STL源码剖析——关联容器之map

悠悠 2022-08-12 12:00 127阅读 0赞

## 前言 ##

在SGI STL中的容器map，底层实现机制是RB-Tree，是因为map的操作RB-Tree都能实现，有关RB-Tree的剖析请看《[STL源码剖析——RB-Tree][STL_RB-Tree][(红黑树)][STL_RB-Tree]》。在map容器键值key和实值value是不相同的，键值key和实值value的比较函数也是不同的。在容器里面的元素是根据元素的键值自动排序的，不能修改map容器的键值，但是可以修改容器的实值。map的所有节点元素都是pair,pair有两个成员变量first，second；第一个first是键值key,第二个second是实值value；有关pair的介绍见前文《[stl\_pair.h学习][stl_pair.h]》剖析。本文的源码出自SGI STL中的<stl\_map.h>文件。

## map容器源码剖析 ##

在源码剖析的时候，会针对一些函数给出例子，例子包含在剖析文件里面。

#ifndef __SGI_STL_INTERNAL_MAP_H
    #define __SGI_STL_INTERNAL_MAP_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
    /*
    	map的所有节点元素都是pair,pair有两个成员变量first，second
    	第一个first是键值key,第二个second是实值value
    	有关pair的定义见前文<stl_pair.h>剖析
    */
    
    //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：map键值和实值是分开的，map的键值key是唯一的，实值value可以重复
    //不能通过迭代器修改map的键值key,其迭代器类型是定义为RB-Tree的const_iterator
    //但是可以通过迭代器修改map的实值value
    
    // Forward declarations of operators == and <, needed for friend declarations.
    template <class _Key, class _Tp, 
              class _Compare __STL_DEPENDENT_DEFAULT_TMPL(less<_Key>),
              class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp) >
    class map;
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator==(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const map<_Key,_Tp,_Compare,_Alloc>& __y);
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator<(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const map<_Key,_Tp,_Compare,_Alloc>& __y);
    
    //map定义
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    class map {
    public:
    
    // requirements:
    
      __STL_CLASS_REQUIRES(_Tp, _Assignable);
      __STL_CLASS_BINARY_FUNCTION_CHECK(_Compare, bool, _Key, _Key);
    
    // typedefs:
    
      typedef _Key                  key_type;//键值key类型
      typedef _Tp                   data_type;//数据(实值)value类型
      typedef _Tp                   mapped_type;
      typedef pair<const _Key, _Tp> value_type;//元素型别,包含(键值/实值),const保证键值key不被修改
      typedef _Compare              key_compare;//键值key比较函数
        
      //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 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
        }
      };
    
    private:
    	//底层机制是RB-Tree
    	//以map类型（一个pair）的第一个类型作为TB-tree的键值类型.  
    	//所以在RB-tree中，键值key不能修改
      typedef _Rb_tree<key_type, value_type, 
                       _Select1st<value_type>, key_compare, _Alloc> _Rep_type;
      _Rep_type _M_t;  // red-black tree representing map
    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,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
      // map只能使用RB-tree的insert-unique(),不能使用insert-equal() 
      //因为必须保证键值唯一
      /*
    				构造函数
    	map();
    	explicit map (const key_compare& comp = key_compare(),
                  const allocator_type& alloc = allocator_type());
    	
    	template <class InputIterator>
    	map (InputIterator first, InputIterator last,
           const key_compare& comp = key_compare(),
           const allocator_type& alloc = allocator_type());
    	
    	map (const map& x);
      */
      /*
    	example:
    	#include <iostream>
    	#include <map>
    
    	bool fncomp (char lhs, char rhs) {return lhs<rhs;}
    
    	struct classcomp {
    	  bool operator() (const char& lhs, const char& rhs) const
    	  {return lhs<rhs;}
    	};
    
    	int main ()
    	{
    	  std::map<char,int> first;
    
    	  first['a']=10;
    	  first['b']=30;
    	  first['c']=50;
    	  first['d']=70;
    
    	  std::map<char,int> second (first.begin(),first.end());
    
    	  std::map<char,int> third (second);
    
    	  std::map<char,int,classcomp> fourth;                 // class as Compare
    
    	  bool(*fn_pt)(char,char) = fncomp;
    	  std::map<char,int,bool(*)(char,char)> fifth (fn_pt); // function pointer as Compare
    
    	  return 0;
    	}
      */
    
      map() : _M_t(_Compare(), allocator_type()) {}
      explicit map(const _Compare& __comp,
                   const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) {}
    
