match_results cbegin() add cend() in C++ STL

match_results::cbegin() is an inbulit function in C++ STL which returns a constant iterator that points to the first match in the match_results object. This iterator cannot modify the contents of the vector.
Syntax:

smatch_name.cbegin()

Parameters: This function does not accept any parameters.

Return value: This function returns a constant iterator pointing to the first match in the match_results object. The matches contained in the match_results object are always constant.

Note: First element always contains the whole regex match while the others contain the particular Capturing Group.

Below program illustrate the above function.

// C++ program to illustrate the  
// match_result function  
#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    string sp("geeksforgeeks"); 
    regex re("(geeks)(.*)"); 
  
    smatch match; 
  
    // we can use member function on match 
    // to extract the matched pattern. 
    std::regex_match(sp, match, re); 
  
    // The size() member function indicates the 
    // number of capturing groups plus one for the overall match 
    // match size = Number of capturing group + 1 
    // (.*) which "forgeeks" ). 
    cout << "Match size = " << match.size() << endl; 
  
    cout << "matches:" << endl; 
    for (smatch::iterator it = match.cbegin(); it != match.cend(); ++it) 
        cout << *it << endl; 
    return 0; 
} 

Output:

Match size=3
matches:
geeksforgeeks
geeks
forgeeks

smatch::cend() is an inbulit function in C++ STL which returns a constant iterator that points to the past-the-end match in the match_results object. This iterator cannot modify the contents of the vector.

Syntax:

smatch_name.cend()

Parameters: This function does not accept any parameters.

Return value: This function returns a constant iterator pointing to the past-the-end match in the match_results object. The matches contained in the match_results object are always constant.

Note: First element always contains the whole regex match while the others contain the particular Capturing Group.

Below program illustrate the above function

// C++ program to illustrate the  
// match_results cend() function  
#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    string sp("matchresult"); 
    regex re("(match)(.*)"); 
  
    smatch match; 
  
    // we can use member function on match 
    // to extract the matched pattern. 
    std::regex_match(sp, match, re); 
  
    // The size() member function indicates the 
    // number of capturing groups plus one for the overall match 
    // match size = Number of capturing group + 1 
    // (.*) which "results" ). 
    cout << "Match size = " << match.size() << endl; 
  
    cout << "matches:" << endl; 
    for (smatch::iterator it = match.cbegin(); it != match.cend(); ++it) 
        cout << *it << endl; 
    return 0; 
} 

Output:

Match size=3
matches:
matchresults
match
results

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