allocator> bool operator>=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs);

Returns: lhs.compare(rhs) >= 0.

21.4.8.8 swap [string.special]

template<class charT, class traits, class Allocator> void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>& rhs);

Effects: Equivalent to lhs.swap(rhs);

21.4.8.9 Inserters and extractors [string.io]

template<class charT, class traits, class Allocator> basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>& is, basic_string<charT,traits,Allocator>& str);

Effects: Behaves as a formatted input function ([istream.formatted.reqmts]). After constructing a sentry object, if the sentry converts to true, calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1,c). If is.width() is greater than zero, the maximum number n of characters appended is is.width(); otherwise n is str.max_size(). Characters are extracted and appended until any of the following occurs:

  • n characters are stored;

  • end-of-file occurs on the input sequence;

  • isspace(c,is.getloc()) is true for the next available input character c.

After the last character (if any) is extracted, is.width(0) is called and the sentry object k is destroyed.

If the function extracts no characters, it calls is.setstate(ios::failbit), which may throw ios_base::failure ([iostate.flags]).

Returns: is

template<class charT, class traits, class Allocator> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const basic_string<charT,traits,Allocator>& str);

Effects: Behaves as a formatted output function ([ostream.formatted.reqmts]) of os. Forms a character sequence seq, initially consisting of the elements defined by the range [str.begin(), str.end()). Determines padding for seq as described in [ostream.formatted.reqmts]. Then inserts seq as if by calling os.rdbuf()->sputn(seq, n), where n is the larger of os.width() and str.size(); then calls os.width(0).

Returns: os

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);

Effects: Behaves as an unformatted input function ([istream.unformatted]), except that it does not affect the value returned by subsequent calls to basic_istream<>::gcount(). After constructing a sentry object, if the sentry converts to true, calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1, c) until any of the following occurs:

  • end-of-file occurs on the input sequence (in which case, the getline function calls is.setstate(ios_base::eofbit)).

  • traits::eq(c, delim) for the next available input character c (in which case, c is extracted but not appended) ([iostate.flags])

  • str.max_size() characters are stored (in which case, the function calls is.setstate(ios_base::failbit)) ([iostate.flags])

The conditions are tested in the order shown. In any case, after the last character is extracted, the sentry object k is destroyed.

If the function extracts no characters, it calls is.setstate(ios_base::failbit) which may throw ios_base::failure ([iostate.flags]).

Returns: is.

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);

Returns: getline(is,str,is.widen('\n'))

21.5 Numeric conversions [string.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);

Effects: the first two functions call strtol(str.c_str(), ptr, base), and the last three functions call strtoul(str.c_str(), ptr, base), strtoll(str.c_str(), ptr, base), and strtoull(str.c_str(), ptr, base), respectively. Each function returns the converted result, if any. The argument ptr designates a pointer to an object internal to the function that is used to determine what to store at *idx. If the function does not throw an exception and idx != 0, the function stores in *idx the index of the first unconverted element of str.

Returns: The converted result.

Throws: invalid_argument if strtol, strtoul, strtoll, or strtoull reports that no conversion could be performed. Throws out_of_range if strtol, strtoul, strtoll or strtoull sets errno to ERANGE, or if the converted value is outside the range of representable values for the return type.

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);

Effects: the first two functions call strtod(str.c_str(), ptr) and the third function calls strtold(str.c_str(), ptr). Each function returns the converted result, if any. The argument ptr designates a pointer to an object internal to the function that is used to determine what to store at *idx. If the function does not throw an exception and idx != 0, the function stores in *idx the index of the first unconverted element of str.

Returns: The converted result.

Throws: invalid_argument if strtod or strtold reports that no conversion could be performed. Throws out_of_range if strtod or strtold sets errno to ERANGE or if the converted value is outside the range of representable values for the return type.

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);

Returns: Each function returns a string object holding the character representation of the value of its argument that would be generated by calling sprintf(buf, fmt, val) with a format specifier of "%d", "%u", "%ld", "%lu", "%lld", "%llu", "%f", "%f", or "%Lf", respectively, where buf designates an internal character buffer of sufficient size.

