Subclassing CgiInput

Hello @All.
I hope anyone can help me on this topic. I'm trying to use the cgicc library in a FastCgi environment. Therefore I want to subclass CgiInput as described in the cgicc documentation. My FastCgiInput class looks as follows:

        class FastCgiInput
         : public cgicc::CgiInput {

        friend class FastCgiManager;

        private:
                FastCgiInput();
                FastCgiInput(const FastCgiInput & anOriginal);

        public:
                virtual
                ~FastCgiInput();

        public:
                virtual
                size_t
                read(char * Data, size_t aLength) const;

                virtual
                std::string
                getenv(const char * aName) const;

        };

The constructor is private, because only the methods of the friend class FastCgiManager should be able to create FastCgiInput objects. It has no effect, if I change the constructors to be public. However, the behaviour is not the desired one: It is possible to create a new object of type FastCgiInput and the overloaded methods read and getenv work fine, if called directly on the created object. But it is impossible to create an object of type CgiEnvironment by passing a FastCgiInput object to the constructor. If doing so, the CgiEnvironment seems not to be able to read out the environment variables. As an illustration:

FastCgiInput *   i = new FastCgiInput();
CgiEnvironment * e = new CgiEnvironment(i);

A call to i->getenv("QUERY_STRING") is successful and returns the right query string, but a call to e->getQueryString() returns an empty string.

The documentation says, that the operator= must be overloaded. What exactly does that mean? What signature should I use when overloading operator=? How does this affect the behaviour of the code?

Thanks,
Matthias