সি++ \B রেজেক্স

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

int main() {

  std::string text = "সি++পাইথন";
  std::regex pattern("\Bপাইথন");

  for (std::sregex_iterator it(text.begin(), text.end(), pattern), end;
    it != end; ++it) {
    std::cout << it->str() << std::endl;
  }
}