match_results size() in C++ STL

The match_results size() is a inbuilt function in C++ which returns the number of matches ans sub-matches in the match_result object.
Syntax:

smatch_name.size()

Note: smatch_name is an object of match_results class.

Parameters: The function accept no parameters.
Return value: It returns the number of matches in the match_result object.
Note: First element always contains the whole regex match while the others contain the particular Capturing Group
Below programs illustrate the above function.
Program 1:

CPP

// CPP program to illustrate
// match_results size() in C++
#include <bits/stdc++.h>
using namespace std;

int main()
{
    string s("Geeksforgeeks");
    regex re("(Geeks)(.*)");

    smatch match;

    // Function call to find match
    regex_match(s, match, re);

    cout << "match size is " << match.size() << endl;

    return 0;
}

Output:

match size is 3

Program 2:

CPP

// CPP program to illustrate
// match_results size() in C++
#include <bits/stdc++.h>
using namespace std;

int main()
{
    string s("Geeksforgeeks");
    regex re("(Geeks)(.*)");

    smatch match;

    // Function call to find matches
    regex_match(s, match, re);

    cout << "match size is " << match.size() << endl;

    for (int i = 0; i < match.size(); i++) {
        cout << "match " << i << " has a length of "
             << match.length(i) << endl;
    }
    return 0;
}

Output:

match size is 3
match 0 has a length of 13
match 1 has a length of 5
match 2 has a length of 8