C++ 将对象保存在列表中以便以后重用

Question

Suppose I own a list of edges saved inside a vector like:

typedef struct edge
{
  int v;
  size_t start;
  size_t end;
}e;

typedef vector<list<e>> adj_list;
adj_list tree;

I have to do logic on this tree object, but the logic is too complicated to do it in place (constricted to not recurse). I need an extra data structure to handle each node. As a simple example, lets consider incrementing each edge's v value:

list<e> aux;
  aux.insert(aux.begin(), tree[0].begin(), tree[0].end());
  while (!aux.empty())
    {
      e& now = aux.front();
      aux.pop_front();
      now.v++;
      aux.insert(aux.begin(), tree[now.v].begin(), tree[now.v].end());
      
    }

The problem in doing this is that the changes made to the now variable does not reflect the value in tree . I need a list(can be any list(vector,linked,queue,stack) that has an empty() boolean like Dijkstra) ds to handle my edge objects in tree . Is there an elegant way to do this? Can I use a list of iterators? I'm specifically asking an "elegant" approach in hopes that it does not involve pointers.

Answer 1

As discussed in the comments, the solution is to store iterators instead of copies, eg:

list<list<e>::iterator> aux;
aux.insert(aux.begin(), tree[0].begin(), tree[0].end());
while (!aux.empty())
{
  e& now = *(aux.front());
  aux.pop_front();
  now.v++;
  aux.insert(aux.begin(), tree[now.v].begin(), tree[now.v].end());    
}

This works only if you can guarantee that nothing will invalidate the stored iterators, such as certain operations on tree could do.

As pointed out by n. 'pronouns' m. , iterators can be considered as "generalized pointers", so many problems that regular pointers have also apply to iterators.

Another (slightly safer) approach would be to store std::shared_ptr s in the inner list of tree - then you can simply store another std::shared_ptr to the same object in aux which makes sure that the object cannot be accidentally deleted while it is still being referenced