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 = "Hello Antom";
// Here b is an object of regex (regular expression)
regex b("(Ant)(.*)"); // 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' \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;
}
regex_search() – This function is used to search for a pattern matching the regular expression
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// 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 mad answer"
"articles";
// An object of regex for pattern to be searched
regex r("mad[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:
mad answer
regex_replace() This function is used to replace the pattern matching to the regular expression with a string.
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// 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 MadAnswer\n";
// matches words beginning by "mad"
regex r("Mad[a-zA-z]+");
// regex_replace() for replacing the match with 'geek'
cout << std::regex_replace(s, r, "mad");
string result;
// regex_replace( ) for replacing the match with 'mad'
regex_replace(back_inserter(result), s.begin(), s.end(),
r, "geek");
cout << result;
return 0;
} |
Output:
I am looking for mad
I am looking for mad
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.
