#include <bits/stdc  .h>
using namespace std;
class node{
public:
    int data;
    vector<node*> children;
};

node* createTree(const vector<int>& nums){
    stack<node*> st;
    node *root = new node(nums[0]);
    st.push(root);
    for(int i=1;i<nums.size();i  ){
        if(nums[i]==-1){
            st.pop();
        }else{
            node *n = new node(nums[i]);
            st.top()->children.push_back(n);
            st.push(n);
        }
    }
    return root;
}
void display(node& *root){
    cout << root->data << "->";
    for(node& *child:root->children)
        cout << child->data << " ";
    cout <<"\n";
    for(node& *child:root->children)
        display(child);
}
int main(){
    #ifndef ONLINE_JUDGE
        freopen("input.txt","r",stdin);
        freopen("output.txt","w",stdout);
        freopen("error.txt","w",stderr);
    #endif
    vector<int> nums = {10,20,-1,30,50,-1,60,-1,-1,4,-1,-1};
    node *root = createTree(nums);
    display(root);
    return 0;
}

<source>:25:20: error: 'root' declared as a pointer to a reference of type 'node &'
void display(node& *root){
                   ^
<source>:27:15: error: 'child' declared as a pointer to a reference of type 'node &'
    for(node& *child:root->children)
              ^
<source>:30:15: error: 'child' declared as a pointer to a reference of type 'node &'
    for(node& *child:root->children)
              ^

Here i am trying to implement a generic tree and when i try to compile the program i get an an error message saying that in display function i cannot declare a pointer to node&. I know that we cannot create a pointer to a reference since references do not have separate physical address, for example something like int* &b would not be permissible but int& *b would be permissible.Since here i have used node& *, i should not have got any error.Then why the program above is giving error?

CodePudding user response：

You're correct about the pointer to a reference vs reference to a pointer but got the syntax wrong.

Pointer to a reference is declared as: type&* obj
Reference to a pointer is declared as: type*& obj

Thus, the way that you think is "wrong", turns out to be correct:

void display(node*& root)

Edit: It's easier to imagine this way: (type*)& obj vs (type&)* obj