std::sub_match

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Text processing library

Localization library

Regular expressions library (C++11)

Formatting library (C++20)

Null-terminated sequence utilities

Byte strings

Multibyte strings

Wide strings

Primitive numeric conversions

to_chars (C++17) to_chars_result (C++17) from_chars (C++17) from_chars_result (C++17) chars_format (C++17)

Text encoding identifications

text_encoding (C++26)

 

Regular expressions library

Classes

basic_regex (C++11)

sub_match (C++11)

match_results (C++11)

Algorithms

regex_match (C++11)

regex_search (C++11)

regex_replace (C++11)

Iterators

regex_iterator (C++11)

regex_token_iterator (C++11)

Exceptions

regex_error (C++11)

Traits

regex_traits (C++11)

Constants

syntax_option_type (C++11)

match_flag_type (C++11)

error_type (C++11)

Regex Grammar

Modified ECMAScript-262 (C++11)

 

std::sub_match

Member functions

sub_match::sub_match

sub_match::length

sub_match::strsub_match::operator string_type

sub_match::compare

sub_match::swap

Non-member functions

operator==operator!=operator<<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

operator<<

 

Defined in header <regex>
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

- BidirIt must meet the requirements of LegacyBidirectionalIterator.

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
bool matched	whether this match was successful (public member object)

Inherited from std::pair

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

Member functions

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

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (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)
operator<<	outputs the matched character subsequence (function template)

Example

Run this code

#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: '.'

See also

regex_token_iterator (C++11)

iterates through the specified sub-expressions within all regex matches in a given string or through unmatched substrings (class template)