C++ add a child node

Help Programming
1

Godot Version

4.3

Question

Switching to 4.3 with C++, some rules have changed. Now memnew and memdelete is forced.
Read about making a wrapper, but that doesn’t worked for create a node, then add it to a node as a child.

For now I only found this solution, but I really don’t like this way.

// in some.cpp
Button btn = memnew(Button);
somenode.add_child(btn);

// latter in other some2.cpp
for(size_t i {} ; i < get_children();i++){
    ...
    if (...) memdelete(child);
}
  • I would love to read, how do you handle this.
  • Also, the new upgrades with 4.3 with C++
1 Like
2

What is does memnew and memdel interface do? This will be defined somewhere in the Godot source.

There are potential easy ways to go about this if smart pointers are involved. If they are, your method above could be redundant and unnecessary.

3

I tried to use smart pointers with the last version, but godot forces you to use memnew or memdelete.

4

According to the memory.h interface memnew doesn’t use any special placement mechanism. So it ends up essentially being the same as new. So this would not effect smart pointers functionality and any need to call delete manually. Which would be the case if you use a memnew_placement call.

5

Btw i looked at the Godot source a little harder.

If you extend the Node class you shouldn’t need any special delete mechanism. If the notification_predelete is called it should do this fore you.

I think all you would need to do is call queue_free on yourself.

6

If you extend the Node class

Like this ?

// Some.hpp
class Some : public Node2D{
...
}

// OtherFile.hpp
auto Add() -> void {
   Some* d = memnew(Some);
   
   AParentNode.add_child(d);
}

auto Remove() -> void {
   for (size_t i ...
       memdelete( AParentNode.getchild(i) );
}
7

Do you want to preserve the parent node and remove just the children?

8

Yes, like shooting I would like to do:

  • Create a Node from code, then add it as a child to a node
Button btn
add_child(btn)
  • Create a custom node from code
MyButton btn
add_child(btn)

With the custom node I can use a wrapper with unique_ptr, but from a node from Godot, I cant.

9

Your example isn’t clear. But since you want to preserve the parent and remove the children i think the for loop is your best bet.

You could also say this if the nodes are part of the scene tree.

child.queue_free()

If you want to make a unique_ptr you could try this

unique_ptr<SomeNode> node (memnew(SomeNode));

But this should probably be avoided as Godot doesn’t include much of the standard library. And you may want to modify the default_deleter behavior in some cases anyway.

10

Btw someone is proposing a function.

11

Nop, that doesn’t work:

std::unique_ptr<Button> btn ( memnew(Button) );
add_child(btn.get( )); // free(): invalid pointer

add_child(btn); // No compile

Also tried

template <class T>
struct GodotObjectDeleter {
	void operator( )(T* obj) const { memdelete(obj); };
};

template <class T>
using gd_ptr = std::unique_ptr<T, GodotObjectDeleter<T>>;

template <class T>
static gd_ptr<T> make_go( ) {
	return gd_ptr<T>(memnew(T), GodotObjectDeleter<T>( ));
}
12

The problem with using unique pointer is that it shouldn’t be shared, and when passing ownership should use the move syntax. Once your unique pointers goes out of scope it will delete the memory and Godot may try and access the raw pointer and free it later. Hence the invalid free error.

Like i said you probably should avoid it anyway.