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

Last Updated : 04 Jul, 2022

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.

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

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

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