STL源码剖析——关联容器之multimap

╰半橙微兮° 2022-08-12 12:59 164阅读 0赞

## 前言 ##

multimap的特性及其用法和map完全相同，唯一的区别就是multimap允许键值key重复，因此multimap的插入操作采用的是底层RB-Tree的insert\_equal()而非insert\_unique()，有关map容器的介绍前往博文《[关联容器之map][map]》。本文的源码出自SGI STL中的<stl\_multimap.h>文件。

## multimap容器源码剖析 ##

#ifndef __SGI_STL_INTERNAL_MULTIMAP_H
    #define __SGI_STL_INTERNAL_MULTIMAP_H
    
    #include <concept_checks.h>
    
    __STL_BEGIN_NAMESPACE
    
    #if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
    #pragma set woff 1174
    #pragma set woff 1375
    #endif
    
    // Forward declaration of operators < and ==, needed for friend declaration.
    
    //multimap的特性及其用法和map完全相同，唯一的区别就是multimap允许键值key重复
    //因此multimap的插入操作采用的是底层RB-Tree的insert_equal()而非insert_unique()
    //有关map容器的剖析见前面博文
    //map内部元素根据键值key默认使用递增排序less
    //用户可自行制定比较类型
    //内部维护的数据结构是红黑树, 具有非常优秀的最坏情况的时间复杂度
    //注意:multimap允许元素重复,即键值和实值都可以重复,这点与map不同
    template <class _Key, class _Tp, 
              class _Compare __STL_DEPENDENT_DEFAULT_TMPL(less<_Key>),
              class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp) >
    class multimap;
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator==(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const multimap<_Key,_Tp,_Compare,_Alloc>& __y);
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator<(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const multimap<_Key,_Tp,_Compare,_Alloc>& __y);
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    class multimap {
      // requirements:
    
      __STL_CLASS_REQUIRES(_Tp, _Assignable);
      __STL_CLASS_BINARY_FUNCTION_CHECK(_Compare, bool, _Key, _Key);
    
    public:
    
    // typedefs:
    
      //下面的定义与map相同
      typedef _Key                  key_type;
      typedef _Tp                   data_type;
      typedef _Tp                   mapped_type;
      typedef pair<const _Key, _Tp> value_type;
      typedef _Compare              key_compare;
    
       //嵌套类,提供键值key比较函数接口
      //继承自<stl_function.h>中的binary_function
      /*
    	template <class _Arg1, class _Arg2, class _Result>
    	struct binary_function {
    		typedef _Arg1 first_argument_type;
    		typedef _Arg2 second_argument_type;
    		typedef _Result result_type;
    	}; 
      */
      class value_compare : public binary_function<value_type, value_type, bool> {
      friend class multimap<_Key,_Tp,_Compare,_Alloc>;
      protected:
        _Compare comp;
        value_compare(_Compare __c) : comp(__c) {}
      public:
        bool operator()(const value_type& __x, const value_type& __y) const {
          return comp(__x.first, __y.first);
        }
      };
    
    private:
    	//底层机制是RB-Tree
      typedef _Rb_tree<key_type, value_type, 
                      _Select1st<value_type>, key_compare, _Alloc> _Rep_type;
      _Rep_type _M_t;  // red-black tree representing multimap
    public:
      typedef typename _Rep_type::pointer pointer;
      typedef typename _Rep_type::const_pointer const_pointer;
      typedef typename _Rep_type::reference reference;
      typedef typename _Rep_type::const_reference const_reference;
      //map的迭代器不直接定义为const_iterator,而是分别定义iterator,const_iterator
      //是因为map的键值key不能被修改,因为必须遵守比较函数的排序规则,所以必须定义为const_iterator
      //而map的实值value可以被修改,则定义为iterator
      typedef typename _Rep_type::iterator iterator;
      typedef typename _Rep_type::const_iterator const_iterator; 
      typedef typename _Rep_type::reverse_iterator reverse_iterator;
      typedef typename _Rep_type::const_reverse_iterator const_reverse_iterator;
      typedef typename _Rep_type::size_type size_type;
      typedef typename _Rep_type::difference_type difference_type;
      typedef typename _Rep_type::allocator_type allocator_type;
    
    // allocation/deallocation
      // 注意:multimap只能使用RB-tree的insert-equal(),不能使用insert-unique() 
    
