标准库标头 <regex>

 

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标准库头

语言支持 <cfloat> <climits> <compare> (C++20) <contracts> (C++26) <coroutine> (C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint> (C++11) <cstdlib> <exception> <initializer_list> (C++11)    <limits> <new> <source_location> (C++20) <stdfloat> (C++23) <typeinfo> <version> (C++20) 概念 <concepts> (C++20) 诊断 <cassert> <cerrno> <debugging> (C++26) <stacktrace> (C++23) <stdexcept> <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 <any> (C++17) <bitset> <bit> (C++20) <charconv> (C++17) <expected> (C++23) <format> (C++20) <functional> <optional> (C++17) <stdbit.h> (C++26) <tuple> (C++11) <typeindex> (C++11) <utility> <variant> (C++17) 容器 <array> (C++11) <deque> <flat_map> (C++23) <flat_set> (C++23) <forward_list> (C++11) <hive> (C++26) <inplace_vector> (C++26)    <list> <map> <mdspan> (C++23) <queue> <set> <span> (C++20) <stack> <unordered_map> (C++11) <unordered_set> (C++11) <vector> 迭代器 <iterator> 范围 <generator> (C++23) <ranges> (C++20)

算法 <algorithm> <numeric> 字符串 <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> 文本处理 <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)    cpp/header#数值库数值 <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <simd> (C++26) <stdckdint.h> (C++26) <valarray> 时间 <chrono> (C++11) <ctime> C 兼容性 <ccomplex> (C++11/17/20*) <ciso646> (C++20 前) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

输入/输出 <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) 并发支持 <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) 执行支持 <execution> (C++17)

 

此标头是文本处理库的一部分。

包含
<compare> (C++20)	三路比较运算符支持
<initializer_list> (C++11)	std::initializer_list 类模板
类
basic_regex (C++11)	正则表达式对象 (类模板)
std::regex	std::basic_regex<char> (typedef)
std::wregex	std::basic_regex<wchar_t> (typedef)
sub_match (C++11)	标识子表达式所匹配的字符序列 (类模板)
std::csub_match	std::sub_match<const char*> (typedef)
std::wcsub_match	std::sub_match<const wchar_t*> (typedef)
std::ssub_match	std::sub_match<std::string::const_iterator> (typedef)
std::wssub_match	std::sub_match<std::wstring::const_iterator> (typedef)
match_results (C++11)	标识一个正则表达式匹配，包含所有子表达式匹配 (类模板)
std::cmatch	std::match_results<const char*> (typedef)
std::wcmatch	std::match_results<const wchar_t*> (typedef)
std::smatch	std::match_results<std::string::const_iterator> (typedef)
std::wsmatch	std::match_results<std::wstring::const_iterator> (typedef)
regex_iterator (C++11)	迭代一个字符序列中的所有正则表达式匹配 (类模板)
std::cregex_iterator	std::regex_iterator<const char*> (typedef)
std::wcregex_iterator	std::regex_iterator<const wchar_t*> (typedef)
std::sregex_iterator	std::regex_iterator<std::string::const_iterator> (typedef)
std::wsregex_iterator	std::regex_iterator<std::wstring::const_iterator> (typedef)
regex_token_iterator (C++11)	迭代给定字符串中的所有正则表达式匹配中的指定子表达式，或迭代未匹配的子字符串 (类模板)
std::cregex_token_iterator	std::regex_token_iterator<const char*> (typedef)
std::wcregex_token_iterator	std::regex_token_iterator<const wchar_t*> (typedef)
std::sregex_token_iterator	std::regex_token_iterator<std::string::const_iterator> (typedef)
std::wsregex_token_iterator	std::regex_token_iterator<std::wstring::const_iterator> (typedef)
regex_error (C++11)	报告正则表达式库生成的错误 (类)
regex_traits (C++11)	提供正则表达式库所需的关于字符类型的元信息 (类模板)
regex 常量类型
在命名空间 std::regex_constants 定义
syntax_option_type (C++11)	控制正则表达式行为的通用选项 (typedef)
match_flag_type (C++11)	特定于匹配的选项 (typedef)
error_type (C++11)	描述不同类型的匹配错误 (typedef)
函数
算法
regex_match (C++11)	尝试匹配一个正则表达式到整个字符序列 (函数模板)
regex_search (C++11)	尝试匹配一个正则表达式到字符序列的任何部分 (函数模板)
regex_replace (C++11)	以格式化的替换文本来替换正则表达式匹配的出现位置 (函数模板)
非成员操作
std::swap(std::basic_regex) (C++11)	特化 std::swap 算法 (函数模板)
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 移除)(C++20 移除)(C++20 移除)(C++20 移除)(C++20 移除)(C++20)	比较一个 sub_match 与另一 sub_match 、字符串或字符 (函数模板)
operator<<	输出匹配的字符子序列 (函数模板)
operator==operator!= (C++20 移除)	以字典序比较两个匹配结果的值 (函数模板)
std::swap(std::match_results) (C++11)	特化 std::swap 算法 (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)

