Is this C++11 regex error me or the compiler?

Question

Update: <regex> is now implemented and released in GCC 4.9.0

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^{Old answer:}

ECMAScript syntax accepts [0-9], \s, \w, etc, see ECMA-262 (15.10). Here's an example with boost::regex that also uses the ECMAScript syntax by default:

#include <boost/regex.hpp>

int main(int argc, char* argv[]) {
  using namespace boost;
  regex e("[0-9]");
  return argc > 1 ? !regex_match(argv[1], e) : 2;
}

It works:

$ g++ -std=c++0x *.cc -lboost_regex && ./a.out 1

According to the C++11 standard (28.8.2) basic_regex() uses regex_constants::ECMAScript flag by default so it must understand this syntax.

Is this C++11 regex error me or the compiler?

gcc-4.6.1 doesn't support c++11 regular expressions (28.13).

The error is because creating a regex by default uses ECMAScript syntax for the expression, which doesn't support brackets. You should declare the expression with the basic or extended flag:

std::regex r4("[0-9]", std::regex_constants::basic);

Edit Seems like libstdc++ (part of GCC, and the library that handles all C++ stuff) doesn't fully implement regular expressions yet. In their status document they say that Modified ECMAScript regular expression grammar is not implemented yet.

Regex support improved between gcc 4.8.2 and 4.9.2. For example, the regex =[A-Z]{3} was failing for me with:

Regex error

After upgrading to gcc 4.9.2, it works as expected.