Why doesn't this regex match?

std::cout << std::regex_match(std::string("f 1/1/1 3/3/1 4/4/1"), std::regex("f \d+\/\d+\/\d+ \d+\/\d+\/\d+ \d+\/\d+\/\d+")); // -> 0

What's wrong with this regex ? It does match on http://ift.tt/1uWX1Fo or Notepad++