Count number of matches

Question

How do I count the number of matches using C++11's std::regex ?

std::regex re("[^\\s]+");
std::cout << re.matches("Harry Botter - The robot who lived.").count() << std::endl;

Expected output:

7

Answer 1

You can use regex_iterator to generate all of the matches, then use distance to count them:

std::regex  const expression("[^\\s]+");
std::string const text("Harry Botter - The robot who lived.");

std::ptrdiff_t const match_count(std::distance(
    std::sregex_iterator(text.begin(), text.end(), expression),
    std::sregex_iterator()));

std::cout << match_count << std::endl;

Answer 2

You can use this:

int countMatchInRegex(std::string s, std::string re)
{
    std::regex words_regex(re);
    auto words_begin = std::sregex_iterator(
        s.begin(), s.end(), words_regex);
    auto words_end = std::sregex_iterator();

    return std::distance(words_begin, words_end);
}

Example usage:

std::cout << countMatchInRegex("Harry Botter - The robot who lived.", "[^\\s]+");

Output:

7