容器有已用空间和可用空间，已用空间就是容器已经使用了的空间，可用空间就是指vector的大小capacity。
容器是占用一段连续线性空间，所以容器的迭代器就等价于原生态的指针（这是造成我一直以为迭代器就是指针的原因），vector迭代器类型是RandomAccessIterator类型。vector的实现依赖于前面内存的配置和内存的初始化，以及迭代器，看学习vector代码可以帮助我们更加深入理解stl_alloc.h、stl_uninitialized.h、stl_iterator.h。
下面附上代码：
G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_vector.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
* 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_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> // alloc为默认空间配置器
class vector {
public:
// 以下表示 (1),(2),(3),(4),(5)，代表 iterator_traits<I> 所服务的5个型别。
typedef T value_type; // (1)
typedef value_type* pointer; // (2)
typedef const value_type* const_pointer;
typedef const value_type* const_iterator;
typedef value_type& reference; // (3)
typedef const value_type& const_reference;
typedef size_t size_type;
typedef ptrdiff_t difference_type; // (4)
// 以下，由于vector 所维护的是一个连续性空间，所以不论其元素型別为何，
// 原生指针都可以作为其迭代器而满足所有需求。
typedef value_type* iterator;//定义迭代器的是原生态指针
/*
根据上述说法，如果客端编码如下：
vector<Shape>::iterator is;
is 的类型其实就是Shape*
而STL 內部使用 iterator_traits<is>::reference 时，获得 Shape&
使用iterator_traits<is>::iterator_category 时，获得
random_access_iterator_tag (5)
（此乃iterator_traits 针对原生态指针特化的结果）
*/
#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:
// 空间配置器。在stl_alloc.h中定义
typedef simple_alloc<value_type, Alloc> data_allocator;
/*
vector采用线性连续空间存储元素
迭代器start指向使用空间的头
迭代器end指向使用空间的尾（使用空间不是全部的空间）
end_of_storate 可用空间的尾
*/
iterator start;
iterator finish;
iterator end_of_storage;
void insert_aux(iterator position, const T& x);
void deallocate() {
if (start)
//在stl_alloc.h中定义 ,根据元素类型来判断是否调用析构函数
data_allocator::deallocate(start, end_of_storage - start);
}
void fill_initialize(size_type n, const T& value) {
start = allocate_and_fill(n, value); // 分配空间且设定初始值
finish = start + n; // 调整尾迭代器
end_of_storage = finish; // 调整迭代器。分配空间和使用空间相同
}
//对外接口，我们可以使用的
public:
iterator begin() { return start; }//返回迭代器，指向起始位置
const_iterator begin() const { return start; }
iterator end() { return finish; }//指向可用空间尾端的迭代器
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());
}
//已用用空间对象的个数
size_type size() const { return size_type(end() - begin()); }
//最大可以状态对象个数。 size_type(-1)转换为无符号数
size_type max_size() const { return size_type(-1) / sizeof(T); }
//vector当前容量
size_type capacity() const { return size_type(end_of_storage - begin()); }
//判断是否为空
bool empty() const { return begin() == end(); }
//注意，重载[]是返回引用，所以可以作为左值来给容器内对象复制
reference operator[](size_type n) { return *(begin() + n); }
const_reference operator[](size_type n) const { return *(begin() + n); }
//默认构造函数竟然不分配空间，感觉有点怪
vector() : start(0), finish(0), end_of_storage(0) {}
//以下几个构造函数（都指定大小和设置初始值都是调用 fill_initialize，在上
//面已经看到fill_initialize并不多分配空间，可见如果指定vector大小的话
//就不会再多分配空间了。
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); }
//T()说明需要容器内对象要有默认构造函数
explicit vector(size_type n) { fill_initialize(n, T()); }
//用一个容器初始化新建的容器。新建的容器大小只是x容器使用空间的大小
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;
}
//使用两个迭代器区间的值来初始化vector
#ifdef __STL_MEMBER_TEMPLATES
template <class InputIterator>
vector(InputIterator first, InputIterator last) :
