C++ 奇怪的构造函数行为

Can anybody explain to me the difference between Complex a; and Complex b();?

#include<iostream>

class Complex
{
public:

    Complex()
    {
        std::cout << "Complex Constructor 1" << std::endl;
    }

    Complex(float re, float im)
    {
        std::cout << "Complex Constructor 2" << std::endl;
    }

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

int main()
{
    Complex a;
    std::cout << "--------------------------" << std::endl;
    Complex b();
    std::cout << "--------------------------" << std::endl;
    Complex c(0,0);
    std::cout << "--------------------------" << std::endl;

    return 0;
}

输出:

Complex Constructor 1
--------------------------
--------------------------
Complex Constructor 2
--------------------------
Complex Destructor
Complex Destructor

如您所见，Complex a; 确实调用了它的默认构造函数，Complex b(); 没有，Complex c(0,0); 调用重载的构造函数.

Complex b{};