Memory leak despite using unique_ptr

Question

I have a constructor for a class that initializes a unique_ptr inside of that class with a value passed to it. For some reason, valgrind complains about a memory leak:

22,080 (24 direct, 22,056 indirect) bytes in 1 blocks are definitely lost in loss record 6 of 6
   at 0x4C2C7A7: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x4A64FB: VectorBasedNodeOrder::VectorBasedNodeOrder(VectorBasedNodeOrder const&) (VectorBasedNodeOrder.cpp:33)
   /* snip more trace */

This is the allegedly offending code, stripped of all the irrelevant stuff:

class VectorBasedNodeOrder : public NodeOrder
{
public:
    VectorBasedNodeOrder(const VectorBasedNodeOrder& order);
protected:
    std::unique_ptr<std::vector<Node*>> orderedNodes;
}

VectorBasedNodeOrder::VectorBasedNodeOrder(const VectorBasedNodeOrder& order):
NodeOrder(order),
orderedNodes(unique_ptr<std::vector<Node*>>(
    new std::vector<Node*>(*(order.orderedNodes)))) // <-- line 33
{
}

Can you please explain why and how the memory leak occurs?

Answer 1

Based on your comment that the raw Node pointers are managed elsewhere and not the problem I'm going to take a wild stab that NodeOrder or a further parent doesn't have a virtual destructor, and when your VectorBasedNodeOrder is destroyed polymorphically by base class pointer, the child destructor is never called, resulting in the unique_ptr never being destructed.