STL源码 SET 解析

这个是阿里春招实习二面的时候面试官问的一个问题。

SET是STL中的标准容器，SET里面的元素会根据键值自动排序，它不像map那样拥有实值value和键值key的对应，set只有实值。SET的底层实现时RB-tree，当插入到RB-tree中后，其值不能再更改，因为更改就意味着可能不符合RB-tree的特性了，所以其迭代器set<T>::iterator是RB-tree的constrant iterator。由于SET底层是RB-tree，所以SET在插入等操作之后，迭代器不会失效，但删除元素的迭代器是个例外。

 G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_set.h 完整列表
 /*
  *
  * Copyright (c) 1994
  * Hewlett-Packard Company
  *
  * Permission to use, copy, modify, distribute and sell this software
  * and its documentation for any purpose is hereby granted without fee,
  * provided that the above copyright notice appear in all copies and
  * that both that copyright notice and this permission notice appear
  * in supporting documentation.  Hewlett-Packard Company makes no
  * representations about the suitability of this software for any
  * purpose.  It is provided "as is" without express or implied warranty.
  *
  *
  * Copyright (c) 1996,1997
  * Silicon Graphics Computer Systems, Inc.
  *
  * Permission to use, copy, modify, distribute and sell this software
  * and its documentation for any purpose is hereby granted without fee,
  * provided that the above copyright notice appear in all copies and
  * that both that copyright notice and this permission notice appear
  * in supporting documentation.  Silicon Graphics makes no
  * representations about the suitability of this software for any
  * purpose.  It is provided "as is" without express or implied warranty.
  */

 /* NOTE: This is an internal header file, included by other STL headers.
  *   You should not attempt to use it directly.
  */

 #ifndef __SGI_STL_INTERNAL_SET_H
 #define __SGI_STL_INTERNAL_SET_H

 __STL_BEGIN_NAMESPACE

 #if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
 #pragma set woff 1174
 #endif
 //less<Key>说明默认使用递增排序
 #ifndef __STL_LIMITED_DEFAULT_TEMPLATES
 template <class Key, class Compare = less<Key>, class Alloc = alloc>
 #else
 template <class Key, class Compare, class Alloc = alloc>
 #endif
 class set {
 public:
   // typedefs:

   //key_type和 value_type类型都是实值
   typedef Key key_type;
   typedef Key value_type;
   // 注意，以下 key_compare 和 value_compare 使用相同的比较函数
   typedef Compare key_compare;
   typedef Compare value_compare;
 private:
   /* 注意，identity 定义于 <stl_function.h>，参考第7章，其定义为：
     template <class T>
     struct identity : public unary_function<T, T> {
       const T& operator()(const T& x) const { return x; }
     };
   */
   // 以下，rb_tree<Key, Value, KeyOfValue, Compare, Alloc>
   typedef rb_tree<key_type, value_type,
                      identity<value_type>, key_compare, Alloc> rep_type;
   rep_type t;  // 底层采用红黑树
 public:
   typedef typename rep_type::const_pointer pointer;
   typedef typename rep_type::const_pointer const_pointer;
   typedef typename rep_type::const_reference reference;
   typedef typename rep_type::const_reference const_reference;
   //用的是RB-tree的 const_iterator。不允许修改其值，也不允许使用者在任意处插入元素
   typedef typename rep_type::const_iterator iterator;

   typedef typename rep_type::const_iterator const_iterator;
   typedef typename rep_type::const_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;

   // allocation/deallocation
   // 注意， set 一定使用 insert_unique() 而不使用 insert_equal()。
   // multiset 才使用 insert_equal()。
   set() : t(Compare()) {}
   explicit set(const Compare& comp) : t(comp) {}
 //初始化SET
 #ifdef __STL_MEMBER_TEMPLATES
   template <class InputIterator>
   set(InputIterator first, InputIterator last)
     : t(Compare()) { t.insert_unique(first, last); }

   template <class InputIterator>
   set(InputIterator first, InputIterator last, const Compare& comp)
     : t(comp) { t.insert_unique(first, last); }
 #else
   set(const value_type* first, const value_type* last)
     : t(Compare()) { t.insert_unique(first, last); }
   set(const value_type* first, const value_type* last, const Compare& comp)
     : t(comp) { t.insert_unique(first, last); }

   set(const_iterator first, const_iterator last)
     : t(Compare()) { t.insert_unique(first, last); }
   set(const_iterator first, const_iterator last, const Compare& comp)
     : t(comp) { t.insert_unique(first, last); }
 #endif /* __STL_MEMBER_TEMPLATES */

   set(const set<Key, Compare, Alloc>& x) : t(x.t) {}
   set<Key, Compare, Alloc>& operator=(const set<Key, Compare, Alloc>& x) {
     t = x.t;
     return *this;
   }

