std::sub_match - cppreference.com

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`template< class BidirIt > class sub_match;`		(since C++11)

The class template std::sub_match is used by the regular expression engine to denote sequences of characters matched by marked sub-expressions. A match is a [begin, end) pair within the target range matched by the regular expression, but with additional observer functions to enhance code clarity.

Only the default constructor is publicly accessible. Instances of std::sub_match are normally constructed and populated as a part of a std::match_results container during the processing of one of the regex algorithms.

The member functions return defined default values unless the matched member is true.

std::sub_match inherits from std::pair<BidirIt, BidirIt>, although it cannot be treated as a std::pair object because member functions such as assignment will not work as expected.

Type requirements

Specializations

Several specializations for common character sequence types are provided:

Defined in header `<regex>`
Type	Definition
`std::csub_match`	`std::sub_match<const char*>`
`std::wcsub_match`	`std::sub_match<const wchar_t*>`
`std::ssub_match`	`std::sub_match<std::string::const_iterator>`
`std::wssub_match`	`std::sub_match<std::wstring::const_iterator>`

Nested types

Type	Definition
`iterator`	`BidirIt`
`value_type`	`std::iterator_traits<BidirIt>::value_type`
`difference_type`	`std::iterator_traits<BidirIt>::difference_type`
`string_type`	`std::basic_string<value_type>`

Data members

Member	Description
	whether this match was successful (public member object)

Inherited from std::pair

	start of the match sequence (public member object)
	one-past-the-end of the match sequence (public member object)

Member functions

(constructor)	constructs the match object (public member function) [edit]
Observers
length	returns the length of the match (if any) (public member function) [edit]
stroperator string_type	converts to the underlying string type (public member function) [edit]
compare	compares matched subsequence (if any) (public member function) [edit]
Modifiers
swap	swaps the contents (public member function) [edit]

Non-member functions

Example

#include <cassert>
#include <iostream>
#include <regex>
#include <string>

int main()
{
    std::string sentence{"Friday the thirteenth."};
    const std::regex re{"([A-z]+) ([a-z]+) ([a-z]+)"};
    std::smatch words;
    std::regex_search(sentence, words, re);
    std::cout << std::boolalpha;
    for (const auto& m : words)
    {
        assert(m.matched);
        std::cout << "m: [" << m << "], m.length(): " << m.length() << ", "
                     "*m.first: '" << *m.first << "', "
                     "*m.second: '" << *m.second << "'\n";
    }
}

Output:

m: [Friday the thirteenth], m.length(): 21, *m.first: 'F', *m.second: '.'
m: [Friday], m.length(): 6, *m.first: 'F', *m.second: ' '
m: [the], m.length(): 3, *m.first: 't', *m.second: ' '
m: [thirteenth], m.length(): 10, *m.first: 't', *m.second: '.'