《STL源码剖析》---stl_list.h阅读笔记

STL中链表list是一个常用的容器。list在内存中是不连续的双向链表，且是环形的。要了解链表细节是如何操作的话，阅读STL关于链表的代码是最好的方法。

G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_list.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_LIST_H
#define __SGI_STL_INTERNAL_LIST_H

__STL_BEGIN_NAMESPACE

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma set woff 1174
#endif

// List结点结构，List是双向的
template 
struct __list_node {
  typedef void* void_pointer;
  void_pointer next;  // 其实可以设为 __list_node*
  void_pointer prev;
  T data;
};


//list是一个双向链表，其迭代器可以向前移、向后移
//因此迭代器类型为bidirectional_iterator_tag
template
struct __list_iterator { // 没有继承 std::iterator
  typedef __list_iterator             iterator;
  typedef __list_iterator const_iterator;
  typedef __list_iterator           self;

  // 没有继承 std::iterator，自己定义迭代器5个类别
  typedef bidirectional_iterator_tag iterator_category;	 // (1)
  typedef T value_type; 			// (2)
  typedef Ptr pointer; 			// (3)
  typedef Ref reference; 			// (4)
  typedef __list_node* link_type;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type; // (5)

  link_type node;  // 原生态指针，指向实际的List结点

  //迭代器的构造函数
  __list_iterator(link_type x) : node(x) {}
  __list_iterator() {}
  __list_iterator(const iterator& x) : node(x.node) {}

  // 迭代器需要重载的运算符，为了支持标准算法STL
  bool operator==(const self& x) const { return node == x.node; }
  bool operator!=(const self& x) const { return node != x.node; }
  
  //对迭代器dereference，取的是迭代器所维护的结点的值
  reference operator*() const { return (*node).data; }	

#ifndef __SGI_STL_NO_ARROW_OPERATOR //如果支持->操作
  /*
  返回的是所维护结点的地址（可以理解为指针）。
  这时，可以把迭代器当作原生态指针来调用结点的函数
  */
  pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */


  //迭代器前进、后退的支持
  self& operator++() { 
    node = (link_type)((*node).next);  	
    return *this;
  }
  self operator++(int) { 
    self tmp = *this;
    ++*this;
    return tmp;
  }
  
  self& operator--() { 
    node = (link_type)((*node).prev); 
    return *this;
  }
  self operator--(int) { 
    self tmp = *this;
    --*this;
    return tmp;
  }
};
//如果编译器不支持partial specialization偏特性化
#ifndef __STL_CLASS_PARTIAL_SPECIALIZATION
template 
inline bidirectional_iterator_tag
iterator_category(const __list_iterator&) {
  return bidirectional_iterator_tag();
}

template 
inline T*
value_type(const __list_iterator&) {
  return 0;
}

template 
inline ptrdiff_t*
distance_type(const __list_iterator&) {
  return 0;
}
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

//下面是List的定义
template  // 默认为 alloc 为配置器
class list {
protected:
  typedef void* void_pointer;
  typedef __list_node list_node;
  // List的空间配置器，每次只配置一个结点
  typedef simple_alloc list_node_allocator;
public:      
  typedef T value_type;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  typedef list_node* link_type;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;

public:
/*
当开发者定义一个迭代器时list::iterator，首先调用的是
 __list_iterator的构造函数。如果有初始值，便会
 因此设定迭代器和容器的联结关系
*/
  typedef __list_iterator             iterator;
  typedef __list_iterator const_iterator;

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
  typedef reverse_iterator const_reverse_iterator;
  typedef reverse_iterator reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
  typedef reverse_bidirectional_iterator
  const_reverse_iterator;
  typedef reverse_bidirectional_iterator
  reverse_iterator; 
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

protected:
  // 配置一个结点（未初始化），返回其指针
  link_type get_node() { return list_node_allocator::allocate(); }
  // 释放一个结点
  void put_node(link_type p) { list_node_allocator::deallocate(p); }

