問題重載arrow（ - >）operator C++

Question

我有一個自定義容器來存儲數據和一個迭代器來訪問它。問題是迭代器中的 - >運算符不允許我修改容器中的數據。

VALUE_TYPE是一個std ::對<>

數據保持器：

template <class tree> 
struct avl_node { 
private: 
    typedef typename tree::key_type   Key; 
    typedef typename tree::mapped_type  Type; 
    typedef typename tree::value_type  value_type; 
public: 
    typedef avl_node*      node_ptr; 
    typedef const avl_node*     const_node_ptr; 
    node_ptr _parentNode, _leftNode, _rightNode; 
    int _balance; 
    Key first; 
    Type second; 
} 

迭代：

template <class tree> 
class avl_iterator { 
public: 
    typedef typename tree::node    node; 
    typedef typename tree::node_ptr   node_ptr; 
    typedef typename tree::const_node_ptr const_node_ptr; 
    typedef typename tree::utilities  utilities; 
    typedef typename tree::value_type  value_type; 
private: 
    node_ptr _node; 
public: 
    avl_iterator() : _node() { } 
    avl_iterator(const node_ptr node) : _node (node) { } 
    ~avl_iterator() { _node = NULL; } 

    avl_iterator& operator=(const avl_iterator& rhs) { 
     _node = rhs._node; 
     return (*this); 
    } 
    bool operator == (const avl_iterator& rhs) { return (_node == rhs._node); } 
    bool operator != (const avl_iterator& rhs) { return (_node != rhs._node); } 

    avl_iterator& operator++() 
    { 
     _node = utilities::next_node(_node); 
     return (*this); 
    } 
    avl_iterator& operator ++(int) { 
     avl_iterator temp(*this); 
     ++(*this); 
     return(temp); 
    } 

    avl_iterator& operator --() { 
     _node = utilities::prev_node(_node); 
     return (*this); 
    } 

    avl_iterator& operator -- (int) { 
     avl_iterator temp(*this); 
     --(*this); 
     return(temp); 
    } 

    value_type& operator *() { 
     return value_type(node->first, node->second); 
    } 

    node_ptr operator ->() const { 
     return _node; 
    } 
}; 

主

try{ 
    using namespace avl; 
    avltree<int,int> tree; 
    tree.insert(intPair(1,1)); 
    tree.insert(intPair(2,1)); 
    tree.insert(intPair(3,1)); 
    tree.insert(intPair(4,1)); 
    tree.insert(intPair(5,1)); 
    tree.insert(intPair(6,1)); 
    tree.insert(intPair(7,1)); 
    tree.insert(intPair(8,1)); 
    tree.insert(intPair(9,1)); 
    tree.insert(intPair(10,1)); 
    tree.insert(intPair(11,1)); 
    tree.insert(intPair(12,1)); 

    avltree<int,int>::iterator it; 
    //std::map<int,int>::iterator it; 
    for(it = tree.begin(); it != tree.end(); ++it) 
    { 
     std::cout<< it->first << " : "; 
    } 
    std::cout << std::endl; 
    for(it = tree.end(); it != tree.begin(); --it) 
    { 
     std::cout<< it->first << " : "; 
    } 
    std::cout << std::endl; 

      it->first = 5;//shouldnt compile with this line of code, but does 
      it->second = 10; 
} 
catch(...) 
{ 
    std::cout<<"Catch Block\n"; 
} 

Answer 1

這將是更好的有

value_type value; 

在avl_node代替：

Key first; 
Type second; 

然後，您可以在avl_iterator定義：

value_type& operator *() const { 
    return _node->value; 
} 

value_type* operator ->() const { 
    return &_node->value; 
}