in .cpp file

class LLOpenTaskOffer : public LLInventoryAddedObserver
{

public:
        LLOpenTaskOffer()
        {
                gInventory.addObserver(this);
        }
        virtual ~LLOpenTaskOffer() {}
protected:
        virtual void done()
        {
                llinfos << "TaskOffer Done entry" << llendl;
                open_offer(mAdded);
        }

};

LLOpenTaskOffer* gOpenTaskOffer = new LLOpenTaskOffer;

inventory_callback()
{
...
 gOpenTaskOffer->incrementCount();
...
}