title: C++ what is "instantiated from here" error?
body: <p>I am new to C++ programming, I am wondering what is "instantiated from here" error? </p>
  
  <pre><code>struct Data {
      Data(int a, int b) {
          x = a;
          y = b;
      }
      int x;
      int y;
  };
  
  std::map&lt;int, Data&gt; m;
  m[1] = Data(1, 2);
  </code></pre>
  
  <p>I got several error messages</p>
  
  <ul>
  <li>no matching function for call to "Data::Data()"</li>
  <li>"instantiated from here" error</li>
  </ul>
  
  <p>Thanks.</p>