title: undefined reference to 'vtable for class' constructor
body: <p>I am getting an undefined reference to `vtable for student' while compiling the following header file:</p>
  
  <p>student.h</p>
  
  <pre><code>class student
  {
  private:
      string names;
      string address;
      string type;
  
  protected:
      float marks;
      int credits;
  
  public:
      student();
      student(string n,string a,string t,float m);
      ~student();
      string getNames();
      string getAddress();
      string getType();
      float getMarks();
      virtual void calculateCredits();
      int getCredits();
  };
  
  student::student(){}
  
  student::student(string n, string a,string t,float m)
  {
      names = n;
      address = a;
      marks = m;
  }
  
  student::~student(){}
  </code></pre>
  
  <p>I can't find what is wrong in this.</p>