title: beginner c++: virtual functions in a base class
body: <p>I'm writing some code where I defined the following base class.</p>
  
  <pre><code>class Chorus{
    public:
  
      //Destructor
      virtual ~Chorus();
  
      //callback function
      virtual int callback( void *outputBuffer, void *notUsed, unsigned int 
         nBufferFrames, double streamTime, RtAudioStreamStatus status, void *userData );
  
      virtual void initializeDelayBuffer(void);
  
      virtual void destroyDelayBuffer(void);
  };
  </code></pre>
  
  <p>I want to use this as a base class and not actually do anything with it on its own. So I have two seperate classes which are derived from this class Chorus. I wanted to do this to simply provide some basic constraints as to what any derived Chorus class <em>MUST</em> have to be considered usable in my program.</p>
  
  <p>When I build my project (Visual Studio 2008), I get unresolved external symbol errors on all the virtual functions from this Chorus class. I'm guessing it's the typical error where I didn't make forward declarations of these functions. But, since they are virtual and I don't want them to actually be defined to do anything until they are defined within the deriving classes, what do I do to resolve this issue?</p>