c 2b 2b get string between two characters

1string str = "STARTDELIMITER_0_192.168.1.18_STOPDELIMITER";
2unsigned first = str.find(STARTDELIMITER);
3unsigned last = str.find_last_of(STOPDELIMITER);
4string strNew = str.substr (first,last-first);
5std::cout << strNew << std::endl;