Having trouble instantiating C++ class from objective C

Question

I'm mixing C++ with ObjectiveC for a Cocos2d (objective-C) and Box2D (C++) project.

I have the following C++ class:

class ActorListener : public b2ContactListener
{ 
    public :
    const b2Body* Owner;

    ActorListener(const b2Body* owner);
    ~ActorListener();

    virtual void BeginContact(b2Contact* contact);
    virtual void EndContact(b2Contact* contact);
    virtual void PreSolve(b2Contact* contact, const b2Manifold* oldManifold);    
    virtual void PostSolve(b2Contact* contact, const b2ContactImpulse* impulse);
};

Which I try to initialise with:

(in header)

ActorListener* Listener;

(in mm file)

Listener = new ActorListener(Body);

I get the error:

Undefined symbols for architecture i386:
  "vtable for ActorListener", referenced from:
      ActorListener::ActorListener(b2Body const*)in ActorListener.o
      ActorListener::ActorListener(b2Body const*)in ActorListener.o
ld: symbol(s) not found for architecture i386
collect2: ld returned 1 exit status

rob mayoff · Accepted Answer · 2011-10-30 01:13:30Z

4

The vtable is emitted in the same file as the first virtual function of the class. In this case, ~ActorListener() is the first virtual method, because b2ContactListener::~b2ContactListener() is virtual. Did you remember to define ActorListener::~ActorListener() somewhere?

answered Oct 30, 2011 at 1:13

rob mayoff

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1 Comment

BrendanS Over a year ago

Thanks. There is a very descriptive message when you forget a regular virtual (like the ones I had lower) but that very general one if you forgot destructor.

Ernest Friedman-Hill · Accepted Answer · 2011-10-30 00:31:23Z

0

The trick is to get XCode to use g++ to do the linking. You can force this either by including a C++ source file on the link line -- even a fake, essentially empty one -- or (I think) by explicitly linking with /usr/lib/libstdc++.6.dylib .

answered Oct 30, 2011 at 0:31

Ernest Friedman-Hill

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2 Comments

BrendanS Over a year ago

Can you explain how to do this in more detail? (noob at xcode)

Ernest Friedman-Hill Over a year ago

Literally just including a source file named fake.cpp in your project containing #define FOO 1 will do it.

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