C++ STL源码学习(list篇）

///STL list为双向循环链表

struct _List_node_base {
_List_node_base* _M_next;
_List_node_base* _M_prev;
};

template <class _Tp>
struct _List_node : public _List_node_base {
_Tp _M_data;
};

struct _List_iterator_base {
typedef size_t                     size_type;
typedef ptrdiff_t                  difference_type;
typedef bidirectional_iterator_tag iterator_category;   ///迭代器为双向迭代器

_List_node_base* _M_node;   ///迭代器使用_List_node_base*标志其指向

_List_iterator_base(_List_node_base* __x) : _M_node(__x) {}
_List_iterator_base() {}

void _M_incr() { _M_node = _M_node->_M_next; }
void _M_decr() { _M_node = _M_node->_M_prev; }

bool operator==(const _List_iterator_base& __x) const {
return _M_node == __x._M_node;
}
bool operator!=(const _List_iterator_base& __x) const {
return _M_node != __x._M_node;
}
};

template<class _Tp, class _Ref, class _Ptr>
struct _List_iterator : public _List_iterator_base {
typedef _List_iterator<_Tp,_Tp&,_Tp*>             iterator;
typedef _List_iterator<_Tp,const _Tp&,const _Tp*> const_iterator;
typedef _List_iterator<_Tp,_Ref,_Ptr>             _Self;

typedef _Tp value_type;
typedef _Ptr pointer;
typedef _Ref reference;
typedef _List_node<_Tp> _Node;   ///实际指向的类型

_List_iterator(_Node* __x) : _List_iterator_base(__x) {}
_List_iterator() {}
_List_iterator(const iterator& __x) : _List_iterator_base(__x._M_node) {}

reference operator*() const { ///该函数虽然可能修改结点的值,但因迭代器对象只保存
///指向结点的指针,因此仍然声明为const
return ((_Node*) _M_node)->_M_data;
}

pointer operator->() const { return &(operator*()); }

_Self& operator++() {
this->_M_incr();
return *this;
}
_Self operator++(int) {
_Self __tmp = *this;
this->_M_incr();
return __tmp;
}
_Self& operator--() {
this->_M_decr();
return *this;
}
_Self operator--(int) {
_Self __tmp = *this;
this->_M_decr();
return __tmp;
}
};

inline bidirectional_iterator_tag
iterator_category(const _List_iterator_base&)
{
return bidirectional_iterator_tag();
}

template <class _Tp, class _Ref, class _Ptr>
inline _Tp*
value_type(const _List_iterator<_Tp, _Ref, _Ptr>&)
{
return 0;
}

inline ptrdiff_t*
distance_type(const _List_iterator_base&)
{
return 0;
}

template <class _Tp, class _Alloc>
class _List_base
{
public:
typedef _Alloc allocator_type;
allocator_type get_allocator() const { return allocator_type(); }

_List_base(const allocator_type&) {
///唯一的构造函数,规定了list为空时的合法状态:头结点的前后指针均指向其自身
_M_node = _M_get_node();
_M_node->_M_next = _M_node;
_M_node->_M_prev = _M_node;
}
~_List_base() {
clear();    ///将每个结点清楚
_M_put_node(_M_node);  ///将头结点归还
}

void clear();

protected:
typedef simple_alloc<_List_node<_Tp>, _Alloc> _Alloc_type;

_List_node<_Tp>* _M_get_node() { return _Alloc_type::allocate(1); }
void _M_put_node(_List_node<_Tp>* __p) { _Alloc_type::deallocate(__p, 1); }

protected:
_List_node<_Tp>* _M_node;   ///头结点指针,为实指节点类型
};

template <class _Tp, class _Alloc>
void
_List_base<_Tp,_Alloc>::clear()
{
///由于结点的_M_next均为基类指针,而基类指针不能直接初始化或者赋值给
///派生类指针,因此需要强制类型转化,已将_M_node->_M_next强制转化为其
///实质类型的指针.
_List_node<_Tp>* __cur = (_List_node<_Tp>*) (_M_node->_M_next);
while (__cur != _M_node) {
_List_node<_Tp>* __tmp = __cur;
__cur = (_List_node<_Tp>*) (__cur->_M_next);
_Destroy(&__tmp->_M_data);    ///析构结点数据元素
_M_put_node(__tmp);         ///归还结点内存
}

