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std::regex_match, std::regex_replace() | Regex (Regular Expression) In C++

Regex is the short form for “Regular expression”, which is often used in this way in programming languages and many different libraries. It is supported in C++11 onward compilers.

Function Templates used in regex

regex_match() -This function return true if the regular expression is a match against the given string otherwise it returns false.

// C++ program to demonstrate working of regex_match()
#include <iostream>
#include <regex>
  
using namespace std;
int main()
{
    string a = "GeeksForGeeks";
  
    // Here b is an object of regex (regular expression)
    regex b("(Geek)(.*)"); // Geeks followed by any character
  
    // regex_match function matches string a against regex b
    if ( regex_match(a, b) )
        cout << "String 'a' matches regular expression 'b' ";
  
    // regex_match function for matching a range in string 
    // against regex b
    if ( regex_match(a.begin(), a.end(), b) )
        cout << "String 'a' matches with regular expression "
                "'b' in the range from 0 to string end ";
  
    return 0;
}

Output:

String 'a' matches regular expression 'b' 
String 'a' matches with regular expression 'b' in the range from 0 to string end

 
regex_search() – This function is used to search for a pattern matching the regular expression



// C++ program to demonstrate working of regex_search()
#include <iostream>
#include <regex>
#include<string.h>
using namespace std;
  
int main()
{
    // Target sequence
    string s = "I am looking for GeeksForGeeks "
               "articles";
  
    // An object of regex for pattern to be searched
    regex r("Geek[a-zA-Z]+");
  
    // flag type for determining the matching behavior
    // here it is for matches on 'string' objects
    smatch m;
  
    // regex_search() for searching the regex pattern
    // 'r' in the string 's'. 'm' is flag for determining
    // matching behavior.
    regex_search(s, m, r);
  
    // for each loop
    for (auto x : m)
        cout << x << " ";
  
    return 0;
}

Output:

GeeksForGeeks

 

regex_replace() This function is used to replace the pattern matching to the regular expression with a string.

// C++ program to demonstrate working of regex_replace()
#include <iostream>
#include <string>
#include <regex>
#include <iterator>
using namespace std;
  
int main()
    string s = "I am looking for GeeksForGeek ";
      
    // matches words beginning by "Geek"
    regex r("Geek[a-zA-z]+");
      
    // regex_replace() for replacing the match with 'geek' 
    cout << std::regex_replace(s, r, "geek");
      
    string result;
      
    // regex_replace( ) for replacing the match with 'geek'
    regex_replace(back_inserter(result), s.begin(), s.end(),
                  r,  "geek");
  
    cout << result;
  
    return 0;
}

Output:

I am looking for geek 
I am looking for geek

So Regex operations make use of following parameters :-

  • Target sequence (subject) – The string to be matched.
  • Regular Expression (Pattern) – The regular expression for the target sequence.
  • Matched Array – The information about matches is stored in a special match_result array.
  • Replacement String – These string are used for allowing replacement of the matches.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



This article is attributed to GeeksforGeeks.org

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