C++: gcc: error was not declared in this scope

Question

Can somebody explain why gcc throws:

lst_iterators.h: In member function â€LST::CIterators::Iterator_Forward& LST::CIterators::Iterator_Forward::operator++()’: lst_iterators.h:77:7: error: â€m_pData’ was not declared in this scope ++m_pData;

1. Everything works properly in VS2017, but gcc complains.
2. As can be seen m_pData is a normal variable in Iterator_Base class, so why can't gcc see the base class?
3. I'm using Centos 7.2 and gcc 6.3.

Any help is appreciated.

Br Waldemar

template <typename itemType> class CIterators
{
    public: class Iterator_Base
    {
    //Constructor/Destructor
        public: Iterator_Base( itemType* pData ) : m_pData( pData )
        {
        };

        protected: itemType*        m_pData;

    //Operators
        public: itemType& operator*()
        {
        //Value operator -> return reference.
            return *m_pData;
        };
        public: bool operator!=( const Iterator_Base& iterator ) const
        {
        //Not equal operator -> compare if not at same pointer.
            return ( m_pData != iterator.m_pData );
        };
    };
    public: class Iterator_Forward : public Iterator_Base
    {
    //Constructor/Destructor
        public: Iterator_Forward( itemType* pData ) : Iterator_Base( pData )
        {
        };

    //Operators
        public: Iterator_Forward& operator++()
        {
        //Increment operator -> go to next value (increase pointer).
            ++m_pData;

        //Return reference.
            return *this;
        };
    };
};

Edit: I still don't understand why gcc doesn't see or know about the base class, but Kerrek's solution works ok.

        public: Iterator_Forward& operator++()
        {
        //Increment operator -> go to next value (increase pointer).
            ++this->m_pData;

        //Return reference.
            return *this;
        };

Edit2: Also found the same issue at Derived template-class access to base-class member-data . Maybe a better solution then this-> is to define which variables are used from base class.

    public: class Iterator_Forward : public Iterator_Base
    {
        protected: using Iterator_Base::m_pData;

    //Constructor/Destructor
        public: Iterator_Forward( itemType* pData ) : Iterator_Base( pData )
        ...