标准库头文件 <string_view>

namespace std {
 
// 类模板 basic_string_view
template<class charT, class traits = char_traits<charT>>
class basic_string_view;
 
// 非成员比较函数
template<class charT, class traits>
constexpr bool operator==(basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
template<class charT, class traits>
constexpr bool operator!=(basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
template<class charT, class traits>
constexpr bool operator< (basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
template<class charT, class traits>
constexpr bool operator> (basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
template<class charT, class traits>
constexpr bool operator<=(basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
template<class charT, class traits>
constexpr bool operator>=(basic_string_view<charT, traits> x,
                          basic_string_view<charT, traits> y) noexcept;
/* 充足的比较函数的额外重载 */
 
// 插入符与提取符
template<class charT, class traits>
basic_ostream<charT, traits>& 
operator<<(basic_ostream<charT, traits>& os, basic_string_view<charT, traits> str);
 
// basic_string_view typedef 名
using string_view    = basic_string_view<char>;
using u8string_view  = basic_string_view<char8_t>;
using u16string_view = basic_string_view<char16_t>;
using u32string_view = basic_string_view<char32_t>;
using wstring_view   = basic_string_view<wchar_t>;
 
// 散列支持
template<class T> struct hash;
template<> struct hash<string_view>;
template<> struct hash<u8string_view>;
template<> struct hash<u16string_view>;
template<> struct hash<u32string_view>;
template<> struct hash<wstring_view>;
 
inline namespace literals {
inline namespace string_view_literals {
// basic_string_view 字面量的后缀
constexpr string_view operator "" sv(const char* str, size_t len) noexcept;
constexpr u8string_view operator "" sv(const char16_t* str, size_t len) noexcept;
constexpr u16string_view operator "" sv(const char16_t* str, size_t len) noexcept;
constexpr u32string_view operator "" sv(const char32_t* str, size_t len) noexcept;
constexpr wstring_view operator "" sv(const wchar_t* str, size_t len) noexcept;
}
}
} // namespace std

template<class charT, class traits = char_traits<charT>>
class basic_string_view {
public:
// 类型
typedef traits traits_type;
typedef charT value_type;
typedef charT* pointer;
typedef const charT* const_pointer;
typedef charT& reference;
typedef const charT& const_reference;
typedef /* 由实现定义 */ const_iterator;
typedef const_iterator iterator;
typedef reverse_iterator<const_iterator> const_reverse_iterator;
typedef const_reverse_iterator reverse_iterator;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
static constexpr size_type npos = size_type(-1);
 
// 构造与赋值
constexpr basic_string_view() noexcept;
constexpr basic_string_view(const basic_string_view&) noexcept = default;
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);
 
// 迭代器支持
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;
 
// 容量
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;
 
// 元素访问
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;
 
// 修改器
constexpr void remove_prefix(size_type n);
constexpr void remove_suffix(size_type n);
constexpr void swap(basic_string_view& s) noexcept;
 
// 字符串操作
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_; // 仅用于阐释
size_type size_; // 仅用于阐释
};
 
}