///使链表恢复合法状态
_M_node->_M_next = _M_node;
_M_node->_M_prev = _M_node;
}

template <class _Tp, class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp) >
class list : protected _List_base<_Tp, _Alloc> {

__STL_CLASS_REQUIRES(_Tp, _Assignable);

typedef _List_base<_Tp, _Alloc> _Base;
protected:
typedef void* _Void_pointer;

public:
typedef _Tp 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<_Tp> _Node;
typedef size_t size_type;
typedef ptrdiff_t difference_type;

typedef typename _Base::allocator_type allocator_type;
allocator_type get_allocator() const { return _Base::get_allocator(); }

public:
typedef _List_iterator<_Tp,_Tp&,_Tp*>             iterator;
typedef _List_iterator<_Tp,const _Tp&,const _Tp*> const_iterator;

typedef reverse_bidirectional_iterator<const_iterator,value_type,
const_reference,difference_type>
const_reverse_iterator;
typedef reverse_bidirectional_iterator<iterator,value_type,reference,
difference_type>
reverse_iterator;

protected:
using _Base::_M_node;
using _Base::_M_put_node;
using _Base::_M_get_node;

protected:
_Node* _M_create_node(const _Tp& __x)  ///用特定数据构造结点
{
_Node* __p = _M_get_node();
try {
_Construct(&__p->_M_data, __x);
}catch(...){
_M_put_node(__p);
}
return __p;
}

_Node* _M_create_node()   ///构造含默认值的结点
{
_Node* __p = _M_get_node();
try {
_Construct(&__p->_M_data);
}catch(...){
_M_put_node(__p);
}

return __p;
}

public:
explicit list(const allocator_type& __a = allocator_type()) : _Base(__a) {}

iterator begin()   {
///此处亦必须强制进行指针类型转化,因为iterator类构造函数只接受
///派生类指针,而_M_node->_M_next为基类指针,不能自动转化
return (_Node*)(_M_node->_M_next);
}
const_iterator begin() const { return (_Node*)(_M_node->_M_next); }

iterator end()             { return _M_node; }
const_iterator end() const { return _M_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()); }

bool empty() const { return _M_node->_M_next == _M_node; }
size_type size() const {
///list的size函数需要遍历整个list
size_type __result = 0;
distance(begin(), end(), __result);
return __result;
}
size_type max_size() const { return size_type(-1); }

reference front() { return *begin(); }
const_reference front() const { return *begin(); }
reference back() { return *(--end()); }
const_reference back() const { return *(--end()); }

///list的swap函数只需交换各自的头指针
void swap(list<_Tp, _Alloc>& __x) { __STD::swap(_M_node, __x._M_node); }

iterator insert(iterator __position, const _Tp& __x) {
///该函数只需生成一个新节点,然后修改相关指针将该节点“链”到合适位置即可
_Node* __tmp = _M_create_node(__x);
__tmp->_M_next = __position._M_node;
__tmp->_M_prev = __position._M_node->_M_prev;
__position._M_node->_M_prev->_M_next = __tmp;
__position._M_node->_M_prev = __tmp;
return __tmp;
}
iterator insert(iterator __position) { return insert(__position, _Tp()); }

