STL源码剖析 容器 stl_vector.h

本文为senlie原创，转载请保留此地址：http://blog.csdn.net/zhengsenlie

vector

----------------------------------------------------------------------

描述：

1.迭代器

vector 维护的是一个连续线性空间，它的迭代器是普通指针，

能满足 RandomAccessIterator 所有必要条件：operator*, operator->,operator++,operator--,operator+,

operator-,operator+=,operator-=,operator[]

2.数据结构

vector所采用的数据结构是线性连续空间。

迭代器 start、finish分别表示配置得来的连续空间中目前已经被使用的范围

迭代器 end_of_storage 指向整块连续空间的尾端

增加新元素时，如果走过当时的容量，则容量会扩充至两倍。

如果两倍容量仍不足，就扩张至足够大的容量。

扩充容量的过程为：重新配置、元素移动、释放原空间

所谓动态增加大小，并不是在原空间之后接续新空间，因为无法保证原空间之后

尚有可供配置的空间。因此，对 vector 的任何操作，一旦引起空间重新配置，

指向原 vector 的所有迭代器就失效了。



示例：

vector<int> V;
V.insert(V.begin(), 3);
assert(V.size() == 1 && V.capacity() >= 1 && V[0] == 3);

源码：

#ifndef __SGI_STL_INTERNAL_VECTOR_H
#define __SGI_STL_INTERNAL_VECTOR_H

__STL_BEGIN_NAMESPACE

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

template <class T, class Alloc = alloc>
class vector {
public:
typedef T value_type;
typedef value_type* pointer;
typedef const value_type* const_pointer;
typedef value_type* iterator; //vector 的迭代器是个原生的指针
typedef const value_type* const_iterator;
typedef value_type& reference;
typedef const value_type& const_reference;
typedef size_t size_type;
typedef ptrdiff_t difference_type;

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
typedef reverse_iterator<const_iterator> const_reverse_iterator;
typedef reverse_iterator<iterator> reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
typedef reverse_iterator<const_iterator, value_type, const_reference,
difference_type>  const_reverse_iterator;
typedef reverse_iterator<iterator, value_type, reference, difference_type>
reverse_iterator;
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
protected:
typedef simple_alloc<value_type, Alloc> data_allocator; //连续空间？
iterator start; //表示目前使用空间的头
iterator finish; //表示目前使用空间的尾
iterator end_of_storage; //表示目前可用空间的尾
void insert_aux(iterator position, const T& x);
void deallocate() {
if (start) data_allocator::deallocate(start, end_of_storage - start);
}
// 填充并予以初始化
void fill_initialize(size_type n, const T& value) {
start = allocate_and_fill(n, value);
finish = start + n;
end_of_storage = finish;
}
public:
iterator begin() { return start; }
const_iterator begin() const { return start; }
iterator end() { return finish; }
const_iterator end() const { return finish; }
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());
}
size_type size() const { return size_type(end() - begin()); }
size_type max_size() const { return size_type(-1) / sizeof(T); }
size_type capacity() const { return size_type(end_of_storage - begin()); }
bool empty() const { return begin() == end(); }
reference operator[](size_type n) { return *(begin() + n); }
const_reference operator[](size_type n) const { return *(begin() + n); }

vector() : start(0), finish(0), end_of_storage(0) {}
//构造函数，允许指定 vector 大小 n 和初值 value
vector(size_type n, const T& value) { fill_initialize(n, value); }
vector(int n, const T& value) { fill_initialize(n, value); }
vector(long n, const T& value) { fill_initialize(n, value); }
explicit vector(size_type n) { fill_initialize(n, T()); }

