title: what is the problem of this code in c++
body: <pre><code>template &lt;typename T&gt;
  class Foo {
      T tVar;
      public:
      Foo(T t):tVar() {}
  };
  
  class FooDerived: public Foo&lt;std::string&gt; {};
  
  FooDerived fd;
  </code></pre>
  
  <p>what is the problem of this code?</p>