/// Check whether it's an integral type.  If so, it's not an iterator.
template<class _Integer>
void _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
__true_type) {
_M_fill_insert(__pos, (size_type) __n, (_Tp) __x);
}

template <class _InputIterator>
void _M_insert_dispatch(iterator __pos,
_InputIterator __first, _InputIterator __last,
__false_type);

template <class _InputIterator>
void insert(iterator __pos, _InputIterator __first, _InputIterator __last) {
typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
_M_insert_dispatch(__pos, __first, __last, _Integral());
}

void insert(iterator __pos, size_type __n, const _Tp& __x)
{ _M_fill_insert(__pos, __n, __x); }

void _M_fill_insert(iterator __pos, size_type __n, const _Tp& __x); ///在x前插入n个x

void push_front(const _Tp& __x) { insert(begin(), __x); }
void push_front() {insert(begin());}
void push_back(const _Tp& __x) { insert(end(), __x); }
void push_back() {insert(end());}

iterator erase(iterator __position) {
_List_node_base* __next_node = __position._M_node->_M_next;
_List_node_base* __prev_node = __position._M_node->_M_prev;
_Node* __n = (_Node*) __position._M_node;
__prev_node->_M_next = __next_node;
__next_node->_M_prev = __prev_node;
_Destroy(&__n->_M_data);
_M_put_node(__n);
return iterator((_Node*) __next_node);
}
iterator erase(iterator __first, iterator __last);
void clear() { _Base::clear(); }

void resize(size_type __new_size, const _Tp& __x);
void resize(size_type __new_size) { this->resize(__new_size, _Tp()); }

void pop_front() { erase(begin()); }
void pop_back() {
iterator __tmp = end();
erase(--__tmp);
}

list(size_type __n, const _Tp& __value,
const allocator_type& __a = allocator_type()): _Base(__a)
{ insert(begin(), __n, __value); }

explicit list(size_type __n): _Base(allocator_type())
{ insert(begin(), __n, _Tp()); }

/// We don't need any dispatching tricks here, because insert does all of
/// that anyway.
template <class _InputIterator>
list(_InputIterator __first, _InputIterator __last,
const allocator_type& __a = allocator_type())
: _Base(__a)
{ insert(begin(), __first, __last); }

list(const list<_Tp, _Alloc>& __x) : _Base(__x.get_allocator())
{ insert(begin(), __x.begin(), __x.end()); }

~list() { }  ///善后留给基类中的析构函数

list<_Tp, _Alloc>& operator=(const list<_Tp, _Alloc>& __x);

public:
/// assign(), a generalized assignment member function.  Two
/// versions: one that takes a count, and one that takes a range.
/// The range version is a member template, so we dispatch on whether
/// or not the type is an integer.

void assign(size_type __n, const _Tp& __val) { _M_fill_assign(__n, __val); }

void _M_fill_assign(size_type __n, const _Tp& __val);

template <class _InputIterator>
void assign(_InputIterator __first, _InputIterator __last) {
typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
_M_assign_dispatch(__first, __last, _Integral());
}

template <class _Integer>
void _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
{ _M_fill_assign((size_type) __n, (_Tp) __val); }

template <class _InputIterator>
void _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
__false_type);

protected:
///将[first,last)从原位置中摘下来,插入到position之前
///这个函数主要通过指针的修改来完成
void transfer(iterator __position, iterator __first, iterator __last) {
if (__position != __last) {
/// Remove [first, last) from its old position.
__last._M_node->_M_prev->_M_next     = __position._M_node;
__first._M_node->_M_prev->_M_next    = __last._M_node;
__position._M_node->_M_prev->_M_next = __first._M_node;

/// Splice [first, last) into its new position.
_List_node_base* __tmp      = __position._M_node->_M_prev;
__position._M_node->_M_prev = __last._M_node->_M_prev;
__last._M_node->_M_prev     = __first._M_node->_M_prev;
__first._M_node->_M_prev    = __tmp;
}
}

public:
///将x链入本链表position之前
void splice(iterator __position, list& __x) {
if (!__x.empty())
this->transfer(__position, __x.begin(), __x.end());
}

