[basic.string] (original) (raw)

21 Strings library [strings]

21.3 String classes [string.classes]

21.3.2 Class template basic_­string [basic.string]

The class templatebasic_­stringdescribes 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.

In all cases,[data(), data() + size()] is a valid range,data() + size() points at an object with value charT()(a “null terminator”), and size() <= capacity() is true.

namespace std { template<class charT, class traits = char_traits, class Allocator = allocator> class basic_string { public:

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;


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(size_type n, charT c, const Allocator& a = Allocator());
template<class InputIterator>
  constexpr basic_string(InputIterator begin, InputIterator 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=(charT c);
constexpr basic_string& operator=(initializer_list<charT>);


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;


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);
constexpr size_type capacity() const noexcept;
constexpr void reserve(size_type res_arg);
constexpr void shrink_to_fit();
constexpr void clear() noexcept;
[[nodiscard]] constexpr bool empty() const noexcept;


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();


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 InputIterator>
  constexpr basic_string& append(InputIterator first, InputIterator 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 InputIterator>
  constexpr basic_string& assign(InputIterator first, InputIterator 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 InputIterator>
  constexpr iterator insert(const_iterator p, InputIterator first, InputIterator 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 InputIterator>
  constexpr basic_string& replace(const_iterator i1, const_iterator i2,
                                  InputIterator j1, InputIterator 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);


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 below);
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 below);
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 below);
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 below);
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 below);
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 below);
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 below);
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;

};

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

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

template<class charT, class traits, class Allocator = allocator> basic_string(basic_string_view<charT, traits>, typename see below::size_type, typename see below::size_type, const Allocator& = Allocator()) -> basic_string<charT, traits, Allocator>; }

A size_­type parameter type in a basic_­string deduction guide refers to the size_­type member type of the type deduced by the deduction guide.

21.3.2.1 General requirements [string.require]

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

If any member function or operator of basic_­string throws an exception, that function or operator has no other effect on the basic_­string object.

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 typebasic_­string<charT, traits, Allocator> uses an object of typeAllocator to allocate and free storage for the contained charTobjects as needed.

In every specialization basic_­string<charT, traits, Allocator>, the type traits shall meet the character traits requirements ([char.traits]).

[ Note

:

The program is ill-formed if traits​::​char_­typeis not the same type as charT.

— end note

]

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

• Passing as an argument to any standard library function taking a reference to non-constbasic_­string as an argument.222
• Calling non-const member functions, exceptoperator[],at,data,front,back,begin,rbegin,end, andrend.

21.3.2.2 Constructors and assignment operators [string.cons]

constexpr explicit basic_string(const Allocator& a) noexcept;

Postconditions: size() is equal to 0.

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

Effects:Constructs an object whose value is that of str prior to this call.

Remarks:In the second form, str is left in a valid but unspecified state.

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());

Effects:Let n be npos for the first overload.

Equivalent to:

basic_string(basic_string_view<charT, traits>(str).substr(pos, n), a)

template<class T> constexpr basic_string(const T& t, size_type pos, size_type n, const Allocator& a = Allocator());

Constraints: is_­convertible_­v<const T&, basic_­string_­view<charT, traits>>is true.

Effects:Creates a variable, sv, as if by basic_­string_­view<charT, traits> sv = t;and then behaves the same as:

basic_string(sv.substr(pos, n), a);

template<class T> constexpr explicit basic_string(const T& t, const Allocator& a = Allocator());

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Creates a variable, sv, as if bybasic_­string_­view<charT, traits> sv = t; and then behaves the same as basic_­string(sv.data(), sv.size(), a).

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

Preconditions: [s, s + n) is a valid range.

Effects:Constructs an object whose initial value is the range [s, s + n).

Postconditions: size() is equal to n, andtraits​::​compare(data(), s, n) is equal to 0.

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

[ Note

:

This affects class template argument deduction.

— end note

]

Effects:Equivalent to: basic_­string(s, traits​::​length(s), a).

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

[ Note

:

This affects class template argument deduction.

— end note

]

Effects:Constructs an object whose value consists of n copies of c.

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

Effects:Constructs a string from the values in the range [begin, end), as indicated in Table 77.