概要

#include <compare>
#include <initializer_list>

namespace std {
  // regex 常量
  namespace regex_constants {
    using syntax_option_type = /*T1*/;
    using match_flag_type = /*T2*/;
    using error_type = /*T3*/;
  }

  // 类 regex_­error
  class regex_error;

  // 类模板 regex_traits
  template<class CharT> struct regex_traits;

  // 类模板 basic_­regex
  template<class CharT, class Traits = regex_traits<CharT>> class basic_regex;

  using regex  = basic_regex<char>;
  using wregex = basic_regex<wchar_t>;

  // basic_­regex 交换
  template<class CharT, class Traits>
    void swap(basic_regex<CharT, Traits>& e1, basic_regex<CharT, Traits>& e2);

  // 类模板 sub_­match
  template<class BiIt>
    class sub_match;

  using csub_match  = sub_match<const char*>;
  using wcsub_match = sub_match<const wchar_t*>;
  using ssub_match  = sub_match<string::const_iterator>;
  using wssub_match = sub_match<wstring::const_iterator>;

  // sub_­match 非成员运算符
  template<class BiIt>
    bool operator==(const sub_match<BiIt>& lhs, const sub_match<BiIt>& rhs);
  template<class BiIt>
    auto operator<=>(const sub_match<BiIt>& lhs, const sub_match<BiIt>& rhs);

  template<class BiIt, class ST, class SA>
    bool operator==(
      const sub_match<BiIt>& lhs,
      const basic_string<typename iterator_traits<BiIt>::value_type, ST, SA>& rhs);
  template<class BiIt, class ST, class SA>
    auto operator<=>(
      const sub_match<BiIt>& lhs,
      const basic_string<typename iterator_traits<BiIt>::value_type, ST, SA>& rhs);

  template<class BiIt>
    bool operator==(const sub_match<BiIt>& lhs,
                    const typename iterator_traits<BiIt>::value_type* rhs);
  template<class BiIt>
    auto operator<=>(const sub_match<BiIt>& lhs,
                     const typename iterator_traits<BiIt>::value_type* rhs);

  template<class BiIt>
    bool operator==(const sub_match<BiIt>& lhs,
                    const typename iterator_traits<BiIt>::value_type& rhs);
  template<class BiIt>
    auto operator<=>(const sub_match<BiIt>& lhs,
                     const typename iterator_traits<BiIt>::value_type& rhs);

  template<class CharT, class ST, class BiIt>
    basic_ostream<CharT, ST>&
      operator<<(basic_ostream<CharT, ST>& os, const sub_match<BiIt>& m);

  // 类模板 match_­results
  template<class BiIt,
           class Allocator = allocator<sub_match<BiIt>>>
    class match_results;

  using cmatch  = match_results<const char*>;
  using wcmatch = match_results<const wchar_t*>;
  using smatch  = match_results<string::const_iterator>;
  using wsmatch = match_results<wstring::const_iterator>;

  // match_­results 比较
  template<class BiIt, class Allocator>
    bool operator==(const match_results<BiIt, Allocator>& m1,
                    const match_results<BiIt, Allocator>& m2);

  // match_­results 交换
  template<class BiIt, class Allocator>
    void swap(match_results<BiIt, Allocator>& m1, match_results<BiIt, Allocator>& m2);