///将i所指结点摘下来,插入到position之前
void splice(iterator __position, list&, iterator __i) {
iterator __j = __i;
++__j;
if (__position == __i || __position == __j) return;
this->transfer(__position, __i, __j);
}

void splice(iterator __position, list&, iterator __first, iterator __last) {
if (__first != __last)
this->transfer(__position, __first, __last);
}
void remove(const _Tp& __value);
void unique();
void merge(list& __x);
void reverse();
void sort();

template <class _Predicate> void remove_if(_Predicate);
template <class _BinaryPredicate> void unique(_BinaryPredicate);
template <class _StrictWeakOrdering> void merge(list&, _StrictWeakOrdering);
template <class _StrictWeakOrdering> void sort(_StrictWeakOrdering);
};

template <class _Tp, class _Alloc>
inline bool
operator==(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
{
///此处必须使用const_iterator,因const list所得到的迭代器均为const_iterator
typedef typename list<_Tp,_Alloc>::const_iterator const_iterator;
const_iterator __end1 = __x.end();
const_iterator __end2 = __y.end();

const_iterator __i1 = __x.begin();
const_iterator __i2 = __y.begin();
while (__i1 != __end1 && __i2 != __end2 && *__i1 == *__i2) {
++__i1;
++__i2;
}
return __i1 == __end1 && __i2 == __end2;
}

template <class _Tp, class _Alloc>
inline bool operator<(const list<_Tp,_Alloc>& __x,
const list<_Tp,_Alloc>& __y)
{
return lexicographical_compare(__x.begin(), __x.end(),
__y.begin(), __y.end());
}

template <class _Tp, class _Alloc>
template <class _InputIter>
void
list<_Tp, _Alloc>::_M_insert_dispatch(iterator __position,
_InputIter __first, _InputIter __last,
__false_type)
{
for ( ; __first != __last; ++__first)
insert(__position, *__first);
}

template <class _Tp, class _Alloc>
void
list<_Tp, _Alloc>::_M_fill_insert(iterator __position,
size_type __n, const _Tp& __x)
{
for ( ; __n > 0; --__n)
insert(__position, __x);
}

template <class _Tp, class _Alloc>
typename list<_Tp,_Alloc>::iterator list<_Tp, _Alloc>::erase(iterator __first,
iterator __last)
{
while (__first != __last)
erase(__first++);
return __last;
}

template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::resize(size_type __new_size, const _Tp& __x)
{
iterator __i = begin();
size_type __len = 0;
for ( ; __i != end() && __len < __new_size; ++__i, ++__len);

if (__len == __new_size)        ///__new_size <= this->size()
erase(__i, end());
else                          /// __new_size > this->size()
insert(end(), __new_size - __len, __x);
}

template <class _Tp, class _Alloc>
list<_Tp, _Alloc>& list<_Tp, _Alloc>::operator=(const list<_Tp, _Alloc>& __x)
{
if (this != &__x) {
iterator __first1 = begin();
iterator __last1 = end();
const_iterator __first2 = __x.begin();
const_iterator __last2 = __x.end();

///先挨个赋值
while (__first1 != __last1 && __first2 != __last2)
*__first1++ = *__first2++;

if (__first2 == __last2)    ///x.size() <= this->size()
erase(__first1, __last1);
else                                        ///x.size() > this->size()
insert(__last1, __first2, __last2);
}
return *this;
}

template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::_M_fill_assign(size_type __n, const _Tp& __val) {
iterator __i = begin();
for ( ; __i != end() && __n > 0; ++__i, --__n)
*__i = __val;
if (__n > 0)
insert(end(), __n, __val);
else
erase(__i, end());
}

template <class _Tp, class _Alloc>
template <class _InputIter>
void
list<_Tp, _Alloc>::_M_assign_dispatch(_InputIter __first2, _InputIter __last2,
__false_type)
{
iterator __first1 = begin();
iterator __last1 = end();
for ( ; __first1 != __last1 && __first2 != __last2; ++__first1, ++__first2)
*__first1 = *__first2;
if (__first2 == __last2)
erase(__first1, __last1);
else
insert(__last1, __first2, __last2);
}

