title: std::regex throws Microsoft C++ exception: std::regex_error at memory location on runtime
body: <p>In the last two hours I've tried to understand why the line of code from below</p>
  
  <pre><code>std::regex matchPattern{R"(?&lt;=\@)(.*?)(?=\=)"};
  </code></pre>
  
  <p>throws <strong>Microsoft C++ exception: std::regex_error at memory location ....</strong></p>
  
  <p>I've tested the regular expresion with online tools and notepad++ and everything works just fine. When I'm trying to use it in my c++ app  I get the runtime error from above on initialization. 
  I am using c++14</p>
  
  <p>Thanks in advance for your help. </p>