      /*
      构造函数
    		multimap();
    		explicit multimap (const key_compare& comp = key_compare(),
    					   const allocator_type& alloc = allocator_type());
    		
    		template <class InputIterator>
    		multimap (InputIterator first, InputIterator last,
    				const key_compare& comp = key_compare(),
    				const allocator_type& alloc = allocator_type());
    	
    		multimap (const multimap& x);
      */
    
      multimap() : _M_t(_Compare(), allocator_type()) { }
      explicit multimap(const _Compare& __comp,
                        const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { }
    
    #ifdef __STL_MEMBER_TEMPLATES  
      template <class _InputIterator>
      multimap(_InputIterator __first, _InputIterator __last)
        : _M_t(_Compare(), allocator_type())
        { _M_t.insert_equal(__first, __last); }
    
      template <class _InputIterator>
      multimap(_InputIterator __first, _InputIterator __last,
               const _Compare& __comp,
               const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_equal(__first, __last); }
    #else
      multimap(const value_type* __first, const value_type* __last)
        : _M_t(_Compare(), allocator_type())
        { _M_t.insert_equal(__first, __last); }
      multimap(const value_type* __first, const value_type* __last,
               const _Compare& __comp,
               const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_equal(__first, __last); }
    
      multimap(const_iterator __first, const_iterator __last)
        : _M_t(_Compare(), allocator_type())
        { _M_t.insert_equal(__first, __last); }
      multimap(const_iterator __first, const_iterator __last,
               const _Compare& __comp,
               const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_equal(__first, __last); }
    #endif /* __STL_MEMBER_TEMPLATES */
      //拷贝构造函数
      multimap(const multimap<_Key,_Tp,_Compare,_Alloc>& __x) : _M_t(__x._M_t) { }
      //这里提供了operator=,即可以通过=初始化对象
      multimap<_Key,_Tp,_Compare,_Alloc>&
      operator=(const multimap<_Key,_Tp,_Compare,_Alloc>& __x) {
        _M_t = __x._M_t;
        return *this; 
      }
    
      // accessors:
       //返回键值的比较函数,这里是调用RB-Tree的key_comp()
      key_compare key_comp() const { return _M_t.key_comp(); }
       //返回实值的比较函数
      //这里调用的是map嵌套类中定义的比较函数
      /*
    	  class value_compare
    		: public binary_function<value_type, value_type, bool> {
    	  friend class map<_Key,_Tp,_Compare,_Alloc>;
    	  protected :
    		_Compare comp;
    		value_compare(_Compare __c) : comp(__c) {}
    	  public:
    		bool operator()(const value_type& __x, const value_type& __y) const {
    		  return comp(__x.first, __y.first);//以键值调用比较函数
    		}
      */
      //实际上最终还是调用键值key的比较函数，即他们是调用同一个比较函数
      value_compare value_comp() const { return value_compare(_M_t.key_comp()); }
      allocator_type get_allocator() const { return _M_t.get_allocator(); }
    
      iterator begin() { return _M_t.begin(); }
      const_iterator begin() const { return _M_t.begin(); }
      iterator end() { return _M_t.end(); }
      const_iterator end() const { return _M_t.end(); }
      reverse_iterator rbegin() { return _M_t.rbegin(); }
      const_reverse_iterator rbegin() const { return _M_t.rbegin(); }
      reverse_iterator rend() { return _M_t.rend(); }
      const_reverse_iterator rend() const { return _M_t.rend(); }
      //判断容器multimap是否为空
      bool empty() const { return _M_t.empty(); }
      //返回容器multimap的大小
      size_type size() const { return _M_t.size(); }
      size_type max_size() const { return _M_t.max_size(); }
      //交换multimap对象的内容
      void swap(multimap<_Key,_Tp,_Compare,_Alloc>& __x) { _M_t.swap(__x._M_t); }
    
