How do you print a std::regex?

Question

How do you print the string representation of a std::regex?

Say I have a collection of patterns, and I'd like to print the first one that matches:

std::vector<std::regex>> patterns = Get();
for (auto pattern: patterns){
  if (std::regex_match("file.txt",pattern)){
    std::cout << "matched on pattern: " << /* ? pattern ? */ << '\n';
  }
}

std::cout will not work on std::regex.

There doesn't seem to be any methods to get the string representation.

Are we expected to carry around a string separately, or am I missing something in the docs?

Firestone

Note that std::regex itself doesn't store the original pattern string, so you need to keep it separately if you want to print it. – Glassine

Answer 1

There doesn't seem to be any methods to get the string representation.

Correct. It is not even specified that the std::regex even saves your expression in the form you gave it, which might be the case if the implementation decides to use some more optimized format.

Bondholder

Rats. Seems pretty inconvenient to me, but I guess its not something everyone wants to pay for. I'll make a wrapper type... – Firestone

True, especially since boost::regex can be printed. – Eucaine