match_results length() in C++ STL

In this article we will be discussing the working, syntax and examples of match_results::length() function in C++ STL.

What is a match_results in C++ STL?

std::match_results is a specialized container-like class which is used to hold the collection of character sequences which are matched. In this container class a regex match operation finds the matches of the target sequence.

What is match_results::length()?

match_results::length() function is an inbuilt function in C++ STL, which is defined in <regex> header file. length() is used to check the length of the n-th match in the match_results object associated with it. length() accepts a parameter which is the match number which should be less than match_results::size(), for checking the length of the nth match.

Syntax

smatch_name.length(unsigned int num);

Parameters

This function accepts one parameter which is the match number which should be lower than the size of the container. Match number 0 represents the entire match expression.

Return value

This function returns unsigned integer value of the number of matches in the object

Example

Input: std::smatch;
   smatch.length(0);
Output: 0

Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int main() {
   string str = "TutorialsPoint";
   regex R("(Tutorials)(.*)");
   smatch Mat;
   regex_match(str, Mat, R);
   for (int i = 0; i < Mat.size(); i++) {
      cout<<"Match is : " << Mat[i]<< endl;
   }
   return 0;
}

Output

If we run the above code it will generate the following output −

Match is : TutorialsPoint
Match is : Tutorials
Match is : Point

Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int main() {
   string sr = "Tutorials Point";
   regex Re("(Tutorials)(.*)");
   smatch Mat;
   regex_match(sr, Mat, Re);
   int len = 0;
   string str;
   for (int i = 1; i < Mat.size(); i++) {
      if (Mat.length(i) > len) {
         str = Mat[i];
         len = Mat.length(i);
      }
   }
   cout<<"Match length is of: " << len;
   return 0;
}