I have been trying to debug this for a while now without any luck. I was hoping to get some help here. Apologies if my question isn't relevant or something, I'm new.
So basically what I have is:
#include <iostream>
template<typename T> class Node {
using NodePtr = std::shared_ptr<Node<T>>;
private:
Node() {}
T value{};
NodePtr parent;
NodePtr child;
public:
Node(const T& value) : value{ value } {}
Node(const T& value, NodePtr child) : Node(value)
{
this->child = child;
if (child != NULL)
{
//problem here?
child->parent = NodePtr(this);
/*The equivalent in C# works perfectly fine:*/
/*this.child = child;
if(child != null) {
child.parent = this;
}*/
}
}
const T& Value() const { return value; }
T& ValueRef() const { return value; }
NodePtr Parent() const { return parent; }
NodePtr Child() const { return child; }
};
template<typename T> std::ostream& operator<<(std::ostream& stream, const Node<T>& node) {
stream << "{" << node.Value() << "}";
return stream;
}
int main()
{
Node<int> n{ 5, std::make_shared<Node<int>>(3) };
std::cout << n;
}
I can implement this easily without using smart pointers, but I'm trying to learn them so there's that.
The assertion that is failing: "is_block_type_valid(header->_block_use)"
Any help would be appreciated, thank you.
CodePudding user response:
There are a few problems. First, if you want to get a shared_ptr from this, you have to inherit from std::enable_shared_from_this:
template<typename T> class Node : std::enable_shared_from_this<Node<T>> {
// ...
The main problem is that there is a shared_ptr referencing a shared_ptr (the parent to the child, vice-versa). However, shared_ptr are only reference-counted. Take a look at the program below:
#include <iostream>
#include <memory>
struct A;
struct B{
std::shared_ptr<A> sp;
~B(){ std::cout << "B destroyed\n"; }
};
struct A{
std::shared_ptr<B> sp;
~A(){ std::cout << "A destroyed\n"; }
};
int main(){
std::shared_ptr<B> b{};
std::shared_ptr<A> a {b->sp};
b = a->sp;
}
The output is blank! Here is a link to the above program.
To fix, do two additional things: one, change child->parent = NodePtr(this);
to the following:
child->parent = this->weak_from_this();
Also, change the type of parent
to std::weak_ptr<Node<T>>
.
std::weak_ptr
is used with problems like this. It doesn't influence the reference count of the std::shared_ptr
For more information, go here.
P.S. the error about the is_block_type was caused by shared_ptr, probably because you tried to get a shared_ptr from a raw ptr. Read more about std::shared_ptr here.