vector(const vector<T, Alloc>& x) {
start = allocate_and_copy(x.end() - x.begin(), x.begin(), x.end());
finish = start + (x.end() - x.begin());
end_of_storage = finish;
}
#ifdef __STL_MEMBER_TEMPLATES
template <class InputIterator>
vector(InputIterator first, InputIterator last) :
start(0), finish(0), end_of_storage(0)
{
range_initialize(first, last, iterator_category(first));
}
#else /* __STL_MEMBER_TEMPLATES */
vector(const_iterator first, const_iterator last) {
size_type n = 0;
distance(first, last, n);
start = allocate_and_copy(n, first, last);
finish = start + n;
end_of_storage = finish;
}
#endif /* __STL_MEMBER_TEMPLATES */
~vector() {
destroy(start, finish);
deallocate();
}
vector<T, Alloc>& operator=(const vector<T, Alloc>& x);
void reserve(size_type n) {
if (capacity() < n) {
const size_type old_size = size();
iterator tmp = allocate_and_copy(n, start, finish);
destroy(start, finish);
deallocate();
start = tmp;
finish = tmp + old_size;
end_of_storage = start + n;
}
}
reference front() { return *begin(); }
const_reference front() const { return *begin(); }
reference back() { return *(end() - 1); }
const_reference back() const { return *(end() - 1); }
//
void push_back(const T& x) {
if (finish != end_of_storage) { //检查是否还有备用空间
construct(finish, x); //有，直接在备用空间上构造元素
++finish; //调整迭代器 finish
}
else
insert_aux(end(), x); //没有，扩充空间(重新配置、元素移动、释放原空间)
}
void swap(vector<T, Alloc>& x) {
__STD::swap(start, x.start);
__STD::swap(finish, x.finish);
__STD::swap(end_of_storage, x.end_of_storage);
}
iterator insert(iterator position, const T& x) {
size_type n = position - begin();
if (finish != end_of_storage && position == end()) {
construct(finish, x);
++finish;
}
else
insert_aux(position, x);
return begin() + n;
}
iterator insert(iterator position) { return insert(position, T()); }
#ifdef __STL_MEMBER_TEMPLATES
template <class InputIterator>
void insert(iterator position, InputIterator first, InputIterator last) {
range_insert(position, first, last, iterator_category(first));
}
#else /* __STL_MEMBER_TEMPLATES */
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);
}

void pop_back() {
--finish; //将尾端标记往前移一格，表示将放弃尾端元素
destroy(finish); //析构尾端元素
}
//清除 position 指向的元素
iterator erase(iterator position) {
if (position + 1 != end())
copy(position + 1, finish, position);
--finish;
destroy(finish);
return position;
}
//清除[first, last)中的所有元素
iterator erase(iterator first, iterator last) {
iterator i = copy(last, finish, first); //将 [last, finish) 指示的元素拷贝至 first 迭代器开头的地方
destroy(i, finish); //析构[i, finish) 里的元素
finish = finish - (last - first); //调整 finish 指示的位置 last - first 表示清除掉了的元素个数
return first;
}
void resize(size_type new_size, const T& x) {
if (new_size < size())
erase(begin() + new_size, end());
else
insert(end(), new_size - size(), x);
}
void resize(size_type new_size) { resize(new_size, T()); }
//调用 erase 清除所有元素
void clear() { erase(begin(), end()); }

protected:
//配置而后填充
iterator allocate_and_fill(size_type n, const T& x) {
iterator result = data_allocator::allocate(n); //配置 n 个元素空间
__STL_TRY {
uninitialized_fill_n(result, n, x); //全局函数。全根据 result 的类型特性(type traits)决定使用算法 fill_n() 或反复调用  construct() 来完成任务
return result;
}
__STL_UNWIND(data_allocator::deallocate(result, n));
}

#ifdef __STL_MEMBER_TEMPLATES
template <class ForwardIterator>
iterator allocate_and_copy(size_type n,
ForwardIterator first, ForwardIterator last) {
iterator result = data_allocator::allocate(n);
__STL_TRY {
uninitialized_copy(first, last, result);
return result;
}
__STL_UNWIND(data_allocator::deallocate(result, n));
}
#else /* __STL_MEMBER_TEMPLATES */
iterator allocate_and_copy(size_type n,
const_iterator first, const_iterator last) {
iterator result = data_allocator::allocate(n);
__STL_TRY {
uninitialized_copy(first, last, result);
return result;
}
__STL_UNWIND(data_allocator::deallocate(result, n));
}
#endif /* __STL_MEMBER_TEMPLATES */

#ifdef __STL_MEMBER_TEMPLATES
template <class InputIterator>
void range_initialize(InputIterator first, InputIterator last,
input_iterator_tag) {
for ( ; first != last; ++first)
push_back(*first);
}