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

Effects:Equivalent to basic_­string(il.begin(), il.end(), a).

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

Effects:Constructs an object whose value is that of str prior to this call.

The stored allocator is constructed from alloc.

In the second form, str is left in a valid but unspecified state.

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

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

Constraints: InputIterator is a type that qualifies as an input iterator, and Allocator is a type that qualifies as an allocator ([container.requirements.general]).

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 below::size_type, typename see below::size_type,const Allocator& = Allocator()) -> basic_string<charT, traits, Allocator>;

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

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

Otherwise, replaces the value of *this with a copy of 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);

Effects:Move assigns as a sequence container, except that iterators, pointers and references may be invalidated.

template<class T> constexpr basic_string& operator=(const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>>is true and
• is_­convertible_­v<const T&, const charT*>is false.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return assign(sv);

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

Effects:Equivalent to:return *this = basic_­string_­view<charT, traits>(s);

constexpr basic_string& operator=(charT c);

Effects:Equivalent to:

return *this = basic_string_view<charT, traits>(addressof(c), 1);

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

Effects:Equivalent to:

return *this = basic_string_view<charT, traits>(il.begin(), il.size());

21.3.2.3 Iterator support [string.iterators]

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

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

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

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

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

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

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

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

21.3.2.4 Capacity [string.capacity]

constexpr size_type size() const noexcept;constexpr size_type length() const noexcept;

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

Complexity:Constant time.

constexpr size_type max_size() const noexcept;

Returns:The largest possible number of char-like objects that can be stored in abasic_­string.

Complexity:Constant time.

constexpr void resize(size_type n, charT c);

Effects:Alters the value of*thisas follows:

• Ifn <= size(), erases the last size() - n elements.
• Ifn > size(), appends n - size() copies of c.

constexpr void resize(size_type n);

Effects:Equivalent to resize(n, charT()).

constexpr size_type capacity() const noexcept;

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

Complexity:Constant time.

constexpr void reserve(size_type res_arg);

Effects:A directive that informs a basic_­string of a planned change in size, so that the storage allocation can be managed accordingly.

Afterreserve(),capacity()is greater or equal to the argument ofreserveif reallocation happens; and equal to the previous value ofcapacity()otherwise.

Reallocation happens at this point if and only if the current capacity is less than the argument of reserve().

Throws: length_­errorifres_­arg > max_­size() or any exceptions thrown byallocator_­traits <Allocator>​::​allocate.

constexpr void shrink_to_fit();

Effects: shrink_­to_­fit is a non-binding request to reducecapacity() to size().

[ Note

:

The request is non-binding to allow latitude for implementation-specific optimizations.

— end note

]

It does not increase capacity(), but may reduce capacity()by causing reallocation.

Complexity:If the size is not equal to the old capacity, linear in the size of the sequence; otherwise constant.

Remarks:Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence, as well as the past-the-end iterator.

[ Note

:

If no reallocation happens, they remain valid.

— end note

]

constexpr void clear() noexcept;

Effects:Equivalent to: erase(begin(), end());

[[nodiscard]] constexpr bool empty() const noexcept;

Effects:Equivalent to:return size() == 0;

21.3.2.5 Element access [string.access]

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

Preconditions: pos <= size().

Returns: *(begin() + pos) if pos < size().

Otherwise, returns a reference to an object of type charT with valuecharT(), where modifying the object to any value other thancharT() leads to undefined behavior.

Complexity:Constant time.

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

Throws: out_­of_­rangeifpos >= size().

Returns: operator[](pos).

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

Effects:Equivalent to: return operator[](0);

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

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

21.3.2.6 Modifiers [string.modifiers]

21.3.2.6.1 basic_­string​::​operator+= [string.op.append]

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

Effects:Equivalent to: return append(str);

template<class T> constexpr basic_string& operator+=(const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return append(sv);

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

Effects:Equivalent to: return append(s);

constexpr basic_string& operator+=(charT c);

Effects:Equivalent to: return append(size_­type{1}, c);

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

Effects:Equivalent to: return append(il);

21.3.2.6.2 basic_­string​::​append [string.append]

constexpr basic_string& append(const basic_string& str);

Effects:Equivalent to: return append(str.data(), str.size());

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

Effects:Equivalent to:

return append(basic_string_view<charT, traits>(str).substr(pos, n));

template<class T> constexpr basic_string& append(const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return append(sv.data(), sv.size());

template<class T> constexpr basic_string& append(const T& t, size_type pos, size_type n = npos);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return append(sv.substr(pos, n));

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

Preconditions: [s, s + n) is a valid range.

