Program to find all match of a regex in a string

Prerequisite: smatch | Regex (Regular Expressions) in C++

Given a regex, the task is to find all regex matches in a string.

  • Without using iterator:
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // C++ program to find all the matches
    #include <bits/stdc++.h>
    using namespace std;
    int main()
    {
        string subject("My GeeksforGeeks is my " 
                        "GeeksforGeeks none of your GeeksforGeeks");
      
        // Template instantiations for
        // extracting the matching pattern.
        smatch match;
        regex r("GeeksforGeeks");
        int i = 1;
        while (regex_search(subject, match, r)) {
            cout << "\nMatched string is " << match.str(0) << endl
                 << "and it is found at position " 
                 << match.position(0)<<endl; 
            i++;
      
            // suffix to find the rest of the string.
            subject = match.suffix().str();
        }
        return 0;
    }

    chevron_right

    
    

    Output:

    Matched string is GeeksforGeeks
    and it is found at position 3
    
    Matched string is GeeksforGeeks
    and it is found at position 7
    
    Matched string is GeeksforGeeks
    and it is found at position 14
    

    Note: Above code is running perfectly fine but the problem is input string will be lost.

  • Using iterator:
    Object can be constructed by calling the constructor with three parameters: a string iterator indicating the starting position of the search, a string iterator indicating the ending position of the search, and the regex object. Construct another iterator object using the default constructor to get an end-of-sequence iterator.

    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    #include <bits/stdc++.h>
    using namespace std;
    int main()
    {
        string subject("geeksforgeeksabcdefghg"
                       "eeksforgeeksabcdgeeksforgeeks");
      
        // regex object.
        regex re("geeks(for)geeks");
      
        // finding all the match.
        for (sregex_iterator it = sregex_iterator(subject.begin(), subject.end(), re);
             it != sregex_iterator(); it++) {
            smatch match;
            match = *it;
            cout << "\nMatched  string is = " << match.str(0)
                 << "\nand it is found at position "
                 << match.position(0) << endl;
            cout << "Capture " << match.str(1)
                 << " at position " << match.position(1) << endl;
        }
        return 0;
    }

    chevron_right

    
    

    Output:

    Matched  string is = geeksforgeeks
    and it is found at position 0
    Capture for at position 5
    
    Matched  string is = geeksforgeeks
    and it is found at position 21
    Capture for at position 26
    
    Matched  string is = geeksforgeeks
    and it is found at position 38
    Capture for at position 43
    

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.




My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.