// This function is only called by the constructor.  We have to worry
//  about resource leaks, but not about maintaining invariants.
template <class ForwardIterator>
void range_initialize(ForwardIterator first, ForwardIterator last,
forward_iterator_tag) {
size_type n = 0;
distance(first, last, n);
start = allocate_and_copy(n, first, last);
finish = start + n;
end_of_storage = finish;
}

template <class InputIterator>
void range_insert(iterator pos,
InputIterator first, InputIterator last,
input_iterator_tag);

template <class ForwardIterator>
void range_insert(iterator pos,
ForwardIterator first, ForwardIterator last,
forward_iterator_tag);

#endif /* __STL_MEMBER_TEMPLATES */
};

template <class T, class Alloc>
inline bool operator==(const vector<T, Alloc>& x, const vector<T, Alloc>& y) {
return x.size() == y.size() && equal(x.begin(), x.end(), y.begin());
}

template <class T, class Alloc>
inline bool operator<(const vector<T, Alloc>& x, const vector<T, Alloc>& y) {
return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER

template <class T, class Alloc>
inline void swap(vector<T, Alloc>& x, vector<T, Alloc>& y) {
x.swap(y);
}

#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

template <class T, class Alloc>
vector<T, Alloc>& vector<T, Alloc>::operator=(const vector<T, Alloc>& x) {
if (&x != this) {
if (x.size() > capacity()) {
iterator tmp = allocate_and_copy(x.end() - x.begin(),
x.begin(), x.end());
destroy(start, finish);
deallocate();
start = tmp;
end_of_storage = start + (x.end() - x.begin());
}
else if (size() >= x.size()) {
iterator i = copy(x.begin(), x.end(), begin());
destroy(i, finish);
}
else {
copy(x.begin(), x.begin() + size(), start);
uninitialized_copy(x.begin() + size(), x.end(), finish);
}
finish = start + x.size();
}
return *this;
}

template <class T, class Alloc>
void vector<T, Alloc>::insert_aux(iterator position, const T& x) {
if (finish != end_of_storage) { // 不是备用空间不够才会调用 insert_aux 来插入元素吗？ 为什么还会出现 finish != end_of_storage 的情况 ？
// --> 除了 push_back 不够空间时会调用 insert_aux，正常的 insert 也是调用 insert_aux 实现的。

//为什么不直接 copy_backward(position, finish - 1, finish)， 然后 *position = x_copy 呢？
construct(finish, *(finish - 1));
++finish;
T x_copy = x;
copy_backward(position, finish - 2, finish - 1);
*position = x_copy;
}
else { //无备用空间 position == finish
const size_type old_size = size();
const size_type len = old_size != 0 ? 2 * old_size : 1;
//如果原大小为0，则配置1个元素大小的空间，否则配置原大小两倍的空间
iterator new_start = data_allocator::allocate(len); //实际配置
iterator new_finish = new_start;
__STL_TRY {
//将原空间的全部内容拷贝到新空间 positition
new_finish = uninitialized_copy(start, position, new_start);
//为新元素设定初值 x
construct(new_finish, x);
//调整迭代器 finish
++new_finish;
//？？我觉得下面这行代码没用。因为无备用空间的情况，position == finish
new_finish = uninitialized_copy(position, finish, new_finish);
}

#       ifdef  __STL_USE_EXCEPTIONS
catch(...) { //异常竟然可以用三个小点 ... ??
//回滚
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
#       endif /* __STL_USE_EXCEPTIONS */

//析构并释放原空间
destroy(begin(), end());
deallocate();
//调整迭代器，指向新 vector
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}

