regex_replace

#include <iostream>
#include <string>
#include <boost/regex.hpp>

int main() {
    boost::regex reg("(Colo)(u)(r)", regbase::extended | regbase::icase);

    std::string s="Colour, colours, color, colourize";
    s=boost::regex_replace(s,reg,"$1$3");
    std::cout << s;
}

#g++ test.cpp -lboost_regex
#./a.out
Color, colors, color, colorize