Class member of the same class?

Question

Is it possible to make a child member of the same class in C++? Something like

class A
{
public:
  int i;
  A child;
};

Thanks in advance.

score 5 · Accepted Answer · answered Nov 18 '13 at 13:46

5

This requires the infinite type, which is not possible in C++.

You need extra indirection, for example through a pointer:

#include <memory>

class A {
public:
    int i;
    std::unique_ptr<A> child;
};

answered Nov 18 '13 at 13:46

Worth mentioning also the possibility of `std::shared_ptr` and `std::weak_ptr`, as well as a bare pointer or a reference, which might still be relevant in some cases. See also: https://stackoverflow.com/questions/63365537/c-instance-of-same-class/63365597#63365597 – Amir Kirsh Aug 12 '20 at 10:06

score 1 · Answer 2 · answered Nov 18 '13 at 13:47

1

You cant have a member object of the same type ( otherwise the class would go infinitely large) but your class can have a pointer that points to an object of the same type. i.e,

class A
{
public:
 int i;
 A *child;
};

is possible.

answered Nov 18 '13 at 13:47

jester

3,491
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score 1 · Answer 3 · answered Nov 18 '13 at 13:48

1

You can do it only for static data members because it is allowed that declarations of static data members had incomplete types. You may not do the same with non-static data members. You can only define them as pointers to the class itself.

answered Nov 18 '13 at 13:48

Vlad from Moscow

301,070
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score 0 · Answer 4 · answered Nov 18 '13 at 13:46

Directly - no. How big would that structure be?

But there is another way, you can contain a pointer to your class:

class A
{
public:
    int i;
    A * child;
};

If you want to implement it more clearly, you may use std::unique_ptr or std::shared_ptr instead of C-style pointer, depending on your needs.

But everything depends on what you want to achieve. If you're implementing your own data structure - such as list, tree etc., this is a good approach. But otherwise I'd think, if such dependency is really required and if such solution isn't some kind of design flaw.

Class member of the same class?

4 Answers4