C++ regex library doesn't want to match bracket expression repetition

I'm trying to use the C++ regex library. I would expect "aaaaa" to match "[a-z]+", but that is not happening. The code below is exactly that which I am running. When run, it prints nothing. (I would expect it to print "Match!")

#include <regex>
#include <iostream>

int main(int argc, char **argv) {
  std::regex r("[a-z]+", std::regex_constants::basic);

  if ( std::regex_match("aaaaa", r)) {
    std::cout << "Match!" << std::endl;
  }
  return 0;
}

This is my build command:

$ g++ a.cc  -std=c++11

I'm very confused. What do I need to do to make repetitions play nice with bracket expressions?

Notes:

I've tried a few experiments:

• "[:lower:]+" no match

I'm tried [:lower:]. Same result as above. I've also tried "a+". That works fine. "a{3,20}" does not result in a match.