Using regex lookbehinds in C++11

Question

Why can\'t I use lookbehinds in C++11? Lookahead works fine.

std::regex e(\"(?<=a)b\");

This will throw the following exception:

Answer 1

C++11 <regex> uses ECMAScript's (ECMA-262) regex syntax, so it will not have look-behind (other flavors of regex that C++11 supports also doesn't have look-behind).

If your use case requires the use of look-behind, you may consider using Boost.Regex instead.