regex.cpp

// Copyright © 2014 Martin Ueding <dev@martin-ueding.de>

#include <iostream>
#include <regex>

int main() {
    std::string haystack {"This\nhas\nnewlines."};
    std::regex regex {"\n"};
    std::string replacement {"\n# "};
    std::string result {std::regex_replace(haystack, regex, replacement)};

    std::cout << "-->" << result << "<--" << std::endl;

    return 0;
}

// $ clang++ -std=c++11 -Wall regex.cpp; and ./a.out 
// --><--