    #ifdef __STL_MEMBER_TEMPLATES
      template <class _InputIterator>
      map(_InputIterator __first, _InputIterator __last)
        : _M_t(_Compare(), allocator_type())
        { _M_t.insert_unique(__first, __last); }
    
      template <class _InputIterator>
      map(_InputIterator __first, _InputIterator __last, const _Compare& __comp,
          const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_unique(__first, __last); }
    #else
      map(const value_type* __first, const value_type* __last)
        : _M_t(_Compare(), allocator_type())
        { _M_t.insert_unique(__first, __last); }
    
      map(const value_type* __first,
          const value_type* __last, const _Compare& __comp,
          const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_unique(__first, __last); }
    
      map(const_iterator __first, const_iterator __last)
        : _M_t(_Compare(), allocator_type()) 
        { _M_t.insert_unique(__first, __last); }
    
      map(const_iterator __first, const_iterator __last, const _Compare& __comp,
          const allocator_type& __a = allocator_type())
        : _M_t(__comp, __a) { _M_t.insert_unique(__first, __last); }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
      //拷贝构造函数
      map(const map<_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
      map<_Key,_Tp,_Compare,_Alloc>&
      operator=(const map<_Key, _Tp, _Compare, _Alloc>& __x)
      {
        _M_t = __x._M_t;
        return *this; 
      }
    
      // accessors:
    
      //以下调用RB-Tree的操作
      //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()); }
      //获得分配器的类型
      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(); }
      bool empty() const { return _M_t.empty(); }
      size_type size() const { return _M_t.size(); }
      size_type max_size() const { return _M_t.max_size(); }
      //重载operator[],返回是实值value(即pair.second)的引用
      //注意:若你原先没有定义map对象,即你访问的键值key不存在,则会自动新建一个map对象
      //键值key为你访问的键值key,实值value为空,看下面的例子就明白了
        _Tp& operator[](const key_type& __k) {
        iterator __i = lower_bound(__k);
        // __i->first is greater than or equivalent to __k.
        if (__i == end() || key_comp()(__k, (*__i).first))
          __i = insert(__i, value_type(__k, _Tp()));
        return (*__i).second;
    	//其实简单的方式是直接返回
    	//return (*((insert(value_type(k, T()))).first)).second;
      }
    	/*
    	example:
    	#include <iostream>
    	#include <map>
    	#include <string>
    
    	int main ()
    	{
    	  std::map<char,std::string> mymap;
    
    	  mymap['a']="an element";
    	  mymap['b']="another element";
    	  mymap['c']=mymap['b'];
    
    	  std::cout << "mymap['a'] is " << mymap['a'] << '\n';
    	  std::cout << "mymap['b'] is " << mymap['b'] << '\n';
    	  std::cout << "mymap['c'] is " << mymap['c'] << '\n';
    	  std::cout << "mymap['d'] is " << mymap['d'] << '\n';
    
    	  std::cout << "mymap now contains " << mymap.size() << " elements.\n";
    
    	  return 0;
    	}
    	Ouput:
    	mymap['a'] is an element
    	mymap['b'] is another element
    	mymap['c'] is another element
    	mymap['d'] is
    	mymap now contains 4 elements.
      */
    	//交换map对象的内容
      void swap(map<_Key,_Tp,_Compare,_Alloc>& __x) { _M_t.swap(__x._M_t); }
    
      // insert/erase
      /*
    	插入元素
    	single element (1):	
    	pair<iterator,bool> insert (const value_type& val);
    
    	with hint (2):
    	iterator insert (iterator position, const value_type& val);
    
    	range (3):	
    	template <class InputIterator>
    	void insert (InputIterator first, InputIterator last);
      */
    
