C++中vector的实现



注意几点：

分配内存不要使用new和delete，因为new的同时就把对象构造了，而我们需要的是原始内存。

所以应该使用标准库提供的allocator类来实现内存的控制。当然也可以重载operator new操作符，因为二者都是使用malloc作为底层实现，所以直接采用malloc也可以。

对象的复制必须使用系统提供的uninitialized_fill和uninitialized_copy，因为我们无法手工调用构造函数。

对于C++中的对象，除了POD之外，使用memcpy系列的函数是绝对错误的。

myvector.h

#ifndef _VECTOR_H_#define _VECTOR_H_#include <stddef.h>#include <algorithm>#include <memory>template <typename T>class Vector{    public:        typedef T *iterator;        typedef const T *const_iterator;         typedef size_t size_type;        typedef T value_type;        class reverse_iterator        {            public:                reverse_iterator(iterator it = NULL):current_(it) {}                iterator base() const { return current_; }                reverse_iterator &operator++()//前置                {                    --current_;                    return *this;                 }                reverse_iterator operator++(int)//后置                {                    reverse_iterator temp(*this);                    --current_;                    return temp;                }                reverse_iterator &operator--()                 {                    ++current_;                    return *this;                 }                reverse_iterator operator--(int)                {                    reverse_iterator temp(*this);                    ++current_;                     return temp;                 }                T &operator*()                {                    iterator temp = current_;                    return *--temp;                 }                T *operator->()                  {                    iterator temp = current_;                    return --temp;                }                friend bool operator==(const reverse_iterator &lhs,                         const reverse_iterator &rhs)                {                    return lhs.current_ == rhs.current_;                }                friend bool operator!=(const reverse_iterator &lhs,                         const reverse_iterator &rhs)                {                    return lhs.current_ != rhs.current_;                }            private:                iterator current_;        };        Vector() { create(); }//无参构造函数        explicit Vector(size_type n, const T &t = T()) { create(n, t); }        Vector(const Vector &v) { create(v.begin(), v.end());}// 拷贝构造函数        ~Vector() { uncreate();}        Vector &operator=(const Vector &other);        T &operator[] (size_type i) { return data_[i]; }        const T &operator[] (size_type i) const {return data_[i]; }        void push_back(const T &t);        size_type size() const { return avail_ - data_;}        size_type capacity()const { return limit_ - data_;}        iterator begin() { return data_; }        const_iterator begin() const {return data_;}        iterator end() {return avail_;}        const_iterator end() const { return avail_; }        reverse_iterator rbegin(){return reverse_iterator(end());}        reverse_iterator rend() {return reverse_iterator(begin());}        void swap(Vector &rhs)        {            std::swap(data_, rhs.data_);            std::swap(avail_, rhs.avail_);            std::swap(limit_, rhs.limit_);        }    private:        iterator data_;//首元素        iterator avail_;//末尾元素的下一个        iterator limit_;        std::allocator<T> alloc_;//内存分配器        void create();        void create(size_type, const T &);        void create(const_iterator, const_iterator);        void  uncreate();        void grow();        void uncheckAppend(const T &);};    template <typename T>inline Vector<T> &Vector<T>::operator=(const Vector &rhs){    if(this != rhs)    {        uncreate();//释放原来的内存        create(rhs.begin(), rhs.end());    }    return *this;}    template <typename T>inline void Vector<T>::push_back(const T &t){    if(avail_ == limit_)    {        grow();    }    uncheckAppend(t);}    template <typename T>inline void Vector<T>::create(){    //分配空的数组    data_ = avail_ = limit_ = 0;}    template <typename T>inline void Vector<T>::create(size_type n, const T &val){    //分配原始内存    data_ = alloc_.allocate(n);    limit_ = avail_ = data_ + n;    //向原始内存填充元素    std::uninitialized_fill(data_, limit_, val);}    template <typename T>inline void Vector<T>::create(const_iterator i, const_iterator j){    data_ = alloc_.allocate(j-i);    limit_ = avail_ = std::uninitialized_copy(i, j, data_);}    template <typename T>inline void Vector<T>::uncreate(){    if(data_)//逐个析构    {        iterator it = avail_;        while(it != data_)        {            alloc_.destroy(--it);        }        alloc_.deallocate(data_, limit_ - data_ );//真正释放内存    }    data_ = limit_ = avail_ = 0;//重置指针}    template <typename T>inline void Vector<T>::grow(){    //内存变为2倍    size_type new_size = std::max(2 * (limit_ - data_), std::ptrdiff_t(1));    //分配原始内存    iterator new_data = alloc_.allocate(new_size);    //复制元素    iterator new_avail = std::uninitialized_copy(data_, avail_, new_data);    uncreate();//释放以前内存    data_ = new_data;    avail_ = new_avail;    limit_ = data_ + new_size;}    template <typename T>inline void Vector<T>::uncheckAppend(const T &val){    alloc_.construct(avail_++, val);}#endif /*VECTOR_H*/ 

test_main.cpp

#include "myvector.h"#include <iostream>#include <string>using namespace std;void print_reverse(Vector<string> &vec){    cout << "reverse_iterator: " << endl;    for(Vector<string>::reverse_iterator it = vec.rbegin();             it != vec.rend();             ++it)    {        cout << *it << endl;        }    cout << endl;}void print(Vector<string> &vec){    cout << "iterator: " << endl;    for(Vector<string>::iterator it = vec.begin();             it != vec.end();             ++it)    {        cout << *it << endl;        }    cout << endl;}int main(int argc, const char *argv[]){    Vector<string> vec(3, "hello");    for(Vector<string>::const_iterator it = vec.begin();         it != vec.end();         ++it)    {        cout << *it << endl;        }   cout << endl;       cout << "size=" << vec.size() << endl;    cout << "capacity:" << vec.capacity() << endl;    vec.push_back("foo");    vec.push_back("bar");    cout << "size:=" << vec.size() << endl;    cout << "capacity=" << vec.capacity() << endl;    print_reverse(vec);   print(vec);    return 0;}

转自：http://www.cnblogs.com/inevermore/p/4003710.html