[re.submatch]

# 28 Text processing library [[text]](./#text)

## 28.6 Regular expressions library [[re]](re#submatch)

### 28.6.8 Class template sub_match [re.submatch]

#### [28.6.8.1](#general) General [[re.submatch.general]](re.submatch.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10835)

Class template sub_match denotes the sequence of characters matched
by a particular marked sub-expression[.](#general-1.sentence-1)

namespace std {template<class BidirectionalIterator>class sub_match : public pair<BidirectionalIterator, BidirectionalIterator> {public:using value_type =typename iterator_traits<BidirectionalIterator>::value_type; using difference_type =typename iterator_traits<BidirectionalIterator>::difference_type; using iterator = BidirectionalIterator; 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(*see below*); };}

#### [28.6.8.2](#members) Members [[re.submatch.members]](re.submatch.members)

[🔗](#lib:sub_match,constructor)

`constexpr sub_match();
`

[1](#members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10878)

*Effects*: Value-initializes the pair base class subobject and the membermatched[.](#members-1.sentence-1)

[🔗](#lib:sub_match,length)

`difference_type length() const;
`

[2](#members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10890)

*Returns*: matched ? distance(first, second) : 0[.](#members-2.sentence-1)

[🔗](#lib:operator_basic_string,sub_match)

`operator string_type() const;
`

[3](#members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10901)

*Returns*: matched ? string_type(first, second) : string_type()[.](#members-3.sentence-1)

[🔗](#lib:sub_match,str)

`string_type str() const;
`

[4](#members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10912)

*Returns*: matched ? string_type(first, second) : string_type()[.](#members-4.sentence-1)

[🔗](#lib:sub_match,compare)

`int compare(const sub_match& s) const;
`

[5](#members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10923)

*Returns*: str().compare(s.str())[.](#members-5.sentence-1)

[🔗](#lib:sub_match,compare_)

`int compare(const string_type& s) const;
`

[6](#members-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10934)

*Returns*: str().compare(s)[.](#members-6.sentence-1)

[🔗](#lib:sub_match,compare__)

`int compare(const value_type* s) const;
`

[7](#members-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10945)

*Returns*: str().compare(s)[.](#members-7.sentence-1)

[🔗](#lib:sub_match,swap)

`void swap(sub_match& s) noexcept(see below);
`

[8](#members-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10956)

*Preconditions*: BidirectionalIterator meets
the *Cpp17Swappable* requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#members-8.sentence-1)

[9](#members-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10961)

*Effects*: Equivalent to:this->pair<BidirectionalIterator, BidirectionalIterator>::swap(s);
std::swap(matched, s.matched);

[10](#members-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10969)

*Remarks*: The exception specification is equivalent tois_nothrow_swappable_v<BidirectionalIterator>[.](#members-10.sentence-1)

#### [28.6.8.3](#op) Non-member operators [[re.submatch.op]](re.submatch.op)

[1](#op-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10977)

Let *SM-CAT*(I) becompare_three_way_result_t<basic_string<typename iterator_traits<I>::value_type>>

[🔗](#lib:sub_match,operator==)

`template<class BiIter>
  bool operator==(const sub_match<BiIter>& lhs, const sub_match<BiIter>& rhs);
`

[2](#op-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L10990)

*Returns*: lhs.compare(rhs) == 0[.](#op-2.sentence-1)

[🔗](#lib:sub_match,operator%3c=%3e)

`template<class BiIter>
  auto operator<=>(const sub_match<BiIter>& lhs, const sub_match<BiIter>& rhs);
`

[3](#op-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11002)

*Returns*: static_cast<*SM-CAT*(BiIter)>(lhs.compare(rhs) <=> 0)[.](#op-3.sentence-1)

[🔗](#lib:operator==,sub_match_)

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

[4](#op-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11016)

*Returns*: lhs.compare(typename sub_match<BiIter>::string_type(rhs.data(), rhs.size())) == 0

[🔗](#lib:operator%3c=%3e,sub_match_)

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

[5](#op-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11032)

*Returns*: static_cast<*SM-CAT*(BiIter)>(lhs.compare(typename sub_match<BiIter>::string_type(rhs.data(), rhs.size()))<=> 0)

[🔗](#lib:sub_match,operator==__)

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

[6](#op-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11050)

*Returns*: lhs.compare(rhs) == 0[.](#op-6.sentence-1)

[🔗](#lib:sub_match,operator%3c=%3e__)

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

[7](#op-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11063)

*Returns*: static_cast<*SM-CAT*(BiIter)>(lhs.compare(rhs) <=> 0)[.](#op-7.sentence-1)

[🔗](#lib:sub_match,operator==___)

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

[8](#op-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11076)

*Returns*: lhs.compare(typename sub_match<BiIter>​::​string_type(1, rhs)) == 0[.](#op-8.sentence-1)

[🔗](#lib:sub_match,operator%3c=%3e___)

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

[9](#op-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11089)

*Returns*: static_cast<*SM-CAT*(BiIter)>(lhs.compare(typename sub_match<BiIter>::string_type(1, rhs))<=> 0)

[🔗](#lib:basic_ostream)

`template<class charT, class ST, class BiIter>
  basic_ostream<charT, ST>&
    operator<<(basic_ostream<charT, ST>& os, const sub_match<BiIter>& m);
`

[10](#op-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L11108)

*Returns*: os << m.str()[.](#op-10.sentence-1)