  // 函数模板 regex_­match
  template<class BiIt, class Allocator, class CharT, class Traits>
    bool regex_match(BiIt first, BiIt last,
                     match_results<BiIt, Allocator>& m,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);
  template<class BiIt, class CharT, class Traits>
    bool regex_match(BiIt first, BiIt last,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);
  template<class CharT, class Allocator, class Traits>
    bool regex_match(const CharT* str, match_results<const CharT*, Allocator>& m,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);
  template<class ST, class SA, class Allocator, class CharT, class Traits>
    bool regex_match(const basic_string<CharT, ST, SA>& s,
                     match_results<typename basic_string<CharT, ST, SA>::const_iterator,
                                   Allocator>& m,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);
  template<class ST, class SA, class Allocator, class CharT, class Traits>
    bool regex_match(const basic_string<CharT, ST, SA>&&,
                     match_results<typename basic_string<CharT, ST, SA>::const_iterator,
                                   Allocator>&,
                     const basic_regex<CharT, Traits>&,
                     regex_constants::match_flag_type =
                       regex_constants::match_default) = delete;
  template<class CharT, class Traits>
    bool regex_match(const CharT* str,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);
  template<class ST, class SA, class CharT, class Traits>
    bool regex_match(const basic_string<CharT, ST, SA>& s,
                     const basic_regex<CharT, Traits>& e,
                     regex_constants::match_flag_type flags =
                       regex_constants::match_default);

  // 函数模板 regex_­search
  template<class BiIt, class Allocator, class CharT, class Traits>
    bool regex_search(BiIt first, BiIt last,
                      match_results<BiIt, Allocator>& m,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class BiIt, class CharT, class Traits>
    bool regex_search(BiItfirst, BiIt last,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class CharT, class Allocator, class Traits>
    bool regex_search(const CharT* str,
                      match_results<const CharT*, Allocator>& m,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class CharT, class Traits>
    bool regex_search(const CharT* str,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class ST, class SA, class CharT, class Traits>
    bool regex_search(const basic_string<CharT, ST, SA>& s,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class ST, class SA, class Allocator, class CharT, class Traits>
    bool regex_search(const basic_string<CharT, ST, SA>& s,
                      match_results<typename basic_string<CharT, ST, SA>::const_iterator,
                                    Allocator>& m,
                      const basic_regex<CharT, Traits>& e,
                      regex_constants::match_flag_type flags =
                        regex_constants::match_default);
  template<class ST, class SA, class Allocator, class CharT, class Traits>
    bool regex_search(const basic_string<CharT, ST, SA>&&,
                      match_results<typename basic_string<CharT, ST, SA>::const_iterator,
                                    Allocator>&,
                      const basic_regex<CharT, Traits>&,
                      regex_constants::match_flag_type
                        = regex_constants::match_default) = delete;

  // 函数模板 regex_­replace
  template<class OutputIt, class BiIt,
            class Traits, class CharT, class ST, class SA>
    OutputIt
      regex_replace(OutputIt out,
                    BiIt first, BiIt last,
                    const basic_regex<CharT, Traits>& e,
                    const basic_string<CharT, ST, SA>& fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);
  template<class OutputIt, class BiIt, class Traits, class CharT>
    OutputIt
      regex_replace(OutputIt out,
                    BiIt first, BiIt last,
                    const basic_regex<CharT, Traits>& e,
                    const CharT* fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);
  template<class Traits, class CharT, class ST, class SA, class FST, class FSA>
    basic_string<CharT, ST, SA>
      regex_replace(const basic_string<CharT, ST, SA>& s,
                    const basic_regex<CharT, Traits>& e,
                    const basic_string<CharT, FST, FSA>& fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);
  template<class Traits, class CharT, class ST, class SA>
    basic_string<CharT, ST, SA>
      regex_replace(const basic_string<CharT, ST, SA>& s,
                    const basic_regex<CharT, Traits>& e,
                    const CharT* fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);
  template<class Traits, class CharT, class ST, class SA>
    basic_string<CharT>
      regex_replace(const CharT* s,
                    const basic_regex<CharT, Traits>& e,
                    const basic_string<CharT, ST, SA>& fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);
  template<class Traits, class CharT>
    basic_string<CharT>
      regex_replace(const CharT* s,
                    const basic_regex<CharT, Traits>& e,
                    const CharT* fmt,
                    regex_constants::match_flag_type flags =
                      regex_constants::match_default);

