title: Pure virtual function with implementation
body: <p>My basic understanding is that there is no implementation for a pure virtual function, however, I was told there might be implementation for pure virtual function. </p>
  
  <pre><code>class A {
  public:
      virtual void f() = 0;
  };
  
  void A::f() {
      cout&lt;&lt;"Test"&lt;&lt;endl;
  }
  </code></pre>
  
  <p>Is code above OK?</p>
  
  <p>What's the purpose to make it a pure virtual function with an implementation?</p>