How to avoid calling the constructor of parent class?

[Eugen Funk]

Hi, I have the problem that when an object of the child class is created, the constructor of the parent class is called without notice.

class ClassA {
  public:
  ClassA(){
    Print("ClassA Constructor");
  };
};

class ClassB:public ClassA {
  public:
  ClassB(){
    Print("ClasB");
  }

};


int OnInit()
{
  ClassB* cb = new ClassB();


  return(INIT_SUCCEEDED);
}

Output:

🤔

[Dominik Egert]

Eugen Funk:

Hi, I have the problem that when an object of the child class is created, the constructor of the parent class is called without notice.

Output:

🤔

Practically not possible. What you can do is this:

class A
{
    A() = delete;
};

class B : public A
{
    B()
    {};
};

Or this:

class A
{
};

class B : public A
{
    B()
    {};
};

But why???

EDIT:

Try to compile it and see what happens....

[Eugen Funk]

nah, because the classB has other tasks than classA ... 
Ok, i changed the structure little bit the stuff works as I need it - but strange. C++ and other languages are different.

Thank you!

[Alain Verleyen]

Eugen Funk:

Hi, I have the problem that when an object of the child class is created, the constructor of the parent class is called without notice.

Output:

🤔

What a bad idea !

The constructor of A NEEDS to be called.

[Dominik Egert]

Alain Verleyen #:

What a bad idea !

The constructor of A NEEDS to be called.

Of course, and omitting it in A will just create an implicit constructor...

EDIT:

I would say, there is a fundamental design flaw, if you need to do something like that.

[Alain Verleyen]

Dominik Egert #:
Of course, and omitting it in A will just create an implicit constructor...

And the "delete" version doesn't compile.

[Alain Verleyen]

Eugen Funk #:

nah, because the classB has other tasks than classA ... 
Ok, i changed the structure little bit the stuff works as I need it - but strange. C++ and other languages are different.

Thank you!

What language allows to create a subclass which doesn't call the parent constructor ?

[Dominik Egert]

Alain Verleyen #:
And the "delete" version doesn't compile.

Of course not...

[Eugen Funk]

Alain Verleyen #:
What language allows to create a subclass which doesn't call the parent constructor ?

C++, Python, ... You usually need to call it explicitly via super(),

ClassB(int x):ClassA(x){...}

[Alain Verleyen]

Eugen Funk #:

C++, Python, ... You usually need to call it explicitly via super(),

C++ is similar to MQL in that regards.

Even if C++ allow to somehow to not call the base constructor (as far as I know it's done implicitly if not explicitly), it's really a strange requirement. I can't imagine something else that a bad design.

[Dominik Egert]

Eugen Funk #:

C++, Python, ... You usually need to call it explicitly via super(),

as reference, take a look here:

https://www.ibm.com/docs/en/zos/3.1.0?topic=only-initialization-base-classes-members-c

It's C++11