NAME

std::basic_regex::mark_count - std::basic_regex::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

May throw implementation-defined exceptions.

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