regex - C++ primer 5 th ed. matching flag type

Question

I have this exercise from C++ primer 5th ed.

Exercise 17.26: Rewrite your phone program so that it writes only the second and subsequent phone numbers for people with more than one phone number.

my solution for the previous exercise: A program for finding the first match and format it using the formatting string fmt and output only the first number:

int main(){

    std::string pattern = "(\()?(\d{3})(\))?([-. ])?(\d{3})([-. ])?(\d{4})";
    std::regex reg(pattern);
    std::string fmt = "$2.$5.$7 ";

    for(std::string line; std::getline(std::cin, line); )
        std::cout << std::regex_replace(line, reg, fmt, format_first_only | format_no_copy) << '
';

}

Input:

 morgan (201) 555-2368 862-555-0123
 drew (973)555.0130
 lee (609) 555-0132 2015550175 800.555-0000

Output:

201.555.2368
973.555.0130
609.555.0132

• AS you can see it formats the first match only and outputs it. So How can I format and output all the matches but the first? I find it a bit difficult to achieve since there's no Matching Flag Type as format_second...?

question from:https://stackoverflow.com/questions/65946053/c-primer-5-th-ed-matching-flag-type

Answer 1

It is a bit tricky: you need to get rid off the first match then apply the matching flag: std::regex_constants::format_no_copyinto std::regex_replace:

• std::sregex_iterator is your choice because it can be initialized to denote the first match then we use its member: suffix().str() passing it to std::regex_replace:

    int main(){
  
        std::string pattern = "(\()?(\d{3})(\))?([-. ])?(\d{3})([-. ])?(\d{4})";
        std::regex reg(pattern);
        std::string fmt = "$2.$5.$7 ";
  
        for(std::string line; std::getline(std::cin, line); ){
            // it points to the first match (phone number)
            std::sregex_iterator it(line.cbegin(), line.cend(), reg);
            // we use suffix as the input sequence skipping the first match
            std::cout << std::regex_replace(it->suffix().str(), reg, fmt, format_no_copy) << '
  ';
        }
    }
  

Input:

 morgan (201) 555-2368 862-555-0123
 drew (973)555.0130
 lee (609) 555-0132 2015550175 800.555-0000

Output:

862.555.0123

201.555.0175 800.555.0000