  // 类模板 regex_­iterator
  template<class BiIt,
            class CharT = typename iterator_traits<BiIt>::value_type,
            class Traits = regex_traits<CharT>>
    class regex_iterator;

  using cregex_iterator  = regex_iterator<const char*>;
  using wcregex_iterator = regex_iterator<const wchar_t*>;
  using sregex_iterator  = regex_iterator<string::const_iterator>;
  using wsregex_iterator = regex_iterator<wstring::const_iterator>;

  // 类模板 regex_­token_­iterator
  template<class BiIt,
            class CharT = typename iterator_traits<BiIt>::value_type,
            class Traits = regex_traits<CharT>>
    class regex_token_iterator;

  using cregex_token_iterator  = regex_token_iterator<const char*>;
  using wcregex_token_iterator = regex_token_iterator<const wchar_t*>;
  using sregex_token_iterator  = regex_token_iterator<string::const_iterator>;
  using wsregex_token_iterator = regex_token_iterator<wstring::const_iterator>;

  namespace pmr {
    template<class BiIt>
      using match_results =
        std::match_results<BiIt, polymorphic_allocator<sub_match<BiIt>>>;

    using cmatch  = match_results<const char*>;
    using wcmatch = match_results<const wchar_t*>;
    using smatch  = match_results<string::const_iterator>;
    using wsmatch = match_results<wstring::const_iterator>;
  }
}

位掩码类型 std::regex_constants::syntax_option_type

namespace std::regex_constants {
  using syntax_option_type = /*T1*/;
  inline constexpr syntax_option_type icase = /* 未指明 */;
  inline constexpr syntax_option_type nosubs = /* 未指明 */;
  inline constexpr syntax_option_type optimize = /* 未指明 */;
  inline constexpr syntax_option_type collate = /* 未指明 */;
  inline constexpr syntax_option_type ECMAScript = /* 未指明 */;
  inline constexpr syntax_option_type basic = /* 未指明 */;
  inline constexpr syntax_option_type extended = /* 未指明 */;
  inline constexpr syntax_option_type awk = /* 未指明 */;
  inline constexpr syntax_option_type grep = /* 未指明 */;
  inline constexpr syntax_option_type egrep = /* 未指明 */;
  inline constexpr syntax_option_type multiline = /* 未指明 */;
}

位掩码类型 std::regex_constants::match_flag_type

namespace std::regex_constants {
  using match_flag_type = /*T2*/;
  inline constexpr match_flag_type match_­default = {};
  inline constexpr match_flag_type match_­not_­bol = /* 未指明 */;
  inline constexpr match_flag_type match_­not_­eol = /* 未指明 */;
  inline constexpr match_flag_type match_­not_­bow = /* 未指明 */;
  inline constexpr match_flag_type match_­not_­eow = /* 未指明 */;
  inline constexpr match_flag_type match_­any = /* 未指明 */;
  inline constexpr match_flag_type match_­not_­null = /* 未指明 */;
  inline constexpr match_flag_type match_­continuous = /* 未指明 */;
  inline constexpr match_flag_type match_­prev_­avail = /* 未指明 */;
  inline constexpr match_flag_type format_­default = {};
  inline constexpr match_flag_type format_­sed = /* 未指明 */;
  inline constexpr match_flag_type format_­no_­copy = /* 未指明 */;
  inline constexpr match_flag_type format_­first_­only = /* 未指明 */;
}

