如何在cpp中重载操作符+=？

#include <iostream>

class Vector2D {
private:
    double x;
    double y;

public:
    // 构造函数
    Vector2D(double x = 0.0, double y = 0.0) : x(x), y(y) {}

    // 成员函数重载 += 操作符
    Vector2D& operator+=(const Vector2D& other) {
        x += other.x;
        y += other.y;
        return *this;
    }

    // 友元函数重载 << 操作符以方便输出
    friend std::ostream& operator<<(std::ostream& os, const Vector2D& vec);
};

// 实现 << 操作符重载
std::ostream& operator<<(std::ostream& os, const Vector2D& vec) {
    os << "(" << vec.x << ", " << vec.y << ")";
    return os;
}

int main() {
    Vector2D v1(1.0, 2.0);
    Vector2D v2(3.0, 4.0);

    v1 += v2; // 使用重载的 += 操作符

    std::cout << "v1 after += operation: " << v1 << std::endl; // 输出: (4, 6)

    return 0;
}