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)(.*)" ); // 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;
} |
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;
} |
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 \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;
} |
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.