C++ regex character classes [duplicate]

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• Is gcc4.7 buggy about regular expressions? 1 answer

Trying to create a std::regex object with a []-enclosed character class in C++ I am getting an error:

std::regex re0("\\.");
std::regex re1("a");
std::regex re2("a+");
std::regex re3("a*");
std::regex re4("[az]");  // fails
std::regex re5("[a-z]");  // fails

This results in the following error:

unknown file: Failure
C++ exception with description "regex_error"

I am using gcc version 4.8.2.

The syntax seems correct according to the reference and works in other regex compilers (I tried Python's re and regex101.com). How can I create a regular expression object for a range character class in C++?