Using a class variable as a default argument to the class member function

Question

I am building a LinkedList in C++.
Signature for addNode function:

const bool LinkedList::addNode(int val, unsigned int pos = getSize());  

getSize() is a public non-static member function:

int getSize() const { return size; }

size is a non-static private member variable.
However, the error that I am getting is a nonstatic member reference must be relative to a specific object

How do I achieve this functionality?

Just for reference, here's the whole code:

#pragma once

class LinkedList {
    int size = 1;
    struct Node {
        int ivar = 0;
        Node* next = nullptr;
    };
    Node* rootNode = new Node();
    Node* createNode(int ivar);
public:
    LinkedList() = delete;
    LinkedList(int val) {
        rootNode->ivar = val;
    }
    decltype(size) getSize() const { return size; }
    const bool addNode(int val, unsigned int pos = getSize());
    const bool delNode(unsigned int pos);
    ~LinkedList() = default;
};

Some other tries include:

const bool addNode(int val, unsigned int pos = [=] { return getSize(); } ());
const bool addNode(int val, unsigned int pos = [=] { return this->getSize(); } ());
const bool addNode(int val, unsigned int pos = this-> getSize());

---

The current workaround I am currently using:

const bool LinkedList::addNode(int val, unsigned int pos = -1) {
    pos = pos == -1 ? getSize() : pos;
    //whatever
}

Answer 1

The default argument is provided from the caller side context, which just doesn't know which object should be bound to be called on. You can add another wrapper function as

// when specifying pos
const bool LinkedList::addNode(int val, unsigned int pos) {
    pos = pos == -1 ? getSize() : pos;
    //whatever
}

// when not specifying pos, using getSize() instead
const bool LinkedList::addNode(int val) {
    return addNode(val, getSize());
}