为什么都不调用Copy构造函数或赋值运算符？

Question

  

有人可以在下面的示例代码中进行解释：

     

  

1. 为什么既不调用构造函数也不调用赋值运算符。

  

2. 为什么在类的+运算符中创建的对象在运算符调用结束后没有被破坏，而是分配给了c3。

  

     

示例代码：

#include<iostream>
using namespace std;

class Complex {
private:
    int real, imag;
public:
    Complex(int r = 0, int i =0) {cout<<"Constructor"<<endl; real = r; imag = i;}

    Complex(Complex const &obj) {
        cout<<"Copy Constructor"<<endl;
        real = obj.real;
        imag = obj.imag;
    }

    ~Complex() {
        cout<<"Destructor"<<endl;
    }

    Complex operator + (Complex const &obj) {
        cout<<"Operator +"<<endl;
        Complex res;
        res.real = real + obj.real;
        res.imag = imag + obj.imag;
        return res;
    }

    void operator = (Complex const &obj)
    {
        cout<<"Operator ="<<endl;
    }

    void print() { cout << real << " + i" << imag << endl; }
};

int main()
{
    Complex c1(10, 5), c2(2, 4);
    Complex c3 = c1 + c2;
    c3.print();
}

输出：

    Constructor
    Constructor
    Operator +
    Constructor
    12 + i9
    Destructor
    Destructor
    Destructor