      // insert/erase
      /*
    	multimap只能使用RB-tree的insert-equal()
    	插入元素
    	iterator insert (const value_type& val);
    	
    	iterator insert (iterator position, const value_type& val);
    	
    	template <class InputIterator>
    	void insert (InputIterator first, InputIterator last);
      */
      //插入元素节点,调用RB-Tree的insert-equal();
      //插入元素的键值key允许重复
      iterator insert(const value_type& __x) { return _M_t.insert_equal(__x); }
      //在指定位置插入元素
      iterator insert(iterator __position, const value_type& __x) {
        return _M_t.insert_equal(__position, __x);
      }
    #ifdef __STL_MEMBER_TEMPLATES  
      //插入[first,last)元素
      template <class _InputIterator>
      void insert(_InputIterator __first, _InputIterator __last) {
        _M_t.insert_equal(__first, __last);
      }
    #else
      void insert(const value_type* __first, const value_type* __last) {
        _M_t.insert_equal(__first, __last);
      }
      void insert(const_iterator __first, const_iterator __last) {
        _M_t.insert_equal(__first, __last);
      }
    #endif /* __STL_MEMBER_TEMPLATES */
      /*
    	擦除元素
    	void erase (iterator position);
    
    	size_type erase (const key_type& k);
    	
        void erase (iterator first, iterator last);
      */
      //在指定位置擦除元素
      void erase(iterator __position) { _M_t.erase(__position); }
      //擦除指定键值的节点
      size_type erase(const key_type& __x) { return _M_t.erase(__x); }
      //擦除指定区间的节点
      void erase(iterator __first, iterator __last)
        { _M_t.erase(__first, __last); }
      //清空容器
      void clear() { _M_t.clear(); }
    
      // multimap operations:
    
      //查找指定键值的节点
      iterator find(const key_type& __x) { return _M_t.find(__x); }
      const_iterator find(const key_type& __x) const { return _M_t.find(__x); }
      //计算指定键值元素的个数
      size_type count(const key_type& __x) const { return _M_t.count(__x); }
       //Returns an iterator pointing to the first element in the container 
      //whose key is not considered to go before k (i.e., either it is equivalent or goes after).
      //this->first is greater than or equivalent to __x.
      iterator lower_bound(const key_type& __x) {return _M_t.lower_bound(__x); }
      const_iterator lower_bound(const key_type& __x) const {
        return _M_t.lower_bound(__x); 
      }
      //Returns an iterator pointing to the first element that is greater than key.
      iterator upper_bound(const key_type& __x) {return _M_t.upper_bound(__x); }
      const_iterator upper_bound(const key_type& __x) const {
        return _M_t.upper_bound(__x); 
      }
      //Returns the bounds of a range that includes all the elements in the container 
      //which have a key equivalent to k
      //Because the elements in a map container have unique keys, 
      //the range returned will contain a single element at most.
       pair<iterator,iterator> equal_range(const key_type& __x) {
        return _M_t.equal_range(__x);
      }
      pair<const_iterator,const_iterator> equal_range(const key_type& __x) const {
        return _M_t.equal_range(__x);
      }
    
    
      //以下是操作符重载
    #ifdef __STL_TEMPLATE_FRIENDS 
      template <class _K1, class _T1, class _C1, class _A1>
      friend bool operator== (const multimap<_K1, _T1, _C1, _A1>&,
                              const multimap<_K1, _T1, _C1, _A1>&);
      template <class _K1, class _T1, class _C1, class _A1>
      friend bool operator< (const multimap<_K1, _T1, _C1, _A1>&,
                             const multimap<_K1, _T1, _C1, _A1>&);
    #else /* __STL_TEMPLATE_FRIENDS */
      friend bool __STD_QUALIFIER
      operator== __STL_NULL_TMPL_ARGS (const multimap&, const multimap&);
      friend bool __STD_QUALIFIER
      operator< __STL_NULL_TMPL_ARGS (const multimap&, const multimap&);
    #endif /* __STL_TEMPLATE_FRIENDS */
    };
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator==(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return __x._M_t == __y._M_t;
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator<(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return __x._M_t < __y._M_t;
    }
    
    #ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator!=(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__x == __y);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator>(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return __y < __x;
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator<=(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__y < __x);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator>=(const multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__x < __y);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline void swap(multimap<_Key,_Tp,_Compare,_Alloc>& __x, 
                     multimap<_Key,_Tp,_Compare,_Alloc>& __y) {
      __x.swap(__y);
    }
    
    #endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */
    
    #if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
    #pragma reset woff 1174
    #pragma reset woff 1375
    #endif
    
    __STL_END_NAMESPACE
    
    #endif /* __SGI_STL_INTERNAL_MULTIMAP_H */
    
    // Local Variables:
    // mode:C++
    // End:

参考资料：

《STL源码剖析》侯捷

[map]: http://blog.csdn.net/chenhanzhun/article/details/39529425