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Standard library header <regex> (C++11)

This header is part of the regular expressions library.

Includes
(C++20)
 Three-way comparison operator support
(C++11)
 std::initializer_list class template

Classes
(C++11)
 regular expression object
(class template)
std::regex std::basic_regex<char> (typedef)
std::wregex std::basic_regex<wchar_t> (typedef)
(C++11)
 identifies the sequence of characters matched by a sub-expression
(class template)
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)
(C++11)
 identifies one regular expression match, including all sub-expression matches
(class template)
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)
(C++11)
 iterates through all regex matches within a character sequence
(class template)
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)
(C++11)
 iterates through the specified sub-expressions within all regex matches in a given string or through unmatched substrings
(class template)
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)
(C++11)
 reports errors generated by the regular expressions library
(class)
(C++11)
 provides metainformation about a character type, required by the regex library
(class template)
regex constant types
Defined in namespace std::regex_constants
(C++11)
 general options controlling regex behavior
(typedef)
(C++11)
 options specific to matching
(typedef)
(C++11)
 describes different types of matching errors
(typedef)

Functions
Algorithm
(C++11)
 attempts to match a regular expression to an entire character sequence
(function template)
(C++11)
 attempts to match a regular expression to any part of a character sequence
(function template)
(C++11)
 replaces occurrences of a regular expression with formatted replacement text
(function template)
Non-member operations
(C++11)
 specializes the std::swap algorithm
(function template)
(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)
 compares a sub_match with another sub_match, a string, or a character
(function template)
outputs the matched character subsequence
(function template)
(removed in C++20)
 lexicographically compares the values in the two match result
(function template)
(C++11)
 specializes the std::swap algorithm
(function template)
Range access
(C++11)(C++14)
 returns an iterator to the beginning of a container or array
(function template)
(C++11)(C++14)
 returns an iterator to the end of a container or array
(function template)
(C++14)
 returns a reverse iterator to the beginning of a container or array
(function template)
(C++14)
 returns a reverse end iterator for a container or array
(function template)
(C++17)(C++20)
 returns the size of a container or array
(function template)
(C++17)
 checks whether the container is empty
(function template)
(C++17)
 obtains the pointer to the underlying array
(function template)

Synopsis

#include <compare>
#include <initializer_list>
 
namespace std {
  // regex constants
  namespace regex_constants {
    using syntax_option_type = /*T1*/;
    using match_flag_type = /*T2*/;
    using error_type = /*T3*/;
  }
 
  // class regex_error
  class regex_error;
 
  // class template regex_traits
  template<class CharT> struct regex_traits;
 
  // class template 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 swap
  template<class CharT, class Traits>
    void swap(basic_regex<CharT, Traits>& e1, basic_regex<CharT, Traits>& e2);
 
  // class template 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 non-member operators
  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);
 
  // class template 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 comparisons
  template<class BiIt, class Allocator>
    bool operator==(const match_results<BiIt, Allocator>& m1,
                    const match_results<BiIt, Allocator>& m2);
 
  // match_results swap
  template<class BiIt, class Allocator>
    void swap(match_results<BiIt, Allocator>& m1, match_results<BiIt, Allocator>& m2);
 
  // function template 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);
 
  // function template 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;
 
  // function template 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);
 
  // class template 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>;
 
  // class template 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>;
  }
}

Bitmask type std::regex_constants::syntax_option_type 

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

Bitmask type 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 = /* unspecified */;
  inline constexpr match_flag_type match_not_eol = /* unspecified */;
  inline constexpr match_flag_type match_not_bow = /* unspecified */;
  inline constexpr match_flag_type match_not_eow = /* unspecified */;
  inline constexpr match_flag_type match_any = /* unspecified */;
  inline constexpr match_flag_type match_not_null = /* unspecified */;
  inline constexpr match_flag_type match_continuous = /* unspecified */;
  inline constexpr match_flag_type match_prev_avail = /* unspecified */;
  inline constexpr match_flag_type format_default = {};
  inline constexpr match_flag_type format_sed = /* unspecified */;
  inline constexpr match_flag_type format_no_copy = /* unspecified */;
  inline constexpr match_flag_type format_first_only = /* unspecified */;
}

Enumerated type std::regex_constants::error_type 

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

Class 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;
  };
}

Class template 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 = /* bitmask-type */;
 
      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;
    };
}

Class template std::basic_regex 

namespace std {
  template<class CharT, class Traits = regex_traits<CharT>>
    class basic_regex {
    public:
      // types
      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;
 
      // constants
      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;
 
      // construct/copy/destroy
      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();
 
      // assign
      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 operations
      unsigned mark_count() const;
      flag_type flags() const;
 
      // locale
      locale_type imbue(locale_type loc);
      locale_type getloc() const;
 
      // swap
      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>;
}

Class template 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;
    };
}

Class template 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  = /* implementation-defined */;
      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>;
 
      // construct/copy/destroy
      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();
 
      // state
      bool ready() const;
 
      // size
      size_type size() const;
      size_type max_size() const;
      [[nodiscard]] bool empty() const;
 
      // element access
      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;
 
      // format
      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;
 
      // allocator
      allocator_type get_allocator() const;
 
      // swap
      void swap(match_results& that);
    };
}

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