std::basic_regex<CharT,Traits>::mark_count (3) - Linux Manuals

std::basic_regex<CharT,Traits>::mark_count: std::basic_regex<CharT,Traits>::mark_count

NAME

std::basic_regex<CharT,Traits>::mark_count - std::basic_regex<CharT,Traits>::mark_count

Synopsis

unsigned mark_count() const; (since C++11)

Returns the number of marked sub-expressions (also known as capture groups) within the regular expression.

Parameters

(none)

Return value

The number of marked sub-expressions within the regular expression.

Exceptions

(none)

Example

// Run this code

  #include <iostream>
  #include <regex>

  int main()
  {
      std::regex r1{"abcde"};
      std::cout << "r1 has " << r1.mark_count() << " subexpressions" << '\n';
      // Expected: 0

      std::regex r2{"ab(c)de"};
      std::cout << "r2 has " << r2.mark_count() << " subexpressions" << '\n';
      // Expected: 1

      std::regex r3{"a(bc)d(e)"};
      std::cout << "r3 has " << r3.mark_count() << " subexpressions" << '\n';
      // Expected: 2

      // nested sub-expressions
      std::regex r4{"abc(de(fg))"};
      std::cout << "r4 has " << r4.mark_count() << " subexpressions" << '\n';
      // Expected: 2

      // escaped parentheses
      std::regex r5{"a(bc\\(\\)de)"};
      std::cout << "r5 has " << r5.mark_count() << " subexpressions" << '\n';
      // Expected: 1

      // using nosubs flag
      std::regex r6 {"ab(c)de", std::regex_constants::nosubs};
      std::cout << "r6 has " << r6.mark_count() << " subexpressions" << '\n';
      // Expected: 0
  }

Output:

  r1 has 0 subexpressions
  r2 has 1 subexpressions
  r3 has 2 subexpressions
  r4 has 2 subexpressions
  r5 has 1 subexpressions
  r6 has 0 subexpressions