      //插入元素节点,调用RB-Tree的insert_unique(__x);
      //不能插入相同键值的元素
      pair<iterator,bool> insert(const value_type& __x) 
        { return _M_t.insert_unique(__x); }
      //在指定位置插入元素，但是会先遍历该集合,判断是否存在相同元素
      //若不存在才在指定位置插入该元素
      iterator insert(iterator position, const value_type& __x)
        { return _M_t.insert_unique(position, __x); }
    #ifdef __STL_MEMBER_TEMPLATES
      template <class _InputIterator>
      void insert(_InputIterator __first, _InputIterator __last) {
        _M_t.insert_unique(__first, __last);
      }
    #else
      void insert(const value_type* __first, const value_type* __last) {
        _M_t.insert_unique(__first, __last);
      }
      void insert(const_iterator __first, const_iterator __last) {
        _M_t.insert_unique(__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map
      void clear() { _M_t.clear(); }
    
      // map 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.find(__x) == _M_t.end() ? 0 : 1; 
      }
    
      /*
    	Example:
    	#include <iostream>
    	#include <map>
    
    	int main ()
    	{
    	  std::map<char,int> mymap;
    	  std::map<char,int>::iterator itlow,itup;
    
    	  mymap['a']=20;
    	  mymap['b']=40;
    	  mymap['c']=60;
    	  mymap['d']=80;
    	  mymap['e']=100;
    
    	  itlow=mymap.lower_bound ('b');  // itlow points to b
    	  itup=mymap.upper_bound ('d');   // itup points to e (not d!)
    
    	  mymap.erase(itlow,itup);        // erases [itlow,itup)
    
    	  // print content:
    	  for (std::map<char,int>::iterator it=mymap.begin(); it!=mymap.end(); ++it)
    		std::cout << it->first << " => " << it->second << '\n';
    
    	  return 0;
    	}
    	Output:
    	a => 20
    	e => 100
      */
      //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);
      }
      /*
      Example:
    	#include <iostream>
    	#include <map>
    
    	int main ()
    	{
    	  std::map<char,int> mymap;
    
    	  mymap['a']=10;
    	  mymap['b']=20;
    	  mymap['c']=30;
    
    	  std::pair<std::map<char,int>::iterator,std::map<char,int>::iterator> ret;
    	  ret = mymap.equal_range('b');
    
    	  std::cout << "lower bound points to: ";
    	  std::cout << ret.first->first << " => " << ret.first->second << '\n';
    
    	  std::cout << "upper bound points to: ";
    	  std::cout << ret.second->first << " => " << ret.second->second << '\n';
    
    	  return 0;
    	}
    	Output:
    		lower bound points to: 'b' => 20
    		upper bound points to: 'c' => 30
      */
    
    //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 map<_K1, _T1, _C1, _A1>&,
                              const map<_K1, _T1, _C1, _A1>&);
      template <class _K1, class _T1, class _C1, class _A1>
      friend bool operator< (const map<_K1, _T1, _C1, _A1>&,
                             const map<_K1, _T1, _C1, _A1>&);
    #else /* __STL_TEMPLATE_FRIENDS */
      friend bool __STD_QUALIFIER
      operator== __STL_NULL_TMPL_ARGS (const map&, const map&);
      friend bool __STD_QUALIFIER
      operator< __STL_NULL_TMPL_ARGS (const map&, const map&);
    #endif /* __STL_TEMPLATE_FRIENDS */
    };
    
    //比较两个map的内容
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator==(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const map<_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 map<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const map<_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 map<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const map<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__x == __y);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator>(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                          const map<_Key,_Tp,_Compare,_Alloc>& __y) {
      return __y < __x;
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator<=(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const map<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__y < __x);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline bool operator>=(const map<_Key,_Tp,_Compare,_Alloc>& __x, 
                           const map<_Key,_Tp,_Compare,_Alloc>& __y) {
      return !(__x < __y);
    }
    
    template <class _Key, class _Tp, class _Compare, class _Alloc>
    inline void swap(map<_Key,_Tp,_Compare,_Alloc>& __x, 
                     map<_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_MAP_H */
    
    // Local Variables:
    // mode:C++
    // End:

参考资料：

《STL源码剖析》侯捷

《[STL源码剖析-- stl\_map.h][STL_-- stl_map.h]》

[STL_RB-Tree]: http://blog.csdn.net/chenhanzhun/article/details/39523519
[stl_pair.h]: http://blog.csdn.net/chenhanzhun/article/details/39526719
[STL_-- stl_map.h]: http://blog.csdn.net/mdl13412/article/details/6655581