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);

Effects: the first two functions call wcstol(str.c_str(), ptr, base), and the last three functions call wcstoul(str.c_str(), ptr, base), wcstoll(str.c_str(), ptr, base), and wcstoull(str.c_str(), ptr, base), respectively. Each function returns the converted result, if any. The argument ptr designates a pointer to an object internal to the function that is used to determine what to store at *idx. If the function does not throw an exception and idx != 0, the function stores in *idx the index of the first unconverted element of str.

Returns: The converted result.

Throws: invalid_argument if wcstol, wcstoul, wcstoll, or wcstoull reports that no conversion could be performed. Throws out_of_range if the converted value is outside the range of representable values for the return type.

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);

Effects: the first two functions call wcstod(str.c_str(), ptr) and the third function calls wcstold(str.c_str(), ptr). Each function returns the converted result, if any. The argument ptr designates a pointer to an object internal to the function that is used to determine what to store at *idx. If the function does not throw an exception and idx != 0, the function stores in *idx the index of the first unconverted element of str.

Returns: The converted result.

Throws: invalid_argument if wcstod or wcstold reports that no conversion could be performed. Throws out_of_range if wcstod or wcstold sets errno to ERANGE.

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);

Returns: Each function returns a wstring object holding the character representation of the value of its argument that would be generated by calling swprintf(buf, buffsz, fmt, val) with a format specifier of L"%d", L"%u", L"%ld", L"%lu", L"%lld", L"%llu", L"%f", L"%f", or L"%Lf", respectively, where buf designates an internal character buffer of sufficient size buffsz.

21.6 Hash support [basic.string.hash]

template <> struct hash<string>; template <> struct hash<u16string>; template <> struct hash<u32string>; template <> struct hash<wstring>;

The template specializations shall meet the requirements of class template hash ([unord.hash]).

21.7 Suffix for basic_string literals [basic.string.literals]

string operator "" s(const char* str, size_t len);

Returns: string{str,len}

u16string operator "" s(const char16_t* str, size_t len);

Returns: u16string{str,len}

u32string operator "" s(const char32_t* str, size_t len);

Returns: u32string{str,len}

wstring operator "" s(const wchar_t* str, size_t len);

Returns: wstring{str,len}

Note: The same suffix s is used for chrono::duration literals denoting seconds but there is no conflict, since duration suffixes apply to numbers and string literal suffixes apply to character array literals.  — end note ]

21.8 Null-terminated sequence utilities [c.strings]

Tables [tab:strings.hdr.cctype], [tab:strings.hdr.cwctype], [tab:strings.hdr.cstring], [tab:strings.hdr.cwchar], [tab:strings.hdr.cstdlib], and [tab:strings.hdr.cuchar] describe headers <cctype>, <cwctype>, <cstring>, <cwchar>, <cstdlib> (character conversions), and <cuchar>, respectively.

The contents of these headers shall be the same as the Standard C Library headers <ctype.h>, <wctype.h>, <string.h>, <wchar.h>, and <stdlib.h> and the C Unicode TR header <uchar.h>, respectively, with the following modifications:

The headers shall not define the types char16_t, char32_t, and wchar_t ([lex.key]).

The function signature strchr(const char*, int) shall be replaced by the two declarations:

const char* strchr(const char* s, int c);
      char* strchr(      char* s, int c);

both of which shall have the same behavior as the original declaration.

The function signature strpbrk(const char*, const char*) shall be replaced by the two declarations:

const char* strpbrk(const char* s1, const char* s2);
      char* strpbrk(      char* s1, const char* s2);

both of which shall have the same behavior as the original declaration.

The function signature strrchr(const char*, int) shall be replaced by the two declarations:

const char* strrchr(const char* s, int c);
      char* strrchr(      char* s, int c);

both of which shall have the same behavior as the original declaration.

The function signature strstr(const char*, const char*) shall be replaced by the two declarations:

const char* strstr(const char* s1, const char* s2);
      char* strstr(      char* s1, const char* s2);

both of which shall have the same behavior as the original declaration.

The function signature memchr(const void*, int, size_t) shall be replaced by the two declarations:

const void* memchr(const void* s, int c, size_t n);
      void* memchr(      void* s, int c, size_t n);

both of which shall have the same behavior as the original declaration.

The function signature wcschr(const wchar_t*, wchar_t) shall be replaced by the two declarations:

const wchar_t* wcschr(const wchar_t* s, wchar_t c);
      wchar_t* wcschr(      wchar_t* s, wchar_t c);

both of which shall have the same behavior as the original declaration.

