title: C++11 regex doesn't match the string
body: <p>I want to parse a token that looks like this:</p>
  
  <pre><code>1111111111111111:1384537090:Gl21j08WWBDUCmzq9JZoOXDzzP8=
  </code></pre>
  
  <p>I use a regular expression <code>([0-9]{16}):([0-9]{5,20}):([a-zA-Z0-9\\+/=]{28})</code>, and it does the job when I try it on <a href="http://refiddle.com" rel="nofollow">refiddle</a>. </p>
  
  <p>Then I try it with C++:</p>
  
  <pre><code>std::regex regexp(R"(([0-9]{16}):([0-9]{5,20}):([a-zA-Z0-9\\+/=]{28}))", 
       std::regex_constants::basic);
  std::smatch match;
  
  if (std::regex_search(stringified, match, regexp)) {
      cout &lt;&lt; match[0] &lt;&lt; ',' &lt;&lt; match[1] &lt;&lt; ',' &lt;&lt; match[2] &lt;&lt; endl;
  } else {
      cout &lt;&lt; "No matches found" &lt;&lt; endl;
  }
  </code></pre>
  
  <p>I compile it on Ubuntu 13.10 x64 using GCC 4.8.1 with <code>-std=c++11</code> flag. But I always get <code>No matches found</code>. What am I doing wrong?</p>