How do I get the value of this void* back?

Question

I have a void pointer of which I can set the value just fine (at least I think I did it right). But when I try to get the value of what is stored there, all I get nothing back. Doesn't matter if the void* points to a string or int or anything else. What am I missing here?

class Vertex2{
public:
    int _id;

    void *_data;

    template<typename T>
    T getData() {
        T *value = (T*)_data;
        return *value;
    }

    template <typename T>
    void setData(T data) {
        _data  = &data;
    }
};

Answer 1

void setData(T data) receives data by value.

Setting a pointer to data therefore is only valid for the lifetime of that function call.

After that, the pointer dangles, and dereference behaviour is undefined.

Answer 2

template <typename T>
void setData(T data) {
    _data  = &data;
}

let's check what's going on here. You store a pointer to a local variable (method argument actually). Right after you leave the method the local var is destroyed and its memory is free to be reused. Now your void* points to the same memory address but the memory can contain anything.