The function signature wcspbrk(const wchar_t*, const wchar_t*) shall be replaced by the two declarations:

const wchar_t* wcspbrk(const wchar_t* s1, const wchar_t* s2);
      wchar_t* wcspbrk(      wchar_t* s1, const wchar_t* s2);

both of which shall have the same behavior as the original declaration.

The function signature wcsrchr(const wchar_t*, wchar_t) shall be replaced by the two declarations:

const wchar_t* wcsrchr(const wchar_t* s, wchar_t c);
      wchar_t* wcsrchr(      wchar_t* s, wchar_t c);

both of which shall have the same behavior as the original declaration.

The function signature wcsstr(const wchar_t*, const wchar_t*) shall be replaced by the two declarations:

const wchar_t* wcsstr(const wchar_t* s1, const wchar_t* s2);
      wchar_t* wcsstr(      wchar_t* s1, const wchar_t* s2);

both of which shall have the same behavior as the original declaration.

The function signature wmemchr(const wwchar_t*, int, size_t) shall be replaced by the two declarations:

const wchar_t* wmemchr(const wchar_t* s, wchar_t c, size_t n);
      wchar_t* wmemchr(      wchar_t* s, wchar_t c, size_t n);

both of which shall have the same behavior as the original declaration.

The functions strerror and strtok are not required to avoid data races ([res.on.data.races]).

Calling the functions listed in Table [tab:mbstate.data.races] with an mbstate_t* argument of NULL may introduce a data race ([res.on.data.races]) with other calls to these functions with an mbstate_t* argument of NULL.

Table 73 — Potential mbstate_t data races
mbrlen mbrtowc mbsrtowc mbtowc wcrtomb
wcsrtomb wctomb

See also: ISO C 7.3, 7.10.7, 7.10.8, and 7.11. Amendment 1 4.4, 4.5, and 4.6.

Table 74 — Header <cctype> synopsis
TypeName(s)
Functions:
isalnum isblank isdigit isprint isupper
tolower isalpha isgraph ispunct isxdigit
toupper iscntrl islower isspace
Table 75 — Header <cwctype> synopsis
TypeName(s)
Macro: WEOF
Types: wctrans_t wctype_t wint_t
Functions:
iswalnum iswctype iswprint iswxdigit wctrans
iswalpha iswdigit iswpunct towctrans wctype
iswblank iswgraph iswspace towlower
iswcntrl iswlower iswupper towupper
Table 76 — Header <cstring> synopsis
TypeName(s)
Macro: NULL <cstring>
Type: size_t <cstring>
Functions:
memchr strcat strcspn strncpy strtok
memcmp strchr strerror strpbrk strxfrm
memcpy strcmp strlen strrchr
memmove strcoll strncat strspn
memset strcpy strncmp strstr
Table 77 — Header <cwchar> synopsis
TypeName(s)
Macros: NULL WCHAR_MAX WCHAR_MIN WEOF
Types: mbstate_t wint_t size_t tm
Functions:
btowc mbsinit vwscanf wcsncpy wcstoull
fgetwc mbsrtowcs wcrtomb wcspbrk wcstoul
fgetws putwchar wcscat wcsrchr wcsxfrm
fputwc putwc wcschr wcsrtombs wctob
fputws swprintf wcscmp wcsspn wmemchr
fwide swscanf wcscoll wcsstr wmemcmp
fwprintf ungetwc wcscpy wcstod wmemcpy
fwscanf vfwprintf wcscspn wcstof wmemmove
getwchar vfwscanf wcsftime wcstok wmemset
getwc vswprintf wcslen wcstold wprintf
mbrlen vswscanf wcsncat wcstoll wscanf
mbrtowc vwprintf wcsncmp wcstol
Table 78 — Header <cstdlib> synopsis
TypeName(s)
Macros: MB_CUR_MAX
Functions:
atof mblen strtof strtoul
atoi mbtowc strtol strtoull
atol mbstowcs strtold wctomb
atoll strtod strtoll wcstombs
Table 79 — Header <cuchar> synopsis
TypeName(s)
Macros: __STDC_UTF_16__
__STDC_UTF_32__
Functions: mbrtoc16 c16rtomb
mbrtoc32 c32rtomb