#include <cstdio>
#include <memory>
#include <utility>

template<typename T>
class myVector
{
public:
    // 默认构造函数，创建一个大小为 0 的 vector
    myVector() : _start(nullptr), _finish(nullptr), _endOfStorage(nullptr) {}

    // 创建一个大小为 n，默认值为 T 的 vector
    myVector(size_t n, const T& value = T())
        : _start(nullptr), _finish(nullptr), _endOfStorage(nullptr) {
        reserve(n);
        while (n--) {
            push_back(value);
        }
    }
    ~myVector() {
        if (_start) {
            delete[] _start;
            _start = nullptr;
            _finish = nullptr;
            _endOfStorage = nullptr;
        }
    }

    void        reserve(size_t n); // 申请空间
    void        resize(size_t n, const T& value = T()); // 重新设置 vector 大小
    void        push_back(T &&value); // 插入一个右值
    void        push_back(const T& value); // 插入一个变量

    // vector 总的可用空间
    size_t      capacity() const { return _endOfStorage - _start; }
    size_t      size() const { return _finish - _start; }

    // 重载 [] 符号
    T&              operator[](size_t pos) { return _start[pos]; }
    myVector<T>&    operator=(const myVector<T>& v);

private:
    T*          _start; // 数组首地址
    T*          _finish; // 最后一个元素的下一个地址
    T*          _endOfStorage; // 空间的尾地址
};

template<typename T>
inline void myVector<T>::reserve(size_t n)
{
    if (n > capacity()) {
        size_t sz = size();
        T* arr = new T[n];
        if (_start) {
            memcpy(arr, _start, sizeof(T) * sz);
            delete[] _start;
        }
        _start = arr;
        _finish = _start + sz;
        _endOfStorage = _start + n;
    }
}

template<typename T>
inline void myVector<T>::resize(size_t n, const T &value)
{
    if (n > capacity())
        reserve(n);

    if (n > size()) {
        while (_finish != _start + n) {
            *_finish = value;
            ++_finish;
        }
    }
    _finish = _start + n;
}

template<typename T>
inline void myVector<T>::push_back(T&& value)
{
    if (_finish == _endOfStorage) {
        size_t sz = _endOfStorage == nullptr ? 1 : 2 * capacity();
        reserve(sz);
    }
    *_finish = value;
    ++_finish;
}

template<typename T>
inline void myVector<T>::push_back(const T &value)
{
    if (_finish == _endOfStorage) {
        size_t sz = _endOfStorage == nullptr ? 1 : 2 * capacity();
        reserve(sz);
    }
    *_finish = value;
    ++_finish;
}

template<typename T>
inline myVector<T>& myVector<T>::operator=(const myVector<T>& v)
{
    if (this != &v) {
        delete[] _start;
        size_t n = v.capacity();
        size_t sz = v.size();
        _start = new T[n];
        memcpy(_start, v._start, sizeof(T) * sz);
        _finish = _start + sz;
        _endOfStorage = _start + n;
    }
    return *this;
}

测试：

int main()
{
    int a = 2;
    myVector vec(10, a);

    for (int j = 0; j < 10; ++j) {
        vec.push_back(j);
    }

    myVector<int> vec1;
    vec1 = vec;
    for (unsigned i = 0; i < vec1.size(); ++i) {
        cout << vec1[i] << endl;
    }
    return 0;
}