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

Last Updated : 4 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 #include

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 #include #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;

}

`

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 #include #include #include 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 :