- 容器vector的代码如下:
- sizeof(vector
) = 12Byte(32位下3个4字节的指针)
- sizeof(vector
template<class T, class Alloc= alloc>
class vector {
public:
typedef T value_type;
typedef value_type* iterator;
typedef value_type& reference;
typedef size_t size_type;
protected:
iterator start;
iterator finish;
iterator end_of_storage;
public:
iterator begin() { return start; }
iterator end() { return finish; }
size_type size() const { return size_type(end() - begin()); }
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); }
reference front() { return *begin(); }
reference back() { return *(end() - 1); }
};
vector的内存分布
- start指向第一个元素
- finish指向最后一个元素的下一个元素
- end_of_storage指向最大容量的内存块的下一个位置
- size是当前大小
- capacity是当前vector的最大容量
- vector对使用者是连续的,因此重载了[]运算符.
- vector的实现也是连续的,因此使用指针类型做迭代器(即迭代器vector
::iterator的实际类型是原生指针T*).
vector的内存扩容
- vector::push_back方法先判断内存空间是否满,若内存空间不满则直接插入;若内存空间满则调用insert_aux函数先扩容两倍再插入元素.
void push_back(const T &x) { if (finish != end_of_storage) { // 尚有备用空间,则直接插入,并调整finish迭代器 construct(finish, x); // 全局函数 ++finish; // 调整finsh位置 } else // 已无备用空间则调用 insert_aux 先扩容再插入元素 insert_aux(end(), x); } insert_aux被设计用于在容器任意位置插入元素,在容器内存空间不足会现将原有容器扩容.
template<class T, class Alloc> void vector<T, Alloc>::insert_ux(iterator position, const T &x) { // 这里的重复检测工作是因为这个函数除了给push_back使用还会给其他函数使用(比如insert) if (finish != end_of_storage) { // 尚有备用空间,则将插入点后元素后移一位并插入元素 construct(finish, *(finish - 1)); // 以vector最后一个元素值为新节点的初值 ++finish; T x_copy = x; copy_backward(position, finish - 2, finish - 1); *position = x_copy; } else { // 已无备用空间,则先扩容,再插入 const size_type old_size = size(); const size_type len = old_size != 0 ?: 2 * old_size:1; // 分配原则:如果原大小为0,则分配1(个元素大小) // 如果原大小不为0,则分配原大小的2倍. // 前半段用来放置原数据,后半段准备用来放置新数据 iterator new_start = data_allocator::allocate(len); iterator new_finish = new_start; try { new_finish = uninitialized_copy(start, position, new_start); // 拷贝插入点前的元素 construct(new_finish, x); // 插入新元素并调整水位 ++new_finish; new_finish = uninitialized_copy(position, finish, new_finish); // 拷贝插入点后的元素,用于保证insert操作的准确性 } catch (expection e) { // 插入失败则回滚,释放内存并抛出错误 destroy(new_start, new_finish) : data_allocator::deallocate(new_start, len); throw; } // 释放原容器所占内存 destroy(begin(), end()); deallocate(); // 调整迭代器 start = new_start; finish = new_finish; end_of_storage = new_start + len; } };
gcc2.9的vector源码
//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> // 預設使用 alloc 為配置器
class vector {
public:
// 以下標示 (1),(2),(3),(4),(5)，代表 iterator_traits<I> 所服務的5個型別。
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，由於vector 所維護的是一個連續線性空間，所以不論其元素型別為何，
// 原生指標都可以做為其迭代器而滿足所有需求。
typedef value_type* iterator;
/* 根據上述寫法，如果客端寫出這樣的碼：
vector<Shape>::iterator is;
is 的型別其實就是Shape*
而STL 內部運用 iterator_traits<is>::reference 時，獲得 Shape&
運用iterator_traits<is>::iterator_category 時，獲得
random_access_iterator_tag (5)
（此乃iterator_traits 針對原生指標的特化結果）
*/
#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:
// 專屬之空間配置器，每次配置一個元素大小
typedef simple_alloc<value_type, Alloc> data_allocator;
// vector採用簡單的線性連續空間。以兩個迭代器start和end分別指向頭尾，
// 並以迭代器end_of_storage指向容量尾端。容量可能比(尾-頭)還大，
// 多餘即備用空間。
iterator start;
iterator finish;
iterator end_of_storage;
void insert_aux(iterator position, const T& x);
void deallocate() {
if (start)
data_allocator::deallocate(start, end_of_storage - start);
}
void fill_initialize(size_type n, const T& value) {
start = allocate_and_fill(n, value); // 配置空間並設初值
finish = start + n; // 調整水位
end_of_storage = finish; // 調整水位
}
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) {}
// 以下建構式，允許指定大小 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); // 全域函式，建構/解構基本工具。
deallocate(); // 先前定義好的成員函式
}
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;
}
}
// 取出第一個元素內容
reference front() { return *begin(); }
const_reference front() const { return *begin(); }
// 取出最後一個元素內容
reference back() { return *(end() - 1); }
const_reference back() const { return *(end() - 1); }
// 增加一個元素，做為最後元素
void push_back(const T& x) {
if (finish != end_of_storage) { // 還有備用空間
construct(finish, x); // 直接在備用空間中建構元素。