  // 配置一个结点，并用x初始化
  link_type create_node(const T& x) {
    link_type p = get_node();
    __STL_TRY {
      construct(&p->data, x);	// 全局函数
    }
    __STL_UNWIND(put_node(p));
    return p;
  }
  // 销毁一个结点
  void destroy_node(link_type p) {
    destroy(&p->data); 		//全局函数
    put_node(p);
  }

protected:
	//初始化一个空链表，首尾相连
  void empty_initialize() { 
    node = get_node();	
    node->next = node;	
    node->prev = node;
  }
  //初始化长为n的链表，值都为value
  void fill_initialize(size_type n, const T& value) {
    empty_initialize();
    __STL_TRY {
      insert(begin(), n, value);
    }
    __STL_UNWIND(clear(); put_node(node));
  }

#ifdef __STL_MEMBER_TEMPLATES
  //以迭代器的区间初始化一个链表
  template 
  void range_initialize(InputIterator first, InputIterator last) {
    empty_initialize();
    __STL_TRY {
      insert(begin(), first, last);
    }
	//commit or rollback
    __STL_UNWIND(clear(); put_node(node));
  }
#else  /* __STL_MEMBER_TEMPLATES */
  void range_initialize(const T* first, const T* last) {
    empty_initialize();
    __STL_TRY {
      insert(begin(), first, last);
    }
    __STL_UNWIND(clear(); put_node(node));
  }
  void range_initialize(const_iterator first, const_iterator last) {
    empty_initialize();
    __STL_TRY {
      insert(begin(), first, last);
    }
    __STL_UNWIND(clear(); put_node(node));
  }
#endif /* __STL_MEMBER_TEMPLATES */

protected:
  /*
  List只维护这一个结点，它指向List未结点的下一个位置，即头结点，因为List是一个
  环形的双向链表。
  该结点是空结点，next指向头结点。
  */
  link_type node; // 可以认为它是哨兵结点（在算法导论中有讲哨兵结点）

public:
  list() { empty_initialize(); }  // 默认构造函数，空链表。
  //指向头结点的迭代器
  iterator begin() { return (link_type)((*node).next); }
  const_iterator begin() const { return (link_type)((*node).next); }

  //指向尾结点下一个位置的迭代器，所以返回node
  iterator end() { return node; }	
    const_iterator end() const { return node; }
  reverse_iterator rbegin() { return reverse_iterator(end()); }
  const_reverse_iterator rbegin() const { 
    return const_reverse_iterator(end()); 
  }
  reverse_iterator rend() { return reverse_iterator(begin()); }
  const_reverse_iterator rend() const { 
    return const_reverse_iterator(begin());
  } 
  //链表只有node结点时为空链表
  bool empty() const { return node->next == node; }
  size_type size() const {
    size_type result = 0;
    distance(begin(), end(), result);  // 在定义，result是引用传递
    return result;
  }
  //链表最大容量。没什么意义吧？
  size_type max_size() const { return size_type(-1); }
  // 取链表头结点的内容
  reference front() { return *begin(); }  
  const_reference front() const { return *begin(); }
  // 取链表尾结点的内容
  reference back() { return *(--end()); } 
  const_reference back() const { return *(--end()); }
  //交换两个链表
  void swap(list& x) { __STD::swap(node, x.node); }

  // 在迭代器 position 所指位置前插入一个结点，其值为x。
  //在函数中 tmp为指针，返回的却是迭代器
  iterator insert(iterator position, const T& x) {
    link_type tmp = create_node(x); // 生成结点并用x初始化
    // 调整指针
    tmp->next = position.node;
    tmp->prev = position.node->prev;
	//prev和next指针都是void*，所以需要指针类型转换
    (link_type(position.node->prev))->next = tmp;
    position.node->prev = tmp;
    return tmp;
  }
  //在迭代器 position 所指位置前插入一个结点，其值为T的默认值，这也说明List的元素要有默认构造函数
  iterator insert(iterator position) { return insert(position, T()); }