template <class T, class Alloc>
//从 position 开始，插入 n 个元素，元素初值为 x
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) {
if (n != 0) { // 当 n != 0 才进行以下所有操作
if (size_type(end_of_storage - finish) >= n) { //备用空间大于新增元素个数
T x_copy = x;
const size_type elems_after = finish - position; //插入点之后的的现有元素个数
iterator old_finish = finish;
if (elems_after > n) { //"插入点之后的的现有元素个数"大于"新增元素个数"
//空间还没初始化时用 uninitialized_copy ， 已经初始化了用 copy_backward
uninitialized_copy(finish - n, finish, finish);
finish += n;
copy_backward(position, old_finish - n, old_finish);
fill(position, position + n, x_copy); //从插入点开始填入新值
}
else { //"插入点之后的的现有元素个数"小于"新增元素个数"
uninitialized_fill_n(finish, n - elems_after, x_copy);
finish += n - elems_after;
uninitialized_copy(position, old_finish, finish);
finish += elems_after;
fill(position, old_finish, x_copy);
}
}
else {//备用空间小于新增元素个数
const size_type old_size = size();
// 首先决定新长度：旧长度的两倍或旧长度+新元素个数，这两个中取最大值
const size_type len = old_size + max(old_size, n);
iterator new_start = data_allocator::allocate(len);
iterator new_finish = new_start;
__STL_TRY {
//先用 uninitialized_copy 将旧 vector 的插入点之前的元素复制到新空间
new_finish = uninitialized_copy(start, position, new_start);
//再用 uninitialized_fill_n 将新增元素填入新空间
new_finish = uninitialized_fill_n(new_finish, n, x);
//最后再用 uninitialized_copy 将旧 vector 的插入点之后的元素复制到新空间
new_finish = uninitialized_copy(position, finish, new_finish);
}
#         ifdef  __STL_USE_EXCEPTIONS
catch(...) {
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
#         endif /* __STL_USE_EXCEPTIONS */
//清除并释放旧的 vector
destroy(start, finish);
deallocate();
//调整标记
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}
}

#ifdef __STL_MEMBER_TEMPLATES

template <class T, class Alloc> template <class InputIterator>
void vector<T, Alloc>::range_insert(iterator pos,
InputIterator first, InputIterator last,
input_iterator_tag) {
for ( ; first != last; ++first) {
pos = insert(pos, *first);
++pos;
}
}

template <class T, class Alloc> template <class ForwardIterator>
void vector<T, Alloc>::range_insert(iterator position,
ForwardIterator first,
ForwardIterator last,
forward_iterator_tag) {
if (first != last) {
size_type n = 0;
distance(first, last, n);
if (size_type(end_of_storage - finish) >= n) {
const size_type elems_after = finish - position;
iterator old_finish = finish;
if (elems_after > n) {
uninitialized_copy(finish - n, finish, finish);
finish += n;
copy_backward(position, old_finish - n, old_finish);
copy(first, last, position);
}
else {
ForwardIterator mid = first;
advance(mid, elems_after);
uninitialized_copy(mid, last, finish);
finish += n - elems_after;
uninitialized_copy(position, old_finish, finish);
finish += elems_after;
copy(first, mid, position);
}
}
else {
const size_type old_size = size();
const size_type len = old_size + max(old_size, n);
iterator new_start = data_allocator::allocate(len);
iterator new_finish = new_start;
__STL_TRY {
new_finish = uninitialized_copy(start, position, new_start);
new_finish = uninitialized_copy(first, last, new_finish);
new_finish = uninitialized_copy(position, finish, new_finish);
}
#         ifdef __STL_USE_EXCEPTIONS
catch(...) {
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
#         endif /* __STL_USE_EXCEPTIONS */
destroy(start, finish);
deallocate();
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}
}

#else /* __STL_MEMBER_TEMPLATES */

template <class T, class Alloc>
void vector<T, Alloc>::insert(iterator position,
const_iterator first,
const_iterator last) {
if (first != last) {
size_type n = 0;
distance(first, last, n);
if (size_type(end_of_storage - finish) >= n) {
const size_type elems_after = finish - position;
iterator old_finish = finish;
if (elems_after > n) {
uninitialized_copy(finish - n, finish, finish);
finish += n;
copy_backward(position, old_finish - n, old_finish);
copy(first, last, position);
}
else {
uninitialized_copy(first + elems_after, last, finish);
finish += n - elems_after;
uninitialized_copy(position, old_finish, finish);
finish += elems_after;
copy(first, first + elems_after, position);
}
}
else {
const size_type old_size = size();
const size_type len = old_size + max(old_size, n);
iterator new_start = data_allocator::allocate(len);
iterator new_finish = new_start;
__STL_TRY {
new_finish = uninitialized_copy(start, position, new_start);
new_finish = uninitialized_copy(first, last, new_finish);
new_finish = uninitialized_copy(position, finish, new_finish);
}
#         ifdef __STL_USE_EXCEPTIONS
catch(...) {
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
#         endif /* __STL_USE_EXCEPTIONS */
destroy(start, finish);
deallocate();
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}
}

#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_VECTOR_H */

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