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.

CPP

// 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)(.*)"); // Geek 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' \n";

    // 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\n";

    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 

CPP

// 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.

CPP

// 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 \n";

    // 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.

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