C ++中的二叉树

Question

I'm trying to implement a binary tree in C++ and transverse it in a root-left-right manner. After I add all the nodes I get a crash at this line:

cout << r->st->st->info << endl; //trying to print root->left->left->info

My RSD function doesn't print anything. Also, I would appreciate any Visual Studio tutorials on how to use the debugger. Thank you.

#include<iostream>
using namespace std;

struct Nod{
    int info;
    Nod *st, *dr;
};

int read_tree(Nod *r)
{
    int info;
    cout << "Info: "; cin >> info;
    if (info!=0)
    {
        r = new Nod;
        r->info = info;
        read_tree(r->st);
        read_tree(r->dr);
    }
    else
        return 0;
}

void RSD(Nod *r)
{
    if (r != NULL)
    {
        cout << r->info << " ";
        RSD(r->st);
        RSD(r->dr);
    }
}

int main()
{
    Nod *r = NULL;
    read_tree(r);
    system("Pause");
    cout << r->st->st->info << endl;
    cout << r->dr->info;
    RSD(r);
}

Answer 1

The problem is that you pass a copy of a pointer to a read_tree function. That is, when you call read_tree(r) in the main function, r remains NULL regardless of what happens inside the read_tree function. You can fix it by passing a pointer by reference. That is, changing read_tree(Nod* r) to read_tree(Nod*& r) should fix it.