I have installed and built Boost (1.35.0) on my Mac, and things are working beautifully when I create a "pure" C++ project. My test source file looks like this: #include <iostream> #include #include <string> int main (int argc, char * const argv[]) { std::string expr = std::string("(Colo)(u)(r)"); std::string textToMatch = std::string("Colour, colorize, colours, color"); boost::regex reg(expr, boost::regex::icase | boost::regex::perl); std::string result = regex_replace(textToMatch, reg, "$1$3"); std::cout << result; return 0; } It runs and produces the expected output. However, my intent is to use Boost in a project combined with Objective-C code. When I use the exact same code in a file called Test.mm and try to compile in XCode, I get compiler errors in cpp_regex_traits.hpp end perl_matcher_hpp: error: cannot find protocol declaration for "" - in line 799 of cpp_regex_traits error: expected unqualified-id before '=' token - in lines 259 and 265 of perl_matcher.hpp I am sure it is just some compiler flag I need to set somewhere, but at the moment I am stumped. Has anyone reading this list successfully mixed objective-c with c++ and the boost library? Sincerely, Helge