CPP_Regex_01.cpp

#include<iostream>
#include<string>
#include<vector>
#include<regex>
using namespace std;

//Basic grammar
int main(){
    string str;
    while(true){
        cin>>str;
        
        //using regular expression grammar: ECMAScript (default)
        //regex e("^abc.", regex_constants::grep);

        //match string with exactly "abc"
        //regex e("abc"); 

        //match string with "abc", ignore lowercase or uppercase
        //regex e("abc", regex_constants::icase);

        //'.' matches to any character except the newline
        //regex e("abc."); 

        //'?' matches 0 or 1 preceding characters!
        //e.g. "ab", "abc" will be matches
        //regex e("abc?");

        //matches 0 or more preceding characters.
        //regex e("abc*");

        //1 or more preceding characters.
        //regex e("abc+");

        //[...] Any character inside the square brackets, represents 
        //1 character
        //e.g. "abcd", "abc", "abcccddd", "abdcdc" are matches
        //regex e("ab[cd]*"); 

        //[^...] Any character not inside the squre brackets, 
        //represents 1 character
        //regex e("ab[^cd]*");

        //{number} exact match the [number] of preceding characters
        //e.g. "abccc", "abcdd", "abcdc" are matches
        //e.g. "abcdcdcd", "abdddccc", "ab" are not matches
        //regex e("ab[cd]{3}");

        //matches 3 or more preceding characters
        //regex e("ab[cd]{3,}");

        //matches 3, 4 or 5 preceding characters
        //regex e("ab[cd]{3,5}");

        //| - OR
        //e.g. "abc", "def", "deg" are matches
        //"abcd", "defg" are not matches
        //regex e("abc|de[fg]");

        //matches ']'
        //regex e("\]");

        //\1 represents the group 1, the () defines the group
        //e.g. "abcdeeeeabc" is a match
        //regex e("(abc)de+\\1");

        //Note (de+) defines the group, if we have (de+) defined 
        //as "deee", then for group 2, it should always be "deee".
        //regex e("(ab)*c(de+)\\2\\1");

        //matching any e-mail address
        //[[:w:]] word character: digit, number, or underscore!
        //regex e("[[:w:]]+@[[:w:]]+\.com");

        //'^' marks that "abc" should be at the beginning of the string
        //regex e("^abc", regex_constants::icase);

        //'$' marks that "abc." should appear at the end of the string
        regex e("abc.$", regex_constants::icase);

        /*
        [:s:] - a white space character;
        [:w:] - a word character;
        [:d:] - a decimal digit character;
        [:upper:] - an uppercase character;
        [:lower:] - a lowercase character;
        [:alnum:] - an alpha-numerical character;
        [:alpha:] - an alphabetic character;
        [:blank:] - a blank character;
        [:punct:] - a punctuation mark character
         */

        //check whether str can be matched with regular expression e
        bool match = regex_match(str, e);
        //search the string str to see whether there is a substring 
        //of str, that can be matched with e
        bool isFound = regex_search(str, e);

        cout << (match ? "Matched" : "Not matched") << endl << endl;
    }
    return 0;
}