c++ - Initialize a reference - warning C4355: 'this' : used in base member initializer list

Question

class A;

class B {
public:
    B(A& a) : a(a) {}
private:
    A& a;
};

/* Method 1 */
/* warning C4355: 'this' : used in base member initializer list */
/*
class A {
public:
    A() : b(*this) {}

private:
    B b;
};
*/

/* Method 2 */
/* But I need to manually perform memory dellocation. */
class A {
public:
    A() { b = new B(*this); }
    ~A() { delete b; }

private:
    B* b;
};

int main() {
}

Currently, when I try to initialize the reference in B, I am using Method 1. However, Method 1 will flag me warning which is understandable.

Hence, I have to fall back using Method 2, by using dynamic memory allocation.

Is there any better way I can use, without the need of manual memory allocation/ dellocation (OK. I know smart pointer)?

I prefer Method 1, just that I am not comfortable with the warning.

Answer 1

Note this is a warning (so it is dangerous not illegal).

What the compiler is worried about is that you are passing a pointer for an object that has not been fully initialized. Thus if the pointer is used in the B class constructor you are in undefined behavior.

So if you do use this the only thing you can do is assign the pointer to a member variable (reference or pointer). But note be careful of the assignment to a variable as you may invoke an implicit cast (I am not sure if that is actually a problem but the RTTI is not available until the object is fully formed).

What are you trying to achieve by storing the reference?