inheritance - C++ Updating a variable in object of derived class via pointer -

i building linked list, nodes linked head. head derived node, head requires pointer last node. see comment @ top of code.

/*      base <= node <= node <= node  *       |                       ^  *       |    ptr last node   |  *       -------------------------  */  class node {  private:     node* prev;   public:     explicit node(node* parent) : prev(parent) {          node* foo_ptr = this;          while (foo_ptr->prev != 0) {             foo_ptr = foo_ptr->prev;         }          // foo_ptr points base, how can change base::last?     } };  class base : public node {  private:     node* last;  public:     base() : node(0), last(this) {} }; 

how can change change variable base::last when adding new node, example:

node* n = new base; new node(n);            // can node constructor update n->last? 

i thinking use virtual function update variable, according post: calling virtual functions inside constructors, no no not want it. there way of achieving type of linked list?

thanks...

http://coliru.stacked-crooked.com/a/213596aa1ffe7602

i added flag value can tell accessed base class:

#include <iostream>  class node {  private:     node* prev;   public:     inline void changebaselast(node* base);      explicit node(node* parent) : prev(parent) {          node* foo_ptr = this;          while (foo_ptr->prev != 0) {             foo_ptr = foo_ptr->prev;         }          // foo_ptr points base         // change base::last           changebaselast(foo_ptr);     }      int data; };  class base : public node {  private:     node* last;   public:     int flag;     base() : node(0), last(this), flag(0) {}  };  //here, can see change base_ptr 1. void node::changebaselast(node* base) {     base* base_ptr = static_cast<base*>(base);     base_ptr->flag=1; }  int main() {     node* n = new base;     new node(n);     std::cout << static_cast<base*>(n)->flag << std::endl; } 

if pull out part refers derived class , inline it, there should no problems this. notice, though, need define functions refer derived class after define derived class.

if you're sure last node base object, using static_cast<base*> may not bad.