start(0), finish(0), end_of_storage(0)
{
//把start、finish、end_of_storage初始化为0
//使用push_back来添加
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);//计算两个迭代器之间的距离
start = allocate_and_copy(n, first, last);//分配空间初始化，并不多分配空间
finish = start + n;
end_of_storage = finish;
}
#endif /* __STL_MEMBER_TEMPLATES */
~vector() {
//析构对象，在stl_construct.h定义
destroy(start, finish);
deallocate(); // 释放空间
}
vector<T, Alloc>& operator=(const vector<T, Alloc>& x);
//调整可用空间大小至n
void reserve(size_type n) {
if (capacity() < n) {//如果小于n则调整，大于n直接返回
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;
}
}
// 取出vector第一个元素，是返回引用
reference front() { return *begin(); }
const_reference front() const { return *begin(); }
// 取出vector最后一个元素，是返回引用
reference back() { return *(end() - 1); }
const_reference back() const { return *(end() - 1); }
// 在容器尾添加元素
void push_back(const T& x) {
if (finish != end_of_storage) { // 如果还有未用空间
construct(finish, x); // 直接初始化未用空间。
++finish;
}
else // 无未用空间
insert_aux(end(), x);
}
//交换两个vector，只是交换了迭代器，并没有重新分配内存，所以原来的迭代器不会失效
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);
}
//在position处插入元素x
iterator insert(iterator position, const T& x) {
size_type n = position - begin();
//如果插入位置正好是末尾（好像一般没这么巧吧？）
if (finish != end_of_storage && position == end()) {
construct(finish, x); // 直接初始化尾端内存。
++finish;
}
else
/*
insert_aux的实现是把position后的元素都后移，然后插入。
当然了在后移之前要看一下有没有未用空间
*/
insert_aux(position, x);
return begin() + n;
}
//直接在position处插入vector对象默认值（条用默认构造函数）
iterator insert(iterator position) { return insert(position, T()); }
#ifdef __STL_MEMBER_TEMPLATES
/*
在position处插入一段元素。
其实还是调用insert一个一个插入的，再插入过程中，移动插入位置position
*/
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 */
//在position处插入n个元素x
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);
}
//把容器末端元素去掉。并不返回末端元素
void pop_back() {
--finish;
destroy(finish);
}
// 将position处元素消除
iterator erase(iterator position) {
/*
如果position不是末端，那么要把后面元素往前移
*/
if (position + 1 != end())
copy(position + 1, finish, position);
--finish;
destroy(finish);
return position;
}
//移除两个迭代器之间的元素
iterator erase(iterator first, iterator last) {
//把last后的元素向前移
iterator i = copy(last, finish, first);
destroy(i, finish); // 析构移动后多余的元素
finish = finish - (last - first);
return first;
}
//调整已用空间大小
void resize(size_type new_size, const T& x) {
if (new_size < size())
//如果把已用空间调小，那么直接擦除掉多余部分
erase(begin() + new_size, end());
else
//已用空间变大，多出来的已用空间用x初始化
insert(end(), new_size - size(), x);
}
void resize(size_type new_size) { resize(new_size, T()); }
// 清除全部元素。
void clear() { erase(begin(), end()); }
protected:
/*
allocate_and_fill //功能：分配空间并初始化
?
allocate //分配空间 <stl_alloc.h>
?
uninitialized_fill_n //初始化 <stl_uninitialized.h>
*/
iterator allocate_and_fill(size_type n, const T& x) {
iterator result = data_allocator::allocate(n); // 配置空间
__STL_TRY {
// 全域函式，記憶體低階工具，將result所指之未初始化空間設定初值為 x，n個
//全局函数，初始化已配置但未初始化空间
// 在 <stl_uninitialized.h>。中定义
uninitialized_fill_n(result, n, x);
return result;
}
// "commit or rollback" 语义：如果有一个失败，则全部释放。
__STL_UNWIND(data_allocator::deallocate(result, n));
}
/*
allocate_and_copy //功能：分配空间并初始化
?
allocate //分配空间 <stl_alloc.h>
?