template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::remove(const _Tp& __value)
{
iterator __first = begin();
iterator __last = end();
while (__first != __last) {
iterator __next = __first;
++__next;
if (*__first == __value) erase(__first);
__first = __next;
}
}

template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::unique()
{
iterator __first = begin();
iterator __last = end();
if (__first == __last) return;
iterator __next = __first;
while (++__next != __last) {
if (*__first == *__next)
erase(__next);
else
__first = __next;

__next = __first;
}
}

///将两个非递增排序的链表合并为一个非递增排序的链表
///合并后x链表为空
template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::merge(list<_Tp, _Alloc>& __x)
{
iterator __first1 = begin();
iterator __last1 = end();
iterator __first2 = __x.begin();
iterator __last2 = __x.end();
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);
}

///从指针p开始,将list翻转
inline void __List_base_reverse(_List_node_base* __p)
{
_List_node_base* __tmp = __p;
do {
__STD::swap(__tmp->_M_next, __tmp->_M_prev);
__tmp = __tmp->_M_prev;     /// Old next node is now prev.

} while (__tmp != __p);     ///由于是循环链表,故指针再次指向p时,说明list翻转完毕
}

template <class _Tp, class _Alloc>
inline void list<_Tp, _Alloc>::reverse()
{
__List_base_reverse(this->_M_node);
}

///由于STL sort算法要求必须为随机迭代器,因此list实现了自己的专用sort算法
///该算法采用的是归并排序的思想
template <class _Tp, class _Alloc>
void list<_Tp, _Alloc>::sort()
{
/// Do nothing if the list has length 0 or 1.
if (_M_node->_M_next != _M_node && _M_node->_M_next->_M_next != _M_node) {
list<_Tp, _Alloc> __carry;
list<_Tp, _Alloc> __counter[64];
int __fill = 0;
while (!empty()) {

__carry.splice(__carry.begin(), *this, begin());  ///__carry得到list第一个元素
int __i = 0;

///此循环将counter[__fill]之前所有非空链表合并为一个链表
while(__i < __fill && !__counter[__i].empty()) {
__counter[__i].merge(__carry);     ///此时__carry为空
__carry.swap(__counter[__i++]);    ///此时__counter[i]为空,i变为i+1
}
__carry.swap(__counter[__i]);   ///至此处i之前的所有链表均被合并至__counter[i]
if (__i == __fill) ++__fill;
}

for (int __i = 1; __i < __fill; ++__i)
__counter[__i].merge(__counter[__i-1]);

swap(__counter[__fill-1]);
}
}

template <class _Tp, class _Alloc> template <class _Predicate>
void list<_Tp, _Alloc>::remove_if(_Predicate __pred)
{
iterator __first = begin();
iterator __last = end();
while (__first != __last) {
iterator __next = __first;
++__next;      ///必须先得到下一个节点位置,再删除当前结点,否则将无法找到下一个结点
if (__pred(*__first)) erase(__first);
__first = __next;
}
}

template <class _Tp, class _Alloc> template <class _BinaryPredicate>
void list<_Tp, _Alloc>::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;
}
}

template <class _Tp, class _Alloc> template <class _StrictWeakOrdering>
void list<_Tp, _Alloc>::merge(list<_Tp, _Alloc>& __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);
}

template <class _Tp, class _Alloc> template <class _StrictWeakOrdering>
void list<_Tp, _Alloc>::sort(_StrictWeakOrdering __comp)
{
/// Do nothing if the list has length 0 or 1.
if (_M_node->_M_next != _M_node && _M_node->_M_next->_M_next != _M_node) {
list<_Tp, _Alloc> __carry;
list<_Tp, _Alloc> __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]);
}
}