Why does recursion appear in QVector?

John Van

In this code, recursion appears in QVector, but not in std::vector.

struct TreeNode
{
    QString name;
    QVector<TreeNode> nodes;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    TreeNode n0{ "n0" };
    n0.nodes.push_back(n0);
    n0.nodes[0].nodes.push_back(n0);

}

&n0 0x0000002fa1bcf6e8 {name=n0 nodes={ size = 1 } }
&n0.nodes[0] 0x0000013ce627d2f8 {name=n0 nodes={ size = 1 } }
&n0.nodes[0].nodes[0] 0x0000013ce627e878 {name=n0 nodes={ size = 1 } }
&n0.nodes[0].nodes[0].nodes[0] 0x0000013ce627d2f8 {name=n0 nodes={ size = 1 } }
&n0.nodes[0].nodes[0].nodes[0].nodes[0] 0x0000013ce627e878 {name=n0 nodes={ size = 1 } }

J.Hilk

That's surprising, both should show recursive behaviour. Because you modify the nodes wich would trigger a copy of the vector element.
~
Actually std::vector has no implizit sharing, it does the copy directly. Probably the reason why you see different behaviour.

jsulm

@John-Van What recursion do you mean? This code runs just fine. Why you're adding n0 into its own nodes vector and then again into nodes[0] is another question. Is there a reason to do this?

J.Hilk

That's surprising, both should show recursive behaviour. Because you modify the nodes wich would trigger a copy of the vector element.
~
Actually std::vector has no implizit sharing, it does the copy directly. Probably the reason why you see different behaviour.