被枚举类型 std::regex_constants::error_type

namespace std::regex_constants {
  using error_type = /*T3*/;
  inline constexpr error_type error_collate = /* 未指明 */;
  inline constexpr error_type error_ctype = /* 未指明 */;
  inline constexpr error_type error_escape = /* 未指明 */;
  inline constexpr error_type error_backref = /* 未指明 */;
  inline constexpr error_type error_brack = /* 未指明 */;
  inline constexpr error_type error_paren = /* 未指明 */;
  inline constexpr error_type error_brace = /* 未指明 */;
  inline constexpr error_type error_badbrace = /* 未指明 */;
  inline constexpr error_type error_range = /* 未指明 */;
  inline constexpr error_type error_space = /* 未指明 */;
  inline constexpr error_type error_badrepeat = /* 未指明 */;
  inline constexpr error_type error_complexity = /* 未指明 */;
  inline constexpr error_type error_stack = /* 未指明 */;
}

类 std::regex_error

namespace std {
  class regex_error : public runtime_error {
  public:
    explicit regex_error(regex_constants::error_type ecode);
    regex_constants::error_type code() const;
  };
}

类模板 std::regex_traits

namespace std {
  template<class CharT>
    struct regex_traits {
      using char_type       = CharT;
      using string_type     = basic_string<char_type>;
      using locale_type     = locale;
      using char_class_type = /* 位掩码类型 */;

      regex_traits();
      static size_t length(const char_type* p);
      CharT translate(CharT c) const;
      CharT translate_nocase(CharT c) const;
      template<class ForwardIt>
        string_type transform(ForwardIt first, ForwardIt last) const;
      template<class ForwardIt>
        string_type transform_primary(ForwardIt first, ForwardIt last) const;
      template<class ForwardIt>
        string_type lookup_collatename(ForwardIt first, ForwardIt last) const;
      template<class ForwardIt>
        char_class_type lookup_classname(ForwardIt first, ForwardIt last,
                                         bool icase = false) const;
      bool isctype(CharT c, char_class_type f) const;
      int value(CharT ch, int radix) const;
      locale_type imbue(locale_type l);
      locale_type getloc() const;
    };
}

类模板 std::basic_regex

namespace std {
  template<class CharT, class Traits = regex_traits<CharT>>
    class basic_regex {
    public:
      // 类型
      using value_type  =          CharT;
      using Traits_type =          Traits;
      using string_type = typename Traits::string_type;
      using flag_type   =          regex_constants::syntax_option_type;
      using locale_type = typename Traits::locale_type;

      // 常量
      static constexpr flag_type icase = regex_constants::icase;
      static constexpr flag_type nosubs = regex_constants::nosubs;
      static constexpr flag_type optimize = regex_constants::optimize;
      static constexpr flag_type collate = regex_constants::collate;
      static constexpr flag_type ECMAScript = regex_constants::ECMAScript;
      static constexpr flag_type basic = regex_constants::basic;
      static constexpr flag_type extended = regex_constants::extended;
      static constexpr flag_type awk = regex_constants::awk;
      static constexpr flag_type grep = regex_constants::grep;
      static constexpr flag_type egrep = regex_constants::egrep;
      static constexpr flag_type multiline = regex_constants::multiline;

      // 构造/复制/销毁
      basic_regex();
      explicit basic_regex(const CharT* p, flag_type f = regex_constants::ECMAScript);
      basic_regex(const CharT* p, size_t len, flag_type f = regex_constants::ECMAScript);
      basic_regex(const basic_regex&);
      basic_regex(basic_regex&&) noexcept;
      template<class ST, class SA>
        explicit basic_regex(const basic_string<CharT, ST, SA>& s,
                             flag_type f = regex_constants::ECMAScript);
      template<class ForwardIt>
        basic_regex(ForwardIt first, ForwardIt last,
                    flag_type f = regex_constants::ECMAScript);
      basic_regex(initializer_list<CharT> il, flag_type f = regex_constants::ECMAScript);

      ~basic_regex();

      // 赋值
      basic_regex& operator=(const basic_regex& e);
      basic_regex& operator=(basic_regex&& e) noexcept;
      basic_regex& operator=(const CharT* p);
      basic_regex& operator=(initializer_list<CharT> il);
      template<class ST, class SA>
        basic_regex& operator=(const basic_string<CharT, ST, SA>& s);

      basic_regex& assign(const basic_regex& e);
      basic_regex& assign(basic_regex&& e) noexcept;
      basic_regex& assign(const CharT* p, flag_type f = regex_constants::ECMAScript);
      basic_regex& assign(const CharT* p, size_t len,
                          flag_type f = regex_constants::ECMAScript);
      template<class ST, class SA>
        basic_regex& assign(const basic_string<CharT, ST, SA>& s,
                            flag_type f = regex_constants::ECMAScript);
      template<class InputIt>
        basic_regex& assign(InputIt first, InputIt last,
                            flag_type f = regex_constants::ECMAScript);
      basic_regex& assign(initializer_list<CharT>,
                          flag_type f = regex_constants::ECMAScript);

