1.封装标准模板库(STL)---Vectors容器模板（已优化）;

#include <iostream>

using namespace std;

template <typename T>
class Myvector
{
private:
    T *first;  //指向堆区空间容器的首地址
    T *last;  //指向容器最后一个元素的下一个位置
    T *end;  //指向容器的最大位置

public:
    //构造函数
    Myvector(int size = 3)
    {
        first = new T[size];
        last =first;  //说明容器空
        end = first + size;
    }
    //析构函数
    ~Myvector()
    {
        delete [] first;
        first = nullptr;
        last = nullptr;
        end = nullptr;
    }

    //拷贝构造
    Myvector(const Myvector<T> &other)
    {
        int size = other.size();  //当前长度
        int max_size = other.max_size(); // 当前最大容量
        first = new T[max_size];

        memcpy(first,other.first,sizeof (T)*size);
        last = first + size;
        end = first + max_size;
    }

    //拷贝赋值
    Myvector &operator =(const Myvector<T> &other)
    {
        if(this != &other)
        {
            delete [] first;
            int size = other.size();
            int max_size = other.max_size();
            first = new T[max_size];   //新空间大小

            memcpy(first,other.first,sizeof (T)*size);
            last = first + size;
            end = first + max_size;
        }
        return *this;
    }

    //empty() 判空
    bool empty()
    {
        return last==first;
    }

    //full() 判满
    bool full()
    {
        return last==end;
    }

    //clear() 清空元素
    void clear()
    {
        last=first;
    }

    //size() 当前vector中元素的长度
    int size() const
    {
        return last-first;
    }

    //max_size() 当前vector的最大容量
    int max_size() const
    {
        return end-first;
    }


    //push_back() 尾插元素
    void push_back(const T elem)
    {
        if(full() == true)
        {
            cout<<"容器已满，2倍扩容后继续插入>>> "<<endl;
            expand();
        }
        *last = elem;
        last++;
    }

    //pop_back() 尾删元素
    void pop_back()
    {
        if(empty() == true)
            return;
        last--;
    }

    //T &at(int index) 查询元素
    T &at(int index)
    {
        if(index<0 || index>=size())
            throw string("访问越界！");  //异常处理
        return first[index];
    }

    //front() 返回首元素的引用
    T &front()
    {
        if(!empty())
            return *first;
        throw string("myvector空");
    }

    //back() 返回尾元素的引用
    T &back()
    {
        if(!empty())
            return *(last-1);
        throw string("myvector空");
    }

    //expand() 二倍扩容
    void expand()
    {
        int Msize = end - first;
        T *temp = new T[2*Msize];  //堆区申请一个2倍容器最大容量的空间
        memcpy(temp,first,sizeof(T)*Msize); //更新数据
        delete [] first;  //释放原空间
        first = temp;  //更新first指向

        last = first + Msize; //更新其他指针
        end = first + 2*Msize;
    }
    //遍历
    void Output()
    {
        for(int i=0; i<size(); i++)
        {
            cout<<first[i]<<" ";
        }
        cout<<endl;
    }

};

int main()
{
    Myvector<int> v1;

    if(v1.empty())          //判空
        cout<<"v1空"<<endl;
    else
        cout<<"v1不空"<<endl;

    for(int i=0; i<6; i++)  //尾插
    {
        int elem;
        cout<<"输入要插入的元素>>> ";
        cin>>elem;
        v1.push_back(elem);
    }
    v1.Output();       //遍历

    cout<<"v1.size= "<<v1.size()<<endl;

    v1.pop_back();      //尾删
    cout<<"尾删一个元素后>>> ";
    v1.Output();       //遍历

    cout<<"第一个元素>>> "<<v1.front()<<endl;  //首尾元素
    cout<<"最后一个元素>>> "<<v1.back()<<endl;

    cout<<"v1.at(0)>>> "<<v1.at(0)<<endl;  //查找元素
    cout<<"v1.at(1)>>> "<<v1.at(1)<<endl;
    cout<<endl;

    Myvector<int> v2(v1);    //拷贝构造
    cout<<"拷贝构造v2>>> ";
    v2.Output();

    Myvector<int> v3;    //拷贝赋值
    v3 = v1;
    cout<<"拷贝赋值v3>>> ";
    v3.Output();

    v1.clear();         //清空
    v2.clear();
    v3.clear();
    cout<<"v1v2v3清空后>>> ";
    v1.Output();       //遍历
    v2.Output();
    v3.Output();

    return 0;
}