[string.view] (original) (raw)

21.4.3.1 General [string.view.template.general]

namespace std { template<class charT, class traits = char_traits<charT>> class basic_string_view { public: using traits_type = traits;using value_type = charT;using pointer = value_type*;using const_pointer = const value_type*;using reference = value_type&;using const_reference = const value_type&;using const_iterator = implementation-defined; using iterator = const_iterator;229 using const_reverse_iterator = reverse_iterator<const_iterator>;using reverse_iterator = const_reverse_iterator;using size_type = size_t;using difference_type = ptrdiff_t;static constexpr size_type npos = size_type(-1);constexpr basic_string_view() noexcept;constexpr basic_string_view(const basic_string_view&) noexcept = default;constexpr basic_string_view& operator=(const basic_string_view&) noexcept = default;constexpr basic_string_view(const charT* str);constexpr basic_string_view(const charT* str, size_type len);template<class It, class End> constexpr basic_string_view(It begin, End end);constexpr const_iterator begin() const noexcept;constexpr const_iterator end() const noexcept;constexpr const_iterator cbegin() const noexcept;constexpr const_iterator cend() const noexcept;constexpr const_reverse_iterator rbegin() const noexcept;constexpr const_reverse_iterator rend() 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;[[nodiscard]] constexpr bool empty() const noexcept;constexpr const_reference operator[](size_type pos) const;constexpr const_reference at(size_type pos) const;constexpr const_reference front() const;constexpr const_reference back() const;constexpr const_pointer data() const noexcept;constexpr void remove_prefix(size_type n);constexpr void remove_suffix(size_type n);constexpr void swap(basic_string_view& s) noexcept;constexpr size_type copy(charT* s, size_type n, size_type pos = 0) const;constexpr basic_string_view substr(size_type pos = 0, size_type n = npos) const;constexpr int compare(basic_string_view s) const noexcept;constexpr int compare(size_type pos1, size_type n1, basic_string_view s) const;constexpr int compare(size_type pos1, size_type n1, basic_string_view s, size_type pos2, size_type n2) 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 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 x) const noexcept;constexpr bool ends_with(charT x) const noexcept;constexpr bool ends_with(const charT* x) const;constexpr size_type find(basic_string_view s, size_type pos = 0) const noexcept;constexpr size_type find(charT c, 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 rfind(basic_string_view s, size_type pos = npos) const noexcept;constexpr size_type rfind(charT c, 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 find_first_of(basic_string_view s, size_type pos = 0) const noexcept;constexpr size_type find_first_of(charT c, 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_last_of(basic_string_view s, size_type pos = npos) const noexcept;constexpr size_type find_last_of(charT c, 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_first_not_of(basic_string_view s, size_type pos = 0) const noexcept;constexpr size_type find_first_not_of(charT c, 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_last_not_of(basic_string_view s, size_type pos = npos) const noexcept;constexpr size_type find_last_not_of(charT c, 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;private: const_pointer data_; size_type size_; };template<class It, class End> basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;}

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

[Note 1:

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

— _end note_]

For a basic_string_view str, any operation that invalidates a pointer in the range [str.data(), str.data() + str.size()) invalidates pointers, iterators, and references returned from str's member functions.

The complexity of basic_string_view member functions is unless otherwise specified.

21.4.3.2 Construction and assignment [string.view.cons]

constexpr basic_string_view() noexcept;

Postconditions: size_ == 0 and data_ == nullptr.

constexpr basic_string_view(const charT* str);

Preconditions: [str, str + traits::length(str)) is a valid range.

Effects: Constructs a basic_string_view, initializing data_ with strand initializing size_ with traits::length(str).

constexpr basic_string_view(const charT* str, size_type len);

Preconditions: [str, str + len) is a valid range.

Effects: Constructs a basic_string_view, initializing data_ with strand initializing size_ with len.

template<class It, class End> constexpr basic_string_view(It begin, End end);

Constraints:

is_same_v<iter_value_t<It>, charT> is true.
is_convertible_v<End, size_type> is false.

Preconditions:

[begin, end) is a valid range.

Effects: Initializes data_ with to_address(begin) and initializes size_ with end - begin.

21.4.3.3 Iterator support [string.view.iterators]

using const_iterator = _implementation-defined_;

All requirements on container iterators ([container.requirements]) apply to basic_string_view::const_iterator as well.

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

Returns: An iterator such that

if !empty(), addressof(*begin()) == data_,
otherwise, an unspecified value such that [begin(), end()) is a valid range.

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

Returns: begin() + size().

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

Returns: const_reverse_iterator(end()).

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

Returns: const_reverse_iterator(begin()).