      // const 操作
      unsigned mark_count() const;
      flag_type flags() const;

      // 本地环境
      locale_type imbue(locale_type loc);
      locale_type getloc() const;

      // 交换
      void swap(basic_regex&);
    };

  template<class ForwardIt>
    basic_regex(ForwardIt, ForwardIt,
                regex_constants::syntax_option_type = regex_constants::ECMAScript)
      -> basic_regex<typename iterator_traits<ForwardIt>::value_type>;
}

类模板 std::sub_match

namespace std {
  template<class BiIt>
    class sub_match : public pair<BiIt, BiIt> {
    public:
      using value_type      = typename iterator_traits<BiIt>::value_type;
      using difference_type = typename iterator_traits<BiIt>::difference_type;
      using iterator        = BiIt;
      using string_type     = basic_string<value_type>;

      bool matched;

      constexpr sub_match();

      difference_type length() const;
      operator string_type() const;
      string_type str() const;

      int compare(const sub_match& s) const;
      int compare(const string_type& s) const;
      int compare(const value_type* s) const;

      void swap(sub_match& s) noexcept(/* 见描述 */);
    };
}

类模板 std::match_results

namespace std {
  template<class BiIt,
           class Allocator = allocator<sub_match<BiIt>>>
    class match_results {
    public:
      using value_type      = sub_match<BiIt>;
      using const_reference = const value_type&;
      using reference       = value_type&;
      using const_iterator  = /* 由实现定义 */;
      using iterator        = const_iterator;
      using difference_type = typename iterator_traits<BiIt>::difference_type;
      using size_type       = typename allocator_traits<Allocator>::size_type;
      using allocator_type  = Allocator;
      using char_type       = typename iterator_traits<BiIt>::value_type;
      using string_type     = basic_string<char_type>;

      // 构造/复制/销毁
      match_results() : match_results(Allocator()) {}
      explicit match_results(const Allocator& a);
      match_results(const match_results& m);
      match_results(const match_results& m, const Allocator& a);
      match_results(match_results&& m) noexcept;
      match_results(match_results&& m, const Allocator& a);
      match_results& operator=(const match_results& m);
      match_results& operator=(match_results&& m);
      ~match_results();

      // 状态
      bool ready() const;

      // 大小
      size_type size() const;
      size_type max_size() const;
      bool empty() const;

      // 元素访问
      difference_type length(size_type sub = 0) const;
      difference_type position(size_type sub = 0) const;
      string_type str(size_type sub = 0) const;
      const_reference operator[](size_type n) const;

      const_reference prefix() const;
      const_reference suffix() const;
      const_iterator begin() const;
      const_iterator end() const;
      const_iterator cbegin() const;
      const_iterator cend() const;

      // 格式
      template<class OutputIt>
        OutputIt
          format(OutputIt out,
                 const char_type* fmt_first, const char_type* fmt_last,
                 regex_constants::match_flag_type flags =
                   regex_constants::format_default) const;
      template<class OutputIt, class ST, class SA>
        OutputIt
          format(OutputIt out,
                 const basic_string<char_type, ST, SA>& fmt,
                 regex_constants::match_flag_type flags =
                   regex_constants::format_default) const;
      template<class ST, class SA>
        basic_string<char_type, ST, SA>
          format(const basic_string<char_type, ST, SA>& fmt,
                 regex_constants::match_flag_type flags =
                   regex_constants::format_default) const;
      string_type
        format(const char_type* fmt,
               regex_constants::match_flag_type flags =
                 regex_constants::format_default) const;

      // 分配器
      allocator_type get_allocator() const;

      // 交换
      void swap(match_results& that);
    };
}