[basic.string.general]

# 27 Strings library [[strings]](./#strings)

## 27.4 String classes [[string.classes]](string.classes#basic.string.general)

### 27.4.3 Class template basic_string [[basic.string]](basic.string#general)

#### 27.4.3.1 General [basic.string.general]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L1994)

The
class templatebasic_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[.](#1.sentence-1)

Such a sequence is also called a “string” if the type of the
char-like objects that it holds
is clear from context[.](#1.sentence-2)

In the rest of [[basic.string]](basic.string "27.4.3 Class template basic_­string"),
the type of the char-like objects held in a basic_string object
is designated by charT[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2008)

A specialization of basic_string is a contiguous container ([[container.reqmts]](container.reqmts "23.2.2.2 Container requirements"))[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2011)

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[.](#3.sentence-1)

[🔗](#lib:basic_string_)

namespace std {template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>class basic_string {public:// typesusing 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*; // see [[container.requirements]](container.requirements "23.2 Requirements")using const_iterator = *implementation-defined*; // see [[container.requirements]](container.requirements "23.2 Requirements")using reverse_iterator = std::reverse_iterator<iterator>; using const_reverse_iterator = std::reverse_iterator<const_iterator>; static constexpr size_type npos = size_type(-1); // [[string.cons]](string.cons "27.4.3.3 Constructors and assignment operators"), construct/copy/destroyconstexpr 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()); 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()); 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());
 basic_string(nullptr_t) = delete; 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()); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<charT> R>constexpr basic_string(from_range_t, R&& rg, 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);
 basic_string& operator=(nullptr_t) = delete; constexpr basic_string& operator=(charT c); constexpr basic_string& operator=(initializer_list<charT>); // [[string.iterators]](string.iterators "27.4.3.4 Iterator support"), iteratorsconstexpr 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; // [[string.capacity]](string.capacity "27.4.3.5 Capacity"), capacityconstexpr size_type size() const noexcept; constexpr size_type length() const noexcept; constexpr size_type max_size() const noexcept; constexpr void resize(size_type n, charT c); constexpr void resize(size_type n); template<class Operation> constexpr void resize_and_overwrite(size_type n, Operation op); constexpr size_type capacity() const noexcept; constexpr void reserve(size_type res_arg); constexpr void shrink_to_fit(); constexpr void clear() noexcept; constexpr bool empty() const noexcept; // [[string.access]](string.access "27.4.3.6 Element access"), element accessconstexpr 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(); // [[string.modifiers]](string.modifiers "27.4.3.7 Modifiers"), modifiersconstexpr 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); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<charT> R>constexpr basic_string& append_range(R&& rg); 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); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<charT> R>constexpr basic_string& assign_range(R&& rg); 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); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<charT> R>constexpr iterator insert_range(const_iterator p, R&& rg); 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); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<charT> R>constexpr basic_string& replace_with_range(const_iterator i1, const_iterator i2, R&& rg); constexpr basic_string& replace(const_iterator, const_iterator, initializer_list<charT>); constexpr size_type copy(charT* s, size_type n, size_type pos = 0) const; constexpr void swap(basic_string& str)noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value || allocator_traits<Allocator>::is_always_equal::value); // [[string.ops]](string.ops "27.4.3.8 String operations"), string operationsconstexpr 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 &; constexpr basic_string substr(size_type pos = 0, size_type n = npos) &&; constexpr basic_string_view<charT, traits> subview(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; constexpr bool contains(basic_string_view<charT, traits> x) const noexcept; constexpr bool contains(charT x) const noexcept; constexpr bool contains(const charT* x) const; }; template<class 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>; template<ranges::[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Allocator = allocator<ranges::range_value_t<R>>> basic_string(from_range_t, R&&, Allocator = Allocator())-> basic_string<ranges::range_value_t<R>, char_traits<ranges::range_value_t<R>>,
 Allocator>; template<class charT, class traits, class Allocator = allocator<charT>>explicit basic_string(basic_string_view<charT, traits>, const Allocator& = Allocator())-> basic_string<charT, traits, Allocator>; template<class charT, class traits, class Allocator = allocator<charT>> basic_string(basic_string_view<charT, traits>, typename *see below*::size_type, typename *see below*::size_type, const Allocator& = Allocator())-> basic_string<charT, traits, Allocator>;}

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2351)

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[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2357)

The types iterator and const_iterator meet
the constexpr iterator requirements ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General"))[.](#5.sentence-1)