Example input
abc55def789KK23GOOD9999910ONEM109ORE19k6 Output
789 109 Example input
abcdef Output
-1 This is what I need to achieve via the regex code.
I have gone through numerous websites for tutorials but couldn't decipher it as needed.
My idea was to use this regex
rx("[0-9][0-9][0-9]""\\-""[0-5][0-5]") But then I couldn't understand the smatch flag and how to retrieve the results.
Here is a sample C++ demo showing how to extract 3 digit chunks not enclosed with other digits:
#include <string> #include <iostream> #include <regex> using namespace std; int main() { std::regex r(R"((?:^|\D)(\d{3})(?!\d))"); std::string s = "abc55def789KK23GOOD9999910ONEM109ORE19k6"; // "abcsd"; => Not Found if (regex_search(s, r)) { for(std::sregex_iterator i = std::sregex_iterator(s.begin(), s.end(), r); i != std::sregex_iterator(); ++i) { std::smatch m = *i; std::cout << m[1].str() << '\n'; } } else { std::cout << "Not found" << '\n'; } return 0; } See the regex demo. The pattern matches:
(?:^|\D) - a start of a string or any non-digit (the (?:...) is a non-capturing group that consumes the text matched with its pattern - we have to use it since C++ std::regex does not support lookbehinds - and thus the following caprturing group ((\d{3})) will have an ID of 1, not 2)(\d{3}) - Group 1: any 3 digits(?!\d) - the 3 digits captured should not be followed with a digit (this (?!...) is a negative lookahead that checks if a pattern matches immediately to the right of the current location without putting the matched text into the match).The m[1].str() is used to access the value captured into Group 1.
rx(R"((?:^|\D)(\d{3})(?!\d))")