c++ - 表达式 MyClass a = b + c 是复制初始化吗？

Question

我知道像 MyClass a = b 这样的表达式是一个复制初始化，它会调用复制构造函数。

MyClass a = b + c 呢？

我试过了。在visual studio 2015中，表达式似乎不是复制初始化，也不是复制赋值。那是什么？

下面是我测试的代码:

class MyClass
{
public:
    MyClass()
    {
        cout << "default constructor has been called!" << endl;
    }
    MyClass(const MyClass& cls)
    {
        cout << "copy constructor has been called!" << endl;
    }
    MyClass operator+(const MyClass& cls) const
    {
        cout << "operator + has been called!" << endl;
        return MyClass();
    }
    MyClass& operator=(const MyClass& cls)
    {
        cout << "operator = has been called!" << endl;
        return *this;
    }
};

int main()
{
    MyClass b, c;
    MyClass a = b + c;
    return 0;
}

输出是

default constructor has been called!
default constructor has been called! 
operator + has been called!
default constructor has been called! 

Answer 1

复制构造函数may be elided在这种情况下。