++finish; // 調整水位高度
}
else // 已無備用空間
insert_aux(end(), x);
}
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); // 全域函式，建構/解構基本工具。
++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;
destroy(finish); // 全域函式，建構/解構基本工具。
}
// 將迭代器 position 所指之元素移除
iterator erase(iterator position) {
if (position + 1 != end()) // 如果 p 不是指向最後一個元素
// 將 p 之後的元素一一向前遞移
copy(position + 1, finish, position);
--finish; // 調整水位
destroy(finish); // 全域函式，建構/解構基本工具。
return position;
}
iterator erase(iterator first, iterator last) {
iterator i = copy(last, finish, first);
destroy(i, finish); // 全域函式，建構/解構基本工具。
finish = finish - (last - first);
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()); }
// 清除全部元素。注意，並未釋放空間，以備可能未來還會新加入元素。
void clear() { erase(begin(), end()); }
protected:
iterator allocate_and_fill(size_type n, const T& x) {
iterator result = data_allocator::allocate(n); // 配置n個元素空間
__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
// 定義於 <stl_uninitialized.h>。
uninitialized_fill_n(result, n, x);
return result;
}
// "commit or rollback" 語意：若非全部成功，就一個不留。
__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) { // 判斷是否 self-assignment
if (x.size() > capacity()) { // 如果標的物比我本身的容量還大
iterator tmp = allocate_and_copy(x.end() - x.begin(),
x.begin(), x.end());
destroy(start, finish); // 把整個舊的vector 摧毀
deallocate(); // 釋放舊空間
start = tmp; // 設定指向新空間
end_of_storage = start + (x.end() - x.begin());
}
else if (size() >= x.size()) { // 如果標的物大小 <= 我的大小
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) { // 還有備用空間
// 在備用空間起始處建構一個元素，並以vector 最後一個元素值為其初值。
construct(finish, *(finish - 1));
// 調整水位。
++finish;
// 以下做啥用？
T x_copy = x;
copy_backward(position, finish - 2, finish - 1);
*position = x_copy;
}
else { // 已無備用空間
const size_type old_size = size();
const size_type len = old_size != 0 ? 2 * old_size : 1;
// 以上配置原則：如果原大小為0，則配置 1（個元素大小）；
// 如果原大小不為0，則配置原大小的兩倍，
// 前半段用來放置原資料，後半段準備用來放置新資料。
iterator new_start = data_allocator::allocate(len); // 實際配置
iterator new_finish = new_start;
__STL_TRY {
// 將原vector 的內容拷貝到新 vector。
new_finish = uninitialized_copy(start, position, new_start);
// 為新元素設定初值x
construct(new_finish, x);
// 調整水位。
++new_finish;
// 將原vector 的備用空間中的內容也忠實拷貝過來（啥用途？）
new_finish = uninitialized_copy(position, finish, new_finish);
}
# ifdef __STL_USE_EXCEPTIONS
catch(...) {
// "commit or rollback" 語意：若非全部成功，就一個不留。
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
# endif /* __STL_USE_EXCEPTIONS */
// 解構並釋放原 vector
destroy(begin(), end());
deallocate();
// 調整迭代器，指向新vector
start = new_start;
finish = new_finish;
end_of_storage = new_start + len;
}
}
// 從 position 開始，安插 n 個元素，元素初值為 x
template <class T, class Alloc>
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) {
if (n != 0) { // 當 n != 0 才進行以下所有動作
if (size_type(end_of_storage - finish) >= n) {
// 備用空間大於等於「新增元素個數」
T x_copy = x;
// 以下計算安插點之後的現有元素個數
const size_type elems_after = finish - position;
iterator old_finish = finish;
if (elems_after > n) {
// 「安插點之後的現有元素個數」大於「新增元素個數」
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 {
// 「安插點之後的現有元素個數」小於等於「新增元素個數」
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 {
// 備用空間小於「新增元素個數」（那就必須配置額外的記憶體）
// 首先決定新長度：舊長度的兩倍，或舊長度+新增元素個數。
const size_type old_size = size();
const size_type len = old_size + max(old_size, n);
// 以下配置新的vector 空間
iterator new_start = data_allocator::allocate(len);
iterator new_finish = new_start;
__STL_TRY {
// 以下首先將舊vector 的安插點之前的元素複製到新空間。
new_finish = uninitialized_copy(start, position, new_start);
// 以下再將新增元素（初值皆為 n）填入新空間。
new_finish = uninitialized_fill_n(new_finish, n, x);
// 以下再將舊vector 的安插點之後的元素複製到新空間。
new_finish = uninitialized_copy(position, finish, new_finish);
}
# ifdef __STL_USE_EXCEPTIONS
catch(...) {
// 如有異常發生，實現 "commit or rollback" semantics.
destroy(new_start, new_finish);
data_allocator::deallocate(new_start, len);
throw;
}
# endif /* __STL_USE_EXCEPTIONS */
// 以下清除並釋放舊的 vector
destroy(start, finish);
deallocate();
// 以下調整水位標記
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: