vector的简易实现

　　vector的简易实现整理自《数据结构与算法分析–C++描述（第3版）》3.4节“向量的实现”。详细可参考《STL源码分析》4.2节。

　　具体实现代码如下：

#ifndef VECTOR_H
#define VECTOR_H

#include <iostream>
using namespace std;

template<class T>
class Vector
{
private:
    int theSize;
    int theCapacity;
    T *objects;

public:
    typedef T* iterator;
    typedef const T* const_iterator;
    enum{ SPARE_CAPACITY = 16 };

public:
    explicit Vector(int initSize = 0);    //用explicit避免隐式类型转换
    ~Vector();
    Vector(const Vector<T>& rhs);
    const Vector<T>& operator=(const Vector<T>& rhs);

    void resize(int newSize);
    void reserve(int newCapacity);

    T& operator[](int index);
    const T& operator[](int index) const;

    bool empty() const;
    int size() const;
    int capacity() const;

    void push_back(const T& x);
    void pop_back();
    const T& back() const;

    iterator begin();
    const_iterator begin() const;

    iterator end();
    const_iterator end() const;

};

template<class T>
Vector<T>::Vector(int initSize = 0) : theSize(initSize), theCapacity(initSize + SPARE_CAPACITY)
{
    objects = new T[theCapacity];
}

template<class T>
Vector<T>::~Vector()
{
    delete []objects;
}

template<class T>
Vector<T>::Vector(const Vector<T>& rhs) : objects(nullptr)
{
    operator = (rhs);
}

template<class T>
const Vector<T>& Vector<T>::operator=(const Vector<T>& rhs)
{
    if (this != &rhs)
    {
        delete[]objects;
        theSize = rhs.size();
        theCapcity = rhs.theCapacity;

        // 注意是深拷贝
        objects = new T[capacity()];
        for (int k = 0; k < size(); k++)
            objects[k] = rhs.objects[k];
    }

    return *this;
}

template<class T>
void Vector<T>::resize(int newSize)
{
    if (newSize > theCapacity)
        reserve(newSize * 2 + 1);    //每次空间不够的时候,就重新获得2倍于当前容量的空间,+1是为了防止0的情况
    theSize = newSize;
}

template<class T>
void Vector<T>::reserve(int newCapacity)
{
    if (newCapacity < theSize)
        return;

    T *oldArray = objects;

    // 之所以需要将老的数组复制到新的数组，是因为要保证Vector整块内存的连续性
    objects = new T[newCapacity];
    for (int k = 0; k < theSize; k++)
        objects[k] = oldArray[k];

    theCapacity = newCapacity;

    delete []oldArray;
}

template<class T>
T& Vector<T>::operator[](int index)
{
    return objects[index];
}

template<class T>
const T& Vector<T>::operator[](int index) const
{
    return objects[index];
}

template<class T>
bool Vector<T>::empty() const
{
    return size() == 0;
}

template<class T>
int Vector<T>::size() const
{
    return theSize;
}

template<class T>
int Vector<T>::capacity() const
{
    return theCapacity;
}

template<class T>
void Vector<T>::push_back(const T& x)
{
    if (theSize == theCapacity)
        reserve(theCapacity * 2 + 1);
    objects[theSize++] = x;
}

template<class T>
void Vector<T>::pop_back()
{
    theSize--;
}

template<class T>
const T& Vector<T>::back() const
{
    return objects[theSize - 1];
}

template<class T>
T* Vector<T>::begin()
{
    return &objects[0];
}

template<class T>
const T* Vector<T>::begin() const
{
    return &objects[0];
}

template<class T>
T* Vector<T>::end()
{
    return &objects[size() - 1];
}

template<class T>
const T* Vector<T>::end() const
{
    return &objects[size() - 1];
}

#endif