Effects:Appends a copy of the range [s, s + n) to the string.

constexpr basic_string& append(const charT* s);

Effects:Equivalent to: return append(s, traits​::​length(s));

constexpr basic_string& append(size_type n, charT c);

Effects:Appends n copies of c to the string.

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

Effects:Equivalent to: return append(basic_­string(first, last, get_­allocator()));

constexpr basic_string& append(initializer_list<charT> il);

Effects:Equivalent to: return append(il.begin(), il.size());

constexpr void push_back(charT c);

Effects:Equivalent toappend(size_­type{1}, c).

21.3.2.6.3 basic_­string​::​assign [string.assign]

constexpr basic_string& assign(const basic_string& str);

Effects:Equivalent to: return *this = 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);

Effects:Equivalent to: return *this = std​::​move(str);

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

Effects:Equivalent to:

return assign(basic_string_view<charT, traits>(str).substr(pos, n));

template<class T> constexpr basic_string& assign(const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return assign(sv.data(), sv.size());

template<class T> constexpr basic_string& assign(const T& t, size_type pos, size_type n = npos);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return assign(sv.substr(pos, n));

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

Preconditions: [s, s + n) is a valid range.

Effects:Replaces the string controlled by *this with a copy of the range [s, s + n).

constexpr basic_string& assign(const charT* s);

Effects:Equivalent to: return assign(s, traits​::​length(s));

constexpr basic_string& assign(initializer_list<charT> il);

Effects:Equivalent to: return assign(il.begin(), il.size());

constexpr basic_string& assign(size_type n, charT c);

Effects:Equivalent to:

clear(); resize(n, c); return *this;

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

Effects:Equivalent to: return assign(basic_­string(first, last, get_­allocator()));

21.3.2.6.4 basic_­string​::​insert [string.insert]

constexpr basic_string& insert(size_type pos, const basic_string& str);

Effects:Equivalent to: return insert(pos, str.data(), str.size());

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

Effects:Equivalent to:

return insert(pos1, basic_string_view<charT, traits>(str), pos2, n);

template<class T> constexpr basic_string& insert(size_type pos, const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return insert(pos, sv.data(), sv.size());

template<class T> constexpr basic_string& insert(size_type pos1, const T& t, size_type pos2, size_type n = npos);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return insert(pos1, sv.substr(pos2, n));

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

Preconditions: [s, s + n) is a valid range.

Throws:

• out_­of_­range if pos > size(),
• length_­error if n > max_­size() - size(), or
• any exceptions thrown by allocator_­traits<Allocator>​::​allocate.

Effects:Inserts a copy of the range [s, s + n)immediately before the character at position pos if pos < size(), or otherwise at the end of the string.

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

Effects:Equivalent to: return insert(pos, s, traits​::​length(s));

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

Effects:Inserts n copies of c before the character at position posif pos < size(), or otherwise at the end of the string.

Throws:

• out_­of_­range if pos > size(),
• length_­error if n > max_­size() - size(), or
• any exceptions thrown by allocator_­traits<Allocator>​::​allocate.

constexpr iterator insert(const_iterator p, charT c);

Preconditions: p is a valid iterator on*this.

Effects:Inserts a copy of c at the position p.

Returns:An iterator which refers to the inserted character.

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

Preconditions: p is a valid iterator on*this.

Effects:Inserts n copies of c at the position p.

Returns:An iterator which refers to the first inserted character, orp if n == 0.

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

Preconditions: p is a valid iterator on*this.

Effects:Equivalent toinsert(p - begin(), basic_­string(first, last, get_­allocator())).

Returns:An iterator which refers to the first inserted character, orp if first == last.

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

Effects:Equivalent to: return insert(p, il.begin(), il.end());

21.3.2.6.5 basic_­string​::​erase [string.erase]

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

Throws: out_­of_­rangeif pos > size().

