Overloading << operator in a doubly linked list in C++

Question

I am trying to overload the << operator to be an "insert_first operator" for a double linked list. This should be a simple procedure, and I have overloaded operators before, but I am stuck on this one. I am trying to overload it as:

DLList & DLList::operator << (const int value ) 
{
    insert_first(value);
}

My .h file seems fine, and is similar to other ones online:

#ifndef DLLIST_H
#define DLLISH_H

#include <stdio.h>
#include <iostream>

class ListNode {
public:
    int value; 

    ListNode * next;
    ListNode * prev;

    static int node_count;

    ListNode() {
        node_count++;
    }

    ~ListNode() {
        node_count--;
    }

    static void print_node_count() {
        std::cout << "Node Count: " << node_count << std::endl;
    }
};

class DLList {
private:
    ListNode * head;
public:
    DLList();
    ~DLList();

    void print_list();
    void print_list( std::string list_name );
    void insert_first( int value );

    bool remove( int value );
    void concat_list( DLList * list_to_add );

    DLList & operator << (const int value );
};

and my insert_first function also seems to be working fine:

void DLList::insert_first( int value ) 
{
    ListNode * n = new ListNode();

    n->value = value;
    n->next = head->next;
    n->prev = head;

    head->next = n;
    n->next->prev = n;    
}

The error I'm receiving is a segfault. Any ideas or comments would be much appreciated.

You are not returning anything from operator << when you told the compiler it would return a DLList&. — NathanOliver
– NathanOliver, Commented Dec 17, 2015 at 20:35
You don't return *this meaning operator<< has undefined behavior (no return type in a non-void function) — Chad
– Chad, Commented Dec 17, 2015 at 20:36
that's just the way it's written. head doesn't store a value, it's just there for convenience. — fdzsfhaS
– fdzsfhaS, Commented Dec 19, 2015 at 1:45

fdzsfhaS · Accepted Answer · 2015-12-19 01:46:46Z

1

ok, so as the comments suggested, I needed to return something from the operator like

DLList & DLList::operator << (const int value ) 
{
insert_first(value);
return *this; 
}

edited Dec 19, 2015 at 1:46

answered Dec 17, 2015 at 20:42

fdzsfhaS

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