C中的私有构造函数

现在,当我在main()中有这两行时,

LinkedListIterator iter = list->begin(); <<== No compilation error 
    LinkedListIterator iter2;  <<==== compilation error.

我得到第二行的编译错误,这是默认构造函数是私有的.但是,我不明白为什么第一行没有编译错误？为什么？什么叫代码的第一行？私有构造函数或复制构造函数或赋值运算符？

码

class LinkedListIterator {
    public:
       bool operator== (LinkedListIterator i) const;
       bool operator!= (LinkedListIterator i) const;
       void operator++ (); // Go to the next element
       int& operator* (); // Access the current element
       inline Node* hasnext();
       inline Node* next();

    private:
       LinkedListIterator(Node* p); <<==== Private constructor
       LinkedListIterator();        <<==== Private constructor
       Node* p_;
       friend class LinkedList;//LinkedList can construct a LinkedListIterator

};

....

inline LinkedListIterator::LinkedListIterator(Node* p)
: p_(p)
{ }

inline LinkedListIterator::LinkedListIterator()
{ }

inline LinkedListIterator LinkedList::begin()
{
    return first_;
}

inline LinkedListIterator LinkedList::end()
{
    return NULL;
}

.......

class LinkedList {

public:
    void append(int elem); // Adds elem after the end
    void printList();

    LinkedList() {
        first_ = NULL;
    }

    LinkedListIterator begin();
    LinkedListIterator end();
    LinkedListIterator erase(int elem);

    private:
        Node* first_;

};

main()
{

    LinkedList *list = new LinkedList();

    list->append(1);
    list->append(2);
    list->append(3);

    LinkedListIterator iter = list->begin(); <<== No compilation error 
    LinkedListIterator iter2;  <<==== compilation error.         

}