Effects:Determines the effective length xlenof the string to be removed as the smaller of n andsize() - pos.

Removes the characters in the range [begin() + pos, begin() + pos + xlen).

constexpr iterator erase(const_iterator p);

Preconditions: p is a valid dereferenceable iterator on *this.

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.

constexpr iterator erase(const_iterator first, const_iterator last);

Preconditions: first and last are valid iterators on*this.

[first, last) is a valid range.

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.

constexpr void pop_back();

Effects:Equivalent to erase(end() - 1).

21.3.2.6.6 basic_­string​::​replace [string.replace]

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

Effects:Equivalent to: return replace(pos1, n1, str.data(), str.size());

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

Effects:Equivalent to:

return replace(pos1, n1, basic_string_view<charT, traits>(str).substr(pos2, n2));

template<class T> constexpr basic_string& replace(size_type pos1, size_type n1, const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return replace(pos1, n1, sv.data(), sv.size());

template<class T> constexpr basic_string& replace(size_type pos1, size_type n1, const T& t, size_type pos2, size_type n2 = npos);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return replace(pos1, n1, sv.substr(pos2, n2));

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

Preconditions: [s, s + n2) is a valid range.

Throws:

• out_­of_­range if pos1 > size(),
• length_­error if the length of the resulting string would exceed max_­size() (see below), or
• any exceptions thrown by allocator_­traits<Allocator>​::​allocate.

Effects:Determines the effective length xlen of the string to be removed as the smaller of n1 and size() - pos1.

Ifsize() - xlen >= max_­size() - n2 throws length_­error.

Otherwise, the function replaces the characters in the range[begin() + pos1, begin() + pos1 + xlen)with a copy of the range [s, s + n2).

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

Effects:Equivalent to: return replace(pos, n, s, traits​::​length(s));

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

Throws:

• out_­of_­range if pos1 > size(),
• length_­error if the length of the resulting string would exceed max_­size() (see below), or
• any exceptions thrown by allocator_­traits<Allocator>​::​allocate.

Effects:Determines the effective length xlen of the string to be removed as the smaller of n1 and size() - pos1.

Ifsize() - xlen >= max_­size() - n2 throws length_­error.

Otherwise, the function replaces the characters in the range[begin() + pos1, begin() + pos1 + xlen)with n2 copies of c.

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

Effects:Equivalent to: return replace(i1, i2, basic_­string_­view<charT, traits>(str));

template<class T> constexpr basic_string& replace(const_iterator i1, const_iterator i2, const T& t);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

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

Effects:Equivalent to:

basic_string_view<charT, traits> sv = t; return replace(i1 - begin(), i2 - i1, sv.data(), sv.size());

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

Effects:Equivalent to: return replace(i1, i2, basic_­string_­view<charT, traits>(s, n));

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

Effects:Equivalent to: return replace(i1, i2, basic_­string_­view<charT, traits>(s));

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

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

Effects:Equivalent to: return replace(i1 - begin(), i2 - i1, n, c);

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

Effects:Equivalent to: return replace(i1, i2, basic_­string(j1, j2, get_­allocator()));

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

Effects:Equivalent to: return replace(i1, i2, il.begin(), il.size());

21.3.2.6.7 basic_­string​::​copy [string.copy]

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

Effects:Equivalent to:return basic_­string_­view<charT, traits>(*this).copy(s, n, pos);

[ Note

: This does not terminate s with a null object. — end note

]

21.3.2.6.8 basic_­string​::​swap [string.swap]

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

Preconditions: allocator_­traits<Allocator>​::​propagate_­on_­container_­swap​::​value is trueorget_­allocator() == s.get_­allocator().

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

Complexity:Constant time.

21.3.2.7 String operations [string.ops]

21.3.2.7.1 Accessors [string.accessors]

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

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

Complexity:Constant time.

Remarks:The program shall not modify any of the values stored in the character array; otherwise, the behavior is undefined.

constexpr charT* data() noexcept;

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

Complexity:Constant time.

