标准库标头 <string_view>

 

C++

编译器支持

自立实现与有宿主实现

语言

标准库

标准库标头

具名要求

功能特性测试宏 (C++20)

语言支持库

概念库 (C++20)

元编程库 (C++11)

诊断库

通用工具库

字符串库

容器库

迭代器库

范围库 (C++20)

算法库

数值库

本地化库

输入/输出库

文件系统库 (C++17)

正则表达式库 (C++11)

并发支持库 (C++11)

技术规范

符号索引

外部库

 

标准库标头

注：修订记号中的反斜杠 '/' 意味着此标头被弃用和/或被移除。

语言支持
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
概念
<concepts> (C++20)
诊断
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
内存管理
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
元编程
<type_traits> (C++11)	<ratio> (C++11)
通用工具
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
字符串
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
容器
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23)
迭代器
<iterator>
范围
<ranges> (C++20)	<generator> (C++23)
算法
<algorithm>	<execution>
数值
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath>	<numbers> (C++20)
日期时间
<chrono> (C++11)	<ctime>
本地化
<locale>	<clocale>	<codecvt> (C++11/17)
输入/输出
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98/)
正则表达式
<regex>
并发支持
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11)
C 兼容
<cstdbool> (C++11/17/20)   <ccomplex> (C++11/17/20)	<ctgmath> (C++11/17/20)	<cstdalign> (C++11/17/20)	<ciso646> (C++20 前)

 

此头文件是字符串库的一部分。

包含
<compare> (C++20)	三路比较运算符支持
类
basic_string_view (C++17)	只读的字符串视图 (类模板)
std::string_view (C++17)	std::basic_string_view<char>
std::u8string_view (C++20)	std::basic_string_view<char8_t>
std::u16string_view (C++17)	std::basic_string_view<char16_t>
std::u32string_view (C++17)	std::basic_string_view<char32_t>
std::wstring_view (C++17)	std::basic_string_view<wchar_t>
std::hash<std::string_view>std::hash<std::wstring_view>std::hash<std::u8string_view>std::hash<std::u16string_view>std::hash<std::u32string_view> (C++17)(C++17)(C++20)(C++17)(C++17)	string_view 的散列支持 (类模板特化)
前置声明
在标头 <functional> 定义
hash (C++11)	散列函数对象 (类模板)
函数
operator==operator!=operator<operator>operator<=operator>=operator<=> (C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20)	以字典序比较两个字符串视图 (函数模板)
operator<<	进行字符串视图的流输出 (函数模板)
swap	交换两个对象的值 (函数模板)
范围访问
begincbegin (C++11)(C++14)	返回指向容器或数组起始的迭代器 (函数模板)
endcend (C++11)(C++14)	返回指向容器或数组结尾的迭代器 (函数模板)
rbegincrbegin (C++14)	返回指向一个容器或数组的逆向迭代器 (函数模板)
rendcrend (C++14)	返回容器或数组的逆向尾迭代器 (函数模板)
sizessize (C++17)(C++20)	返回容器或数组的大小 (函数模板)
empty (C++17)	检查容器是否为空 (函数模板)
data (C++17)	获得指向底层数组的指针 (函数模板)
字面量
在内联命名空间 std::literals::string_view_literals 定义
operator""sv (C++17)	创建一个字符数组字面量的字符串视图 (函数)

概要

#include <compare>
 
namespace std {
  // 类模板 basic_­string_­view
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_string_view;
 
  template<class CharT, class Traits>
    inline constexpr bool ranges::enable_view<basic_string_view<CharT, Traits>> = true;
  template<class CharT, class Traits>
    inline constexpr bool ranges::enable_borrowed_range<basic_string_view<CharT, Traits>> =
      true;
 
  // 非成员函数
  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 /* 见描述 */
      operator<=>(basic_string_view<CharT, Traits> x,
                  basic_string_view<CharT, Traits> y) noexcept;
 
  // 充足的比较函数额外重载
 
  // 插入器与提取器
  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 char8_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;
  }
  }
}

类模板 std::basic_string_view

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_string_view {
  public:
    // 类型
    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         = /* 由实现定义 */
    using iterator               = const_iterator;
    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);
 
    // 构造与赋值
    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(nullptr_t) = delete;
    constexpr basic_string_view(const CharT* str, size_type len);
    template<class It, class End>
      constexpr basic_string_view(It begin, End end);
    template<class R>
      constexpr explicit basic_string_view(R&& r);
 
    // 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 bool contains(basic_string_view x) const noexcept;
    constexpr bool contains(CharT x) const noexcept;
    constexpr bool contains(const CharT* x) const;
 
    // 搜索
    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
  };
 
  // 推导指引
  template<class It, class End>
    basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;
 
  template<class R>
    basic_string_view(R&&) -> basic_string_view<ranges::range_value_t<R>>;
}