How to implement a class member which is a instance of the class I define: Get "wrong parameters count"

[Rouge Mouta]

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

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

Hi community,

I'm trying to have a class member which is a instance of the class I define.

(In this code, trying to have a member "A a" in the class "B")

When I compile it, result is:

'A' - wrong parameters count

at second to the last line.

Q1. Is it possible to achieve what I'm trying here?

if (Q1 == true)

Q2. How should I implement?

else

Q3. Any workaround you suggest?

Thanks.

[Dominik Egert]

The default consteuctor of B is wrong.

Remove a(A())

[Carl Schreiber]

I recommend you what I wrote here: https://www.mql5.com/en/forum/376954#comment_24432264

It's a lot faster than waiting here for an answer.

[Rouge Mouta]

Thanks. That's a solution.

I prefer to use initializer list so I wrote this way.

If I removed the A() and just leave a() empty, that seems fix the problem in my preferred way.

I don't need to call a constructor in the initializer list. All it needs is params of the constructor.

public:
        B(): a() {};

My question is now clearer.

How to use member initializer list correctly.

[Rouge Mouta]

Carl Schreiber #:

I recommend you what I wrote here: https://www.mql5.com/en/forum/376954#comment_24432264

It's a lot faster than waiting here for an answer.

You are right. There is an answer in the link.

https://www.mql5.com/en/docs/basis/types/classes#initialization_list

Thanks!

[Dominik Egert]

As far as I am aware, there is no need for explicit calling the default constructor of a member in the class default constructor, as it is implicitly called at definition of the "containing" class.

But I would have to verify this by code to be certain.

So my assumption is, when constructing (defining) class B, the member a gets defined and thus calls it's default constructor.