How to call a class recursively in c++?

Hello this is the code:

template <class T> class FibonacciHeap{
public:
    class Entry{
        public:
            // Returns the element represented by this heap entry.
            T getValue(){
                return mElem;
            }

            // Sets the element associated with this heap entry.
            void setValue(T value){
                    mElem = value;
            }

            // Returns the priority of this element.
            double getPriority(){
                return mPriority;
            }

        private:
            int mDegree = 0;                // Number of children
            bool mIsMarked = false;         // Whether the node is marked

            Entry mNext;                    // Next element in the list
            Entry mPrev;                    // Previous element in the list

            Entry mChild;                   // Child node, if any
            Entry mParent;                  // Parent node, if any
            T mElem;                        // Element being stored here
            double mPriority;               // Its priority

            //Constructs a new Entry that holds the given element with the indicated priority.
            Entry(T elem, double priority){
                mNext = mPrev = this;
                mElem = elem;
                mPriority = priority;
            }
    };
    ...

In the Class "Entry" I want to call Entry recursively, so I can use:

    First_entry.mPrev.mNext

I know this works in Java, but when I compile this in c++, I get:

    error: 'FibonacciHeap<T>::Entry::mNext' has incomplete type

Does anyone know how to fix this or work around this?

Based on the variable names and initializers here, I'm assuming you're adapting my Java Fibonacci heap into C++. :-) If so, best of luck!

In Java, if you have a variable of type Entry, it acts like a C++ variable of type Entry* in that it's a pointer to another Entry object rather than an honest-to-goodness Entry object. As a result, in the definition of the Entry class, you should adjust the fields so that they're of type Entry* rather than Entry. Similarly, instead of using the . operator to select fields, you'll want to use the -> operator. So

First_entry.mPrev.mNext

would be rewritten as

First_entry->mPrev->mNext

Don't forget to explicitly initialize the Entry pointers to nullptr - Java does this automatically, which is why there are no initializers in the Java version. However, C++ gives uninitialized pointers garbage values, so make sure to give mChild and mParent an explicit nullptr value.