  //在position所指位置前插入多个元素
#ifdef __STL_MEMBER_TEMPLATES
  template 
  void insert(iterator position, InputIterator first, InputIterator last);
#else /* __STL_MEMBER_TEMPLATES */
  void insert(iterator position, const T* first, const T* last);
  void insert(iterator position,
              const_iterator first, const_iterator last);
#endif /* __STL_MEMBER_TEMPLATES */
  void insert(iterator pos, size_type n, const T& x);
  void insert(iterator pos, int n, const T& x) {
    insert(pos, (size_type)n, x);
  }
  void insert(iterator pos, long n, const T& x) {
    insert(pos, (size_type)n, x);
  }

  // 在头结点前插入元素
  void push_front(const T& x) { insert(begin(), x); }
  // 在尾结点后插入元素
  void push_back(const T& x) { insert(end(), x); }

  // 移除迭代器 position 所指结点
  iterator erase(iterator position) {
    link_type next_node = link_type(position.node->next);
    link_type prev_node = link_type(position.node->prev);
    prev_node->next = next_node;
    next_node->prev = prev_node;
    destroy_node(position.node);
    return iterator(next_node);
  }
  iterator erase(iterator first, iterator last);
  void resize(size_type new_size, const T& x);
  void resize(size_type new_size) { resize(new_size, T()); }
  void clear();

  // 移除头结点
  void pop_front() { erase(begin()); }
  // 移除尾结点
  void pop_back() { 
    iterator tmp = end();
    erase(--tmp);
  }
  //几个构造函数
  list(size_type n, const T& value) { fill_initialize(n, value); }
  list(int n, const T& value) { fill_initialize(n, value); }
  list(long n, const T& value) { fill_initialize(n, value); }
  explicit list(size_type n) { fill_initialize(n, T()); }

 //用迭代器区间初始化List
#ifdef __STL_MEMBER_TEMPLATES
  template 
  list(InputIterator first, InputIterator last) {
    range_initialize(first, last);
  }

#else /* __STL_MEMBER_TEMPLATES */
  list(const T* first, const T* last) { range_initialize(first, last); }
  list(const_iterator first, const_iterator last) {
    range_initialize(first, last);
  }
#endif /* __STL_MEMBER_TEMPLATES */
  //用一个List初始化
  list(const list& x) {
    range_initialize(x.begin(), x.end());
  }
  ~list() {
    clear();//清除所有结点，哨兵结点除外
    put_node(node);//释放唯一的一个结点
  }
  list& operator=(const list& x);

protected:
  // 将[first,last) 內的所有元素搬移到position 前，不包括last元素。
  void transfer(iterator position, iterator first, iterator last) {
    if (position != last) {
		/*
		要把[first,last)在原有链表去除，然后安接到position前
		(1)-(7)步对应后面的图
		*/
      (*(link_type((*last.node).prev))).next = position.node;	// (1)
      (*(link_type((*first.node).prev))).next = last.node;		// (2)
      (*(link_type((*position.node).prev))).next = first.node;  	// (3)
      link_type tmp = link_type((*position.node).prev);			// (4)
      (*position.node).prev = (*last.node).prev;				// (5)
      (*last.node).prev = (*first.node).prev; 					// (6)
      (*first.node).prev = tmp;								// (7)
    }
  }

public:
  // 將 x 链表插入到 position 所指位置之前。x 不是 *this。
  void splice(iterator position, list& x) {
    if (!x.empty()) 
      transfer(position, x.begin(), x.end());
  }
  // 將 i 所指元素插入到 position 所指位置之前。position 和i 可在同一个list。
  void splice(iterator position, list&, iterator i) {
    iterator j = i;
    ++j;
    if (position == i || position == j) return;
    transfer(position, i, j);
  }
  // 將 [first,last) 內的所有元素插入到 position 所指位置之前。
  // position 和[first,last)可指在同一个list，
  // 但position不能位于[first,last)之內。
  void splice(iterator position, list&, iterator first, iterator last)  {
    if (first != last) 
      transfer(position, first, last);
  }
  void remove(const T& value);
  void unique();
  void merge(list& x);
  void reverse();
  void sort();