21.4.3.4 Capacity [string.view.capacity]

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

constexpr size_type max_size() const noexcept;

Returns: The largest possible number of char-like objects that can be referred to by a basic_string_view.

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

21.4.3.5 Element access [string.view.access]

constexpr const_reference operator[](size_type pos) const;

Preconditions: pos < size().

[Note 1:

Unlike basic_string::operator[],basic_string_view::operator[](size()) has undefined behavior instead of returning charT().

— _end note_]

constexpr const_reference at(size_type pos) const;

Throws: out_of_range if pos >= size().

constexpr const_reference front() const;

constexpr const_reference back() const;

Returns: data_[size() - 1].

constexpr const_pointer data() const noexcept;

[Note 2:

Unlike basic_string::data() and string-literals,data() can return a pointer to a buffer that is not null-terminated.

Therefore it is typically a mistake to pass data() to a function that takes just a const charT* and expects a null-terminated string.

— _end note_]

21.4.3.6 Modifiers [string.view.modifiers]

constexpr void remove_prefix(size_type n);

Preconditions: n <= size().

Effects: Equivalent to: data_ += n; size_ -= n;

constexpr void remove_suffix(size_type n);

Preconditions: n <= size().

Effects: Equivalent to: size_ -= n;

constexpr void swap(basic_string_view& s) noexcept;

Effects: Exchanges the values of *this and s.

21.4.3.7 String operations [string.view.ops]

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

Let rlen be the smaller of n and size() - pos.

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

Effects: Equivalent to traits::copy(s, data() + pos, rlen).

Throws: out_of_range if pos > size().

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

Let rlen be the smaller of n and size() - pos.

Effects: Determines rlen, the effective length of the string to reference.

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

Throws: out_of_range if pos > size().

constexpr int compare(basic_string_view str) const noexcept;

Let rlen be the smaller of size() and str.size().

Effects: Determines rlen, the effective length of the strings to compare.

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 70 .

Table 70: compare() results [tab:string.view.compare]

🔗	Condition	Return Value
🔗	size() < str.size()	< 0
🔗	size() == str.size()	0
🔗	size() > str.size()	> 0

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

Effects: Equivalent to: return substr(pos1, n1).compare(str);

constexpr int compare(size_type pos1, size_type n1, basic_string_view str, size_type pos2, size_type n2) const;

Effects: Equivalent to: return substr(pos1, n1).compare(str.substr(pos2, n2));

constexpr int compare(const charT* s) const;

Effects: Equivalent to: return compare(basic_string_view(s));

constexpr int compare(size_type pos1, size_type n1, const charT* s) const;

Effects: Equivalent to: return substr(pos1, n1).compare(basic_string_view(s));

constexpr int compare(size_type pos1, size_type n1, const charT* s, size_type n2) const;

Effects: Equivalent to: return substr(pos1, n1).compare(basic_string_view(s, n2));

constexpr bool starts_with(basic_string_view x) const noexcept;

Effects: Equivalent to: return substr(0, x.size()) == x;

constexpr bool starts_with(charT x) const noexcept;

Effects: Equivalent to: return !empty() && traits::eq(front(), x);

constexpr bool starts_with(const charT* x) const;

Effects: Equivalent to: return starts_with(basic_string_view(x));

constexpr bool ends_with(basic_string_view x) const noexcept;

Effects: Equivalent to:return size() >= x.size() && compare(size() - x.size(), npos, x) == 0;

constexpr bool ends_with(charT x) const noexcept;

Effects: Equivalent to: return !empty() && traits::eq(back(), x);

constexpr bool ends_with(const charT* x) const;

Effects: Equivalent to: return ends_with(basic_string_view(x));

21.4.3.8 Searching [string.view.find]

Member functions in this subclause have complexity at worst, although implementations should do better.

Let F be one offind,rfind,find_first_of,find_last_of,find_first_not_of, andfind_last_not_of.

Each member function of the formconstexpr return-type F(const charT* s, size_type pos) const;has effects equivalent to: return F(basic_string_view(s), pos);
Each member function of the formconstexpr return-type F(const charT* s, size_type pos, size_type n) const;has effects equivalent to: return F(basic_string_view(s, n), pos);
Each member function of the formconstexpr return-type F(charT c, size_type pos) const noexcept;has effects equivalent to: return F(basic_string_view(addressof(c), 1), pos);

constexpr size_type find(basic_string_view str, size_type pos = 0) const noexcept;

Let xpos be the lowest position, if possible, such that the following conditions hold:

pos <= xpos
xpos + str.size() <= size()
traits::eq(at(xpos + I), str.at(I)) for all elements I of the string referenced by str.

Effects: Determines xpos.