23 Strings library [strings]

23.4 String classes [string.classes]

23.4.3 Class template basic_string [basic.string]

23.4.3.3 Constructors and assignment operators [string.cons]

constexpr explicit basic_string(const Allocator& a) noexcept;

Postconditions: size() is equal to 0.

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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.

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

Let

(4.1)
s be the value of str prior to this call and
(4.2)
rlen be pos + min(n, s.size() - pos) for the overloads with parameter n, and s.size() otherwise.

Effects: Constructs an object whose initial value is the range [s.data() + pos, s.data() + rlen).

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

Remarks: For the overloads with a basic_string&& parameter, str is left in a valid but unspecified state.

Recommended practice: For the overloads with a basic_string&& parameter, implementations should avoid allocation if s.get_allocator() == a is true.

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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);

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

Constraints:

(11.1)
is_convertible_v<const T&, basic_string_view<charT, traits>> is true and
(11.2)
is_convertible_v<const T&, const charT*> is false.

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

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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, and traits::compare(data(), s, n) is equal to 0.

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

Constraints: Allocator is a type

that qualifies as an allocator ([container.reqmts]).

[Note 1:

This affects class template argument deduction.

— end note]

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

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

Constraints: Allocator is a type that qualifies as an allocator ([container.reqmts]).

[Note 2:

This affects class template argument deduction.

— end note]

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

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

Constraints: InputIterator is a type that qualifies as an input iterator ([container.reqmts]).

Effects: Constructs a string from the values in the range [begin, end), as specified in [sequence.reqmts].

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template<container-compatible-range<charT> R>
  constexpr basic_string(from_range_t, R&& rg, const Allocator& = Allocator());

Effects: Constructs a string from the values in the range rg, as specified in [sequence.reqmts].

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

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

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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().

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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.reqmts]).

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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>;

Constraints: Allocator is a type that qualifies as an allocator ([container.reqmts]).

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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.

Returns: *this.

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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 ([sequence.reqmts]), except that iterators, pointers and references may be invalidated.

Returns: *this.

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

Constraints:

(32.1)
is_convertible_v<const T&, basic_string_view<charT, traits>> is true and
(32.2)
is_convertible_v<const T&, const charT*> is false.

Effects: Equivalent to: basic_string_view<charT, traits> sv = t; return assign(sv);

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

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

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constexpr basic_string& operator=(charT c);

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

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

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