#ifdef __STL_MEMBER_TEMPLATES
  template  void remove_if(Predicate);
  template  void unique(BinaryPredicate);
  template  void merge(list&, StrictWeakOrdering);
  template  void sort(StrictWeakOrdering);
#endif /* __STL_MEMBER_TEMPLATES */

  friend bool operator== __STL_NULL_TMPL_ARGS (const list& x, const list& y);
};

//判断2个链表是否相同
template 
inline bool operator==(const list& x, const list& y) {
  typedef typename list::link_type link_type;
  link_type e1 = x.node;
  link_type e2 = y.node;
  link_type n1 = (link_type) e1->next;
  link_type n2 = (link_type) e2->next;
  for ( ; n1 != e1 && n2 != e2 ;
          n1 = (link_type) n1->next, n2 = (link_type) n2->next)
    if (n1->data != n2->data)
      return false;
  return n1 == e1 && n2 == e2;
}

//lexicographical_compare是STL算法
template 
inline bool operator<(const list& x, const list& y) {
  return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER

template 
//交换两个链表
inline void swap(list& x, list& y) {
  x.swap(y);
}

#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

#ifdef __STL_MEMBER_TEMPLATES
//在position之前插入迭代器区间的元素
template  template 
void list::insert(iterator position,
                            InputIterator first, InputIterator last) {
  for ( ; first != last; ++first)
    insert(position, *first);
}

#else /* __STL_MEMBER_TEMPLATES */

template 
void list::insert(iterator position, const T* first, const T* last) {
  for ( ; first != last; ++first)
    insert(position, *first);
}

template 
void list::insert(iterator position,
                            const_iterator first, const_iterator last) {
  for ( ; first != last; ++first)
    insert(position, *first);
}

#endif /* __STL_MEMBER_TEMPLATES */

//在position位置之前插入n个元素x
template 
void list::insert(iterator position, size_type n, const T& x) {
  for ( ; n > 0; --n)
    insert(position, x);
}
//擦除两个迭代器区间之间的元素
template 
list::iterator list::erase(iterator first, iterator last) {
  while (first != last) erase(first++);
  return last;
}
/*
重新调整链表大小为 new_size
如果new_size大于原来的链表，则在链表末尾插入x
如果new_size小于原来的链表，则在末尾直接擦除多余的元素
*/
template 
void list::resize(size_type new_size, const T& x)
{
  iterator i = begin();
  size_type len = 0;
  for ( ; i != end() && len < new_size; ++i, ++len)
    ;
  if (len == new_size)
    erase(i, end());
  else                          // i == end()
    insert(end(), new_size - len, x);
}

// 清除所有结点，（哨兵结点除外）
template  
void list::clear()
{
  link_type cur = (link_type) node->next; // begin()
  while (cur != node) {	
    link_type tmp = cur;
    cur = (link_type) cur->next;
    destroy_node(tmp); 	
  }
  // 恢复哨兵结点，链表此时为空链表
  node->next = node;
  node->prev = node;
}
//重载赋值=操作符
template 
list& list::operator=(const list& x) {
  if (this != &x) {//防止自身赋值
    iterator first1 = begin();
    iterator last1 = end();
    const_iterator first2 = x.begin();
    const_iterator last2 = x.end();
	//通过更改结点的值来赋值
    while (first1 != last1 && first2 != last2) *first1++ = *first2++;
	/*
	如果x链表小于this链表，擦除多余的，否则在this后面插入
	*/
    if (first2 == last2)
      erase(first1, last1);
    else
      insert(last1, first2, last2);
  }
  return *this;
}

// 将数值为value的结点移除
template 
void list::remove(const T& value) {
  iterator first = begin();
  iterator last = end();
  while (first != last) {	// 巡訪每一個節點
    iterator next = first;
    ++next;
    if (*first == value) erase(first); 	// 找到就移除
    first = next;
  }
}

// 移除数值相同的连续元素
template 
void list::unique() {
  iterator first = begin();
  iterator last = end();
  if (first == last) return;
  iterator next = first;
  while (++next != last) {
    if (*first == *next)//如果数值相同，则移除后面的那个
      erase(next);
    else
      first = next;
    next = first;
  }
}

