如何在类中使用重载的const_iterator？

class MyClass {
private:
    int data[5] = {1, 2, 3, 4, 5};

public:
    class iterator {
    private:
        int* ptr;

    public:
        iterator(int* p) : ptr(p) {}

        iterator& operator++() {
            ++ptr;
            return *this;
        }

        iterator& operator--() {
            --ptr;
            return *this;
        }

        int& operator*() const {
            return *ptr;
        }
    };

    iterator begin() {
        return iterator(data);
    }

    iterator end() {
        return iterator(data + 5);
    }

    class const_iterator : public iterator {
    public:
        const_iterator(int* p) : iterator(p) {}

        const int& operator*() const {
            return *iterator::ptr;
        }
    };

    const_iterator cbegin() const {
        return const_iterator(data);
    }

    const_iterator cend() const {
        return const_iterator(data + 5);
    }
};

int main() {
    MyClass obj;

    // 使用iterator遍历
    for (auto it = obj.begin(); it != obj.end(); ++it) {
        *it = 0;  // 修改值
        std::cout << *it << " ";  // 输出值
    }
    std::cout << std::endl;

    // 使用const_iterator只读遍历
    for (auto it = obj.cbegin(); it != obj.cend(); ++it) {
        // *it = 0;  // 错误，只读访问无法修改值
        std::cout << *it << " ";  // 输出值
    }
    std::cout << std::endl;

    return 0;
}