实现vector里函数功能：

#include <iostream>

using namespace std;

template <typename T>
class myvector
{
private:
    T * first;
    T * last;
    T * end;
public:
    //无参构造
    //myvector() {cout<<"无参构造"<<endl;}

    //有参构造
    myvector():first(nullptr),last(nullptr),end(nullptr)
    {
        cout<<"有参构造"<<endl;
    }

    //析构函数
    ~myvector()
    {
        delete []first;
        cout<<"析构函数"<<endl;
    }

    //拷贝构造
    myvector(const myvector &other)
    {
        int length = other.size();
        first = new T[length];
        last = first + length;
        end = last;
        for(int i=0;i<length;i++)
        {
            first[i]=other.first[i];
        }
        cout<<"拷贝构造"<<endl;
    }

    //拷贝赋值
    myvector &operator=(const myvector &other)
    {
        if(this != &other)      //避免自己给自己赋值
        {
            int length = other.size();
            first = new T[length];
            last = first + length;
            end = last;
            for(int i=0;i<length;i++)
            {
                first[i]=other.first[i];
            }
        }
        cout<<"拷贝赋值"<<endl;
        return *this;
    }

    //获取指定下标的元素
    T &at(int index)
    {
        return first[index];
    }

    //判断容器是否为空
    bool empty()
    {
        return first==last;
    }

    //判断容器是否满
    bool full()
    {
        return last==end;
    }

    //返回第一个元素
    T &front()
    {
        return *first;
    }

    //返回最后一个元素
    T &back()
    {
        return *(last-1);
    }

    //返回容器大小
    int size()
    {
        return (last-first);
    }

    //清空容器
    void clear()
    {
        last=first;
    }

    //二倍扩容
    void expand()
    {
        int length = size();
        int newvector = length*2;   //扩容
        T *newfirst = new T[newvector]; //创建新的连续空间
        T *newlast = newfirst + length;
        T *newend = newfirst + newvector;
        for(int i=0;i<length;i++)   //循环赋值
        {
            newfirst[i] = first[i];
        }
        delete []first;     //释放之前的空间
        first = newfirst;   //改变指针
        last = newlast;
        end = newend;
    }

    //尾插
    void push_back(const T &key)
    {
        if(full())
        {
            expand();
            cout<<"已经二倍扩容，可以插入"<<endl;
        }
        *last = key;
        last++;

        if(last>end)
        {
            end = last;
        }
    }

    //尾删
    void pop_back()
    {
        if(empty())
        {
            cout<<"删除失败"<<endl;
            return;
        }
        last--;
        cout<<"删除成功"<<endl;
    }
};

int main()
{
    myvector<int> vec;
    //插入
    vec.push_back(1);
    vec.push_back(4);
    vec.push_back(9);

    //输出
    for(int i=0;i<vec.size();i++)
    {
        cout<<vec.at(i)<<"  ";
    }
    cout<<endl;

    //删除
    vec.pop_back();

    for(int i=0;i<vec.size();i++)
    {
        cout<<vec.at(i)<<"  ";
    }
    cout<<endl;

    return 0;
}

思维导图：