Remarks:The program shall not modify the value stored at p + size()to any value other than charT(); otherwise, the behavior is undefined.

constexpr operator basic_string_view<charT, traits>() const noexcept;

Effects:Equivalent to:return basic_­string_­view<charT, traits>(data(), size());

constexpr allocator_type get_allocator() const noexcept;

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

21.3.2.7.2 Searching [string.find]

Let F be one offind, rfind, find_­first_­of, find_­last_­of,find_­first_­not_­of, and find_­last_­not_­of.

• Each member function of the form
  constexpr size_type F(const basic_string& str, size_type pos) const noexcept;
  has effects equivalent to:return F(basic_­string_­view<charT, traits>(str), pos);
• Each member function of the form
  constexpr size_type F(const charT* s, size_type pos) const;
  has effects equivalent to:return F(basic_­string_­view<charT, traits>(s), pos);
• Each member function of the form
  constexpr size_type F(const charT* s, size_type pos, size_type n) const;
  has effects equivalent to:return F(basic_­string_­view<charT, traits>(s, n), pos);
• Each member function of the form
  constexpr size_type F(charT c, size_type pos) const noexcept;
  has effects equivalent to:
  return F(basic_string_view<charT, traits>(addressof(c), 1), pos);

template<class T> constexpr size_type find(const T& t, size_type pos = 0) const noexcept(see below);template<class T> constexpr size_type rfind(const T& t, size_type pos = npos) const noexcept(see below);template<class T> constexpr size_type find_first_of(const T& t, size_type pos = 0) const noexcept(see below);template<class T> constexpr size_type find_last_of(const T& t, size_type pos = npos) const noexcept(see below);template<class T> constexpr size_type find_first_not_of(const T& t, size_type pos = 0) const noexcept(see below);template<class T> constexpr size_type find_last_not_of(const T& t, size_type pos = npos) const noexcept(see below);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Let G be the name of the function.

Equivalent to:

basic_string_view<charT, traits> s = *this, sv = t; return s.G(sv, pos);

Remarks:The expression inside noexcept is equivalent tois_­nothrow_­convertible_­v<const T&, basic_­string_­view<charT, traits>>.

21.3.2.7.3 basic_­string​::​substr [string.substr]

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

Throws: out_­of_­rangeifpos > size().

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

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

21.3.2.7.4 basic_­string​::​compare [string.compare]

template<class T> constexpr int compare(const T& t) const noexcept(see below);

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to: return basic_­string_­view<charT, traits>(*this).compare(t);

Remarks:The expression inside noexcept is equivalent tois_­nothrow_­convertible_­v<const T&, basic_­string_­view<charT, traits>>.

template<class T> constexpr int compare(size_type pos1, size_type n1, const T& t) const;

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

return basic_string_view<charT, traits>(*this).substr(pos1, n1).compare(t);

template<class T> constexpr int compare(size_type pos1, size_type n1, const T& t, size_type pos2, size_type n2 = npos) const;

Constraints:

• is_­convertible_­v<const T&, basic_­string_­view<charT, traits>> istrue and
• is_­convertible_­v<const T&, const charT*> isfalse.

Effects:Equivalent to:

basic_string_view<charT, traits> s = *this, sv = t; return s.substr(pos1, n1).compare(sv.substr(pos2, n2));

constexpr int compare(const basic_string& str) const noexcept;

Effects:Equivalent to:return compare(basic_­string_­view<charT, traits>(str));

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

Effects:Equivalent to:return compare(pos1, n1, basic_­string_­view<charT, traits>(str));

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

Effects:Equivalent to:

return compare(pos1, n1, basic_string_view<charT, traits>(str), pos2, n2);

constexpr int compare(const charT* s) const;

Effects:Equivalent to:return compare(basic_­string_­view<charT, traits>(s));

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

Effects:Equivalent to: return compare(pos, n1, basic_­string_­view<charT, traits>(s));

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

Effects:Equivalent to: return compare(pos, n1, basic_­string_­view<charT, traits>(s, n2));

21.3.2.7.5 basic_­string​::​starts_­with [string.starts.with]

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;

Effects:Equivalent to:

return basic_string_view<charT, traits>(data(), size()).starts_with(x);

21.3.2.7.6 basic_­string​::​ends_­with [string.ends.with]

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;

Effects:Equivalent to:

return basic_string_view<charT, traits>(data(), size()).ends_with(x);