this指针写入访问权限冲突

Question

运行结果及报错内容

#include <iostream>
using namespace std;
class Vector {
private:
    int* nums;
    int len;
public:
    Vector(int = 1);
    Vector(int*, int);
    Vector(const Vector&);
    ~Vector();
    int& operator [](int i) const;
    Vector& operator=(const Vector&);
    friend Vector operator +(const Vector&, const Vector&);
    friend Vector operator -(const Vector&, const Vector&);
    friend double operator *(const Vector&, const Vector&);
    friend ostream& operator <<(ostream& output, const Vector&);
    friend istream& operator >>(istream& input, Vector&);
};
Vector::Vector(int size) {
    nums = new int[size];
    for (int i = 0; i < size; i++) nums[i] = 0;
    len = size;
}
Vector::Vector(int* temp, int size) {
    len = size;
    for (int i = 0; i < size; i++) nums[i] = temp[i];//此处报错
}
Vector::Vector(const Vector& temp) {
    len = temp.len;
    for (int i = 0; i < len; i++) nums[i] = temp.nums[i];
}
Vector::~Vector() {
    len = 0;
    delete[] nums;
}
int& Vector::operator[](int size)const {
    return nums[size];
}
Vector& Vector::operator=(const Vector& temp) {
    for (int i = 0; i < len; i++) nums[i] = temp.nums[i];
    return *this;
}
Vector operator +(const Vector& A, const Vector& B) {
    int size = A.len;
    int* temp = new int[size];
    for (int i = 0; i < A.len; i++) temp[i] = A.nums[i] + B.nums[i];
    return Vector(temp, size);
}
Vector operator -(const Vector& A, const Vector& B) {
    int size = A.len;
    int* temp = new int[size];
    for (int i = 0; i < size; i++) temp[i] = A.nums[i] - B.nums[i];
    return Vector(temp, size);
}
double operator *(const Vector& A, const Vector& B) {
    int ans = 0;
    for (int i = 0; i < A.len; i++) ans += A.nums[i]*B.nums[i];
    return ans;
}
ostream& operator <<(ostream& output, const Vector& A) {
    for (int i = 0; i < A.len; i++) output << A[i] << " ";
    output << endl;
    return output;
}
istream& operator >>(istream& input, Vector& A) {
    for (int i = 0; i < A.len; i++) {
        input >> A.nums[i];
    }
    return input;
}
int main() {
    int len; cout << "输入向量维数: "; cin >> len;
    Vector A(len), B(len), C(len), D(len);
    cin >> A >> B;
    cout << A << B;
    C = A + B;
    cout << "执行A+B后,向量C为: " << C;
    C = A - B;
    cout << "执行A-B后,向量C为: " << C;
    cout << "执行A*B后,结果为: " << A * B;
}

代码如上
报错：
引发了异常: 写入访问权限冲突。
this->nums 是 0x191113A。
运行结果：
输入向量维数: 2
1 2
2 1
1 2
2 1
执行A+B后,向量C为: 3 3
不知如何修改，求解

Answer 1

27行肯定不行啊，构造时，nums指针还没有分配空间呢，你得跟上一个构造函数一样，增加nums = new int[size];