match_results operator= in C++

The match_results::operator= is used to replace all the matches in a smatch object with new matches from another smatch object.
Syntax:

smatch_name1 = (smatch_name2)

Note: smatch_name is an object of match_results class.

Parameters: The smatch object on the right side gets copied to the one at the left side. 
Return Value: It does not return anything. 
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 operator= in C++
#include <bits/stdc++.h>
using namespace std;

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

    smatch match1, match2;

    regex_match(s, match1, re);

    // use of operator =--> assigns all
    // the contents of match1 to match2
    match2 = match1;

    cout << "Matches are:" << endl;
    for (smatch::iterator it = match2.begin();
         it != match2.end(); it++) {
        cout << *it << endl;
    }
}

Output:

Matches are:
Geeksforgeeks
Geeks
forgeeks

Program 2:

CPP

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

int main()
{
    string s("Geeksforgeeks");
    regex re1("(Geeks)(.*)");
    regex re2("(Ge)(eks)(.*)");

    smatch match1, match2;

    regex_match(s, match1, re1);
    regex_match(s, match2, re2);

    smatch max_match;

    // use of operator =--> assigns all
    // the contents of match1 to match2
    if (match1.size() > match2.size()) {
        max_match = match1;
    }
    else {
        max_match = match2;
    }

    cout << "Smatch with maximum matches:" << endl;
    for (smatch::iterator it = max_match.begin();
         it != max_match.end(); it++) {
        cout << *it << endl;
    }
}

Output:

Smatch with maximum matches:
Geeksforgeeks
Ge
eks
forgeeks