   //一下所有的SET操作，RB-tree都已经提供，SET只是调用而已

   // accessors:
   key_compare key_comp() const { return t.key_comp(); }
   // 以下注意，set 的value_comp() 实际上就是RB-tree 的key_comp()。
   value_compare value_comp() const { return t.key_comp(); }
   iterator begin() const { return t.begin(); }
   iterator end() const { return t.end(); }
   reverse_iterator rbegin() const { return t.rbegin(); }
   reverse_iterator rend() const { return t.rend(); }
   bool empty() const { return t.empty(); }
   size_type size() const { return t.size(); }
   size_type max_size() const { return t.max_size(); }
   void swap(set<Key, Compare, Alloc>& x) { t.swap(x.t); }

   // insert/erase
   typedef  pair<iterator, bool> pair_iterator_bool;
   pair<iterator,bool> insert(const value_type& x) {
     pair<typename rep_type::iterator, bool> p = t.insert_unique(x);
     return pair<iterator, bool>(p.first, p.second);
   }
   iterator insert(iterator position, const value_type& x) {
     typedef typename rep_type::iterator rep_iterator;
     return t.insert_unique((rep_iterator&)position, x);
   }
 #ifdef __STL_MEMBER_TEMPLATES
   template <class InputIterator>
   void insert(InputIterator first, InputIterator last) {
     t.insert_unique(first, last);
   }
 #else
   void insert(const_iterator first, const_iterator last) {
     t.insert_unique(first, last);
   }
   void insert(const value_type* first, const value_type* last) {
     t.insert_unique(first, last);
   }
 #endif /* __STL_MEMBER_TEMPLATES */
   void erase(iterator position) {
     typedef typename rep_type::iterator rep_iterator;
     t.erase((rep_iterator&)position);
   }
   size_type erase(const key_type& x) {
     return t.erase(x);
   }
   void erase(iterator first, iterator last) {
     typedef typename rep_type::iterator rep_iterator;
     t.erase((rep_iterator&)first, (rep_iterator&)last);
   }
   void clear() { t.clear(); }

   // set operations:
   //使用的是RB-tree的搜索函数，而不是STL的find，STL的find的只是
   //循序搜索，效率不如关联容器自己定义的效率高
   iterator find(const key_type& x) const { return t.find(x); }
   size_type count(const key_type& x) const { return t.count(x); }
   iterator lower_bound(const key_type& x) const {
     return t.lower_bound(x);
   }
   iterator upper_bound(const key_type& x) const {
     return t.upper_bound(x);
   }
   pair<iterator,iterator> equal_range(const key_type& x) const {
     return t.equal_range(x);
   }
   friend bool operator== __STL_NULL_TMPL_ARGS (const set&, const set&);
   friend bool operator< __STL_NULL_TMPL_ARGS (const set&, const set&);
 };

 template <class Key, class Compare, class Alloc>
 inline bool operator==(const set<Key, Compare, Alloc>& x,
                        const set<Key, Compare, Alloc>& y) {
   return x.t == y.t;
 }

 template <class Key, class Compare, class Alloc>
 inline bool operator<(const set<Key, Compare, Alloc>& x,
                       const set<Key, Compare, Alloc>& y) {
   return x.t < y.t;
 }

 #ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER

 template <class Key, class Compare, class Alloc>
 inline void swap(set<Key, Compare, Alloc>& x,
                  set<Key, 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
 #endif

 __STL_END_NAMESPACE

 #endif /* __SGI_STL_INTERNAL_SET_H */

 // Local Variables:
 // mode:C++
 // End: