自己實現一個STL的vector容器

封裝了vector的數據結構，和push_back(),capacity(),size()方法，內嵌了iterator迭代器類

#include <iostream>
// #include <vector>
using namespace std;
namespace miniSTL{
template<typename T>
class vector{
    T* _data;
    size_t _size;// 元素個數
    size_t _capacity;// 容量
public:
    vector():_data(NULL),_size(0),_capacity(0){}
    ~vector(){delete [] _data;}
    // 拷貝構造函數
    // 賦值運算符重載函數
    void push_back(const T& val){
        ++_size;
        if(NULL == _data){
            ++_capacity;
            _data = new T[_capacity];
        }else{
            if(_size>_capacity){ // 擴容
                _capacity*=2;
                T* temp = new T[_capacity];
                for(int i=0;i<_size-1;++i){
                    temp[i] = _data[i];
                }
                delete [] _data;
                _data = temp;
            }
        }
        _data[_size-1] = val;
    }
    int size()const{return _size;}
    int capacity()const{return _capacity;}
    T& operator[](int index){
        return _data[index];
    }
    const T& operator[](int index)const{
        return _data[index];
    }

    // 嵌套類:類中定義的類
    class iterator{
        T* _p;
    public:
        iterator(T* p):_p(p){}
        T& operator*(){return *_p;}
        T* operator->(){return _p;}
        //iterator operator++(){
        //    ++_p;
        //    return *this;
        //}
        bool operator==(const iterator& it)const{
            return _p == it._p;
        }
        bool operator!=(const iterator& it)const{
            return _p != it._p;
            // return !(*this == it);
        }
        // 所有操作符除了前綴後綴還有複合賦值+= -= *=之外，不會改變原來下變量值
        iterator operator+(int n)const{
            return iterator(_p+n);
        }
        iterator operator-(int n)const{
            return iterator(_p-n);
        }
        iterator operator++(){
            return iterator(++_p);
        }
        iterator operator++(int){
            iterator tmp(_p);
            ++_p;
            return tmp;
        }
        iterator operator--(){
            return iterator(--_p);
        }
        iterator operator--(int){
            // iterator tmp(_p);
            iterator tmp(*this);
            --_p;
            return tmp;
        }
    };

    iterator begin(){
        return iterator(_data);
    }
    iterator end(){
        return iterator(_data+_size);
    }
};
}

using namespace miniSTL;
class Student{
public:
    string name;
    int age;
};
ostream& operator<<(ostream& os,const Student& s){
    return os << s.name << "," << s.age;
}

int main(){
    vector<int> vec;
    cout << sizeof(vec) << endl;
    for(int i=0;i<20;++i){
        vec.push_back(i);
        cout << "size:" << vec.size() << ",capacity:" << vec.capacity() << endl;
    }
    cout << sizeof(vec) << endl;

    /*
    for(int i=0;i<vec.size();++i){
        cout << vec[i] << " ";
    }
    cout << endl;
    */
    vector<int>::iterator it = vec.begin();
    while(it != vec.end()){
        cout << *it << endl;
        ++it;
    }
    cout << endl;
    for(auto n:vec){
        cout << n << " ";
    }
    cout << endl;
    vector<Student> vec1;
    vec1.push_back({"張三",21});
    vec1.push_back({"李四",23});
    vec1.push_back({"王五",20});
    
    vector<Student>::iterator it1 = vec1.begin();
    cout << (*(it1+2)).name << endl;
    while(it1 != vec1.end()){
        // cout << it1->name << "," << it1->age << endl;
        // ++it1;
        cout << *it1++ << endl;
    }
    cout << endl;

//    int  n = 10；
    // n+1
    //  ++n //
    //  n++ // 
}