uninitialized_copy //初始化 <stl_uninitialized.h>
*/
#ifdef __STL_MEMBER_TEMPLATES
template <class ForwardIterator>
iterator allocate_and_copy(size_type n,
ForwardIterator first, ForwardIterator last) {
iterator result = data_allocator::allocate(n);//配置空间
__STL_TRY {
uninitialized_copy(first, last, result);//初始化配置空间
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 */
/*
两个迭代器之间的元素初始化vector。根据迭代器类型来选择使用哪种初始化方式
如果是 input_iterator_tag类型迭代器，则一个一个初始化
如果是 forward_iterator_tag（包含其派生类型？），则调用 allocate_and_copy
*/
#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 */
};
//判断两个容器是否相等。两个容器相同位置的元素相等才相同
//equal应该是泛型算法
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());
}
// lexicographical_compare泛型算法
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 */
//重载=号运算符
template <class T, class Alloc>
vector<T, Alloc>& vector<T, Alloc>::operator=(const vector<T, Alloc>& x) {
if (&x != this) { // 判断是否相同，防止自身赋值
if (x.size() > capacity()) { // 赋值对象x内容大于vector的capacity
//重新开辟空间
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()) { // vector空间够用
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;
}
//在指定位置插入元素
template <class T, class Alloc>
void vector<T, Alloc>::insert_aux(iterator position, const T& x) {
if (finish != end_of_storage) { // 还有可用空间
// 后移最后一个元素
construct(finish, *(finish - 1));
++finish;
// x_copy好像没啥用
T x_copy = x;
//后移那些元素
copy_backward(position, finish - 2, finish - 1);
*position = x_copy;
}
else { // 无可用空间情况
const size_type old_size = size();
const size_type len = old_size != 0 ? 2 * old_size : 1;
/*
重新开辟空间。如果原有空间为0，则重新开辟空间为1
否则新开辟空间为原有空间的2倍 。
*/
iterator new_start = data_allocator::allocate(len); // 配置空间
iterator new_finish = new_start;
__STL_TRY {
// 原有vector内容拷贝到新开辟的空间
new_finish = uninitialized_copy(start, position, new_start);
// 为新元素设定初值
construct(new_finish, x);
++new_finish;
//将旧vector未用空间的内容页拷贝过来。好像没啥用处啊？
new_finish = uninitialized_copy(position, finish, new_finish);
}
# ifdef __STL_USE_EXCEPTIONS
catch(...) {
// "commit or rollback" 若失败则全部回滚。
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
# endif /* __STL_USE_EXCEPTIONS */
// 析构和释放 vector
destroy(begin(), end());
deallocate();
// 调整迭代器
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}
//在position处插入n个元素，初值为x
template <class T, class Alloc>
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) {
if (n != 0) { // n=0的话无意义
//可用空间够用
if (size_type(end_of_storage - finish) >= n) {
// 定义x_copy=x;看起来好像没啥用，是不是多线程或者担心引用会修改原来的值？
T x_copy = x;
// position处到尾端共有多少个元素
const size_type elems_after = finish - position;
iterator old_finish = finish;
/*
要判断 position处到尾端元素个数是否大于新插入元素个数n
因为在finish之前的内存是已经初始化的，finishing之后的内存是为构建的
*/
if (elems_after > n) { //position处到尾端元素个数大于新插入元素个数n
uninitialized_copy(finish - n, finish, finish);
finish += n; // 將vector 尾端標記後移
copy_backward(position, old_finish - n, old_finish);
fill(position, position + n, x_copy); // 從安插點開始填入新值
}
else { //position处到尾端元素个数小于新插入元素个数n
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 {
/*
空间不够用，则开辟新空间。新空间大小不是简单的乘以2，因为乘以2也
未必容得下新加入的元素
*/
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_fill_n(new_finish, n, x);
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;
}
}
}
//在position处插入两个迭代器之间的元素。迭代器不同，实现方法不同，上面已经讲过。
#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 */
//在position处插入两个迭代器之间的元素，和在position处插入n个元素类似
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: