C++ - 奇怪的代码输出

Question

此代码：

class A {
public:
    int _a;
    A():_a(0) { cout << "A default - ctor, ";}
    A(int i):_a(i) { cout << "A int - ctor, ";}
    operator int() { cout << "A int - operator, "; return 33;}
    virtual ~A() { cout << "A dtor, ";}
};
int main() {
    A* a = new A(99);
    cout << *a << endl;
    return 0;
}

我希望输出是：一个 int-operator, A int-ctor, 33

但真正的输出是： A int-ctor, A int-operator, 33

Answer 1

首先你调用"new A(99)" ，它调用"A(int i)" ，它打印"A int - ctor, " 。

以下行调用"cout << *a" ，它调用"operator int()" ，它打印"A int - operator, " 。

然后该行以"cout << [result] << endl" ，它打印结果 (33) 和换行符。

所以"A int - ctor, " + "A int - operator, " + "33" + "endl"是"A int - ctor, A int - operator, 33" 。