//将x合并到*this上面。两个链表都要先经过递增排序。相当于合并排序的最后一步
template 
void list::merge(list& x) {
  iterator first1 = begin();
  iterator last1 = end();
  iterator first2 = x.begin();
  iterator last2 = x.end();

  //注意：此时已经假设两个链表都已经非递减排序好了
  while (first1 != last1 && first2 != last2)
    if (*first2 < *first1) {
      iterator next = first2;
      transfer(first1, first2, ++next);
      first2 = next;
    }
    else
      ++first1;
  if (first2 != last2) transfer(last1, first2, last2);
}

// 将 *this 的內容逆向重置
template 
void list::reverse() {

	//如果链表是空，或者只有一个元素，就不做任何处理
	//不是用size()==0或size()==1来判断，因为这样比较慢
  if (node->next == node || link_type(node->next)->next == node) return;
  iterator first = begin();
  ++first;
  while (first != end()) {
    iterator old = first;
    ++first;
    transfer(begin(), old, first);
  }
}    

/*
STL的sort算法只能接受迭代器类型为RamdonAccessIterator的容器，所以list无法
使用，故自己重写排序算法。这里使用的是快速排序。具体可以参考这里：http://blog.csdn.net/zhizichina/article/details/7538974
*/
template 
void list::sort() {
  
  if (node->next == node || link_type(node->next)->next == node) return;

  // carry作为tmp
  list carry;
  list counter[64];
  int fill = 0;
  while (!empty()) {
    carry.splice(carry.begin(), *this, begin());
    int i = 0;
    while(i < fill && !counter[i].empty()) {
      counter[i].merge(carry);
      carry.swap(counter[i++]);
    }
    carry.swap(counter[i]);         
    if (i == fill) ++fill;
  } 

  for (int i = 1; i < fill; ++i) 
     counter[i].merge(counter[i-1]);
  swap(counter[fill-1]);
}

#ifdef __STL_MEMBER_TEMPLATES
/*
pred是一个函数，如果容器内的元素经过pred函数判断为真，则移除
*/
template  template 
void list::remove_if(Predicate pred) {
  iterator first = begin();
  iterator last = end();
  while (first != last) {
    iterator next = first;
    ++next;
    if (pred(*first)) erase(first);
    first = next;
  }
}
/*
根据函数binary_pred来判断是否移除两个相邻的结点
*/
template  template 
void list::unique(BinaryPredicate binary_pred) {
  iterator first = begin();
  iterator last = end();
  if (first == last) return;
  iterator next = first;
  while (++next != last) {
    if (binary_pred(*first, *next))
      erase(next);
    else
      first = next;
    next = first;
  }
}
/*
假设两个链表均已经有序，用comp函数来判断如何合并两个链表
*/
template  template 
void list::merge(list& x, StrictWeakOrdering comp) {
  iterator first1 = begin();
  iterator last1 = end();
  iterator first2 = x.begin();
  iterator last2 = x.end();
  while (first1 != last1 && first2 != last2)
    if (comp(*first2, *first1)) {
      iterator next = first2;
      transfer(first1, first2, ++next);
      first2 = next;
    }
    else
      ++first1;
  if (first2 != last2) transfer(last1, first2, last2);
}
/*
用函数comp来判断如何排序链表
*/
template  template 
void list::sort(StrictWeakOrdering comp) {
  if (node->next == node || link_type(node->next)->next == node) return;
  list carry;
  list counter[64];
  int fill = 0;
  while (!empty()) {
    carry.splice(carry.begin(), *this, begin());
    int i = 0;
    while(i < fill && !counter[i].empty()) {
      counter[i].merge(carry, comp);
      carry.swap(counter[i++]);
    }
    carry.swap(counter[i]);         
    if (i == fill) ++fill;
  } 

  for (int i = 1; i < fill; ++i) counter[i].merge(counter[i-1], comp);
  swap(counter[fill-1]);
}

#endif /* __STL_MEMBER_TEMPLATES */

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma reset woff 1174
#endif

__STL_END_NAMESPACE 

#endif /* __SGI_STL_INTERNAL_LIST_H */

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// mode:C++
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