Postincrementation operator in linked list - c++

I had to write a program that handle this main code:(not allowed to change it)
list<int> iv;
iv["john"] = 23;
int ia = iv["john"]++;
int ib = iv["john"];
cout << ia << " " << ib << endl; // prints 23 24
try{
cout << iv["jack"] << endl; // should throw an exception
}catch(list<int>::Uninitialized&)
{
cout << "Uninitialized map element!" << endl;
};
Here is my code:
#ifndef EXAM_H
#define EXAM_H
#include <iostream>
#include <string>
using namespace std;
template <class TYPE>
class list
{
private:
struct node
{
TYPE value;
string index;
bool isInit;
node *next;
};
node *head;
node *current;
public:
class Cref
{
friend class list;
list& s;
string position;
Cref (list& ss, string pos): s(ss), position(pos) {};
public:
operator TYPE() const
{
return s.read(position);
}
Cref& operator = (TYPE val)
{
s.write(position,val);
return *this;
};
Cref& operator = (const Cref& ref)
{
return operator= ((TYPE)ref);
};
};
class Uninitialized{};
list ()
{
cout << "constructor\n";
head = NULL;
current = NULL;
}
~list ()
{
while (head)
{
node *t = head->next;
delete head;
head = t;
};
}
TYPE read (string ind) const
{
cout << "read\n";
node *t = head;
while(t)
{
if(t->index == ind && t->isInit == true) return t->value;
else t = t->next;
}
throw Uninitialized();
}
void write (string ind, TYPE value_)
{
cout << "write\n";
node *t = new node;
t->next = head;
head = t;
head->value = value_;
head->index = ind;
head->isInit = true;
}
TYPE operator[] (string ind) const
{
cout << "read\n";
node *t = head;
while(t)
{
if(t->index == ind && t->isInit == true) return t->value;
else t = t->next;
}
throw Uninitialized();
}
Cref operator[] (string ind)
{
return Cref(*this, ind);
}
};
#endif
Everything works great, but only when I comment out postincrementation operation in main program
int ia = iv["john"]++;
As you can see I have a struct node where I put all variables and I want to increment value by one in node where the key is "john". Is there any way to implement operator++ for this code ?
I am not allowed to use std::map.

The usual approach to your problem is defining the array subscript operators as
const TYPE& operator[](string ind) const;
TYPE& operator[](string ind);
In this way, you do not have to bother a single bit about the operator++: Since iv["John"] returns a reference to int, iv["John"]++ will call the int post-increment operator which is built-in.

Yes, I have already tried this solution, but compiler do not distinguish between reading and writing and still using non-const version. So I had to build proxy class Cref that helps to distinguish.
I have also already find a solution to operator++ problem.
This operation had to be from Cref level. I created
Cref& operator++ (int val)
{
s.increment(position,val);
return *this;
};
And increment function in main class body as follows:
void increment (string ind, int value_)
{
cout << "increment\n";
node *t = head;
while(t)
{
if(t->index == ind && t->isInit == true) t->value = t->value + 1;
t = t->next;
}
}
That fully solved my problem.

Related

A reference of type "Bucket&" (not const qualified) cannot be initialized with a value of type "SortedList." How can this error be fixed?

The error occurs in my SortedList class in function method sortList. I have tried to rename, remove, move, and manipulate certain things to no avail. I will show you a good amount of code so that you can see where I'm coming from.
void SortedList::sortList(const vector <double>& list) {
BucketSort bucketA;
bucketA.insert(list);
bucketA.createSortedList(*this); // <--- Problem here, on this one line.
// The * is highlighted in red in my IDE.
}
Error: A reference of type "Bucket&" (not const qualified) cannot be initialized with a value of type "SortedList"
For reference, if you need to see to get a context of my error:
SortedList.h:
#ifndef SORTEDLIST_H
#define SORTEDLIST_H
#include "bucketsort.h"
#include <vector>
using namespace std;
class SortedList
{
public:
SortedList();
void sortList(const vector <double>& list);
~SortedList();
private:
};
#endif
Bucketsort.h:
#ifndef BUCKETSORT_H
#define BUCKETSORT_H
#include "bucket.h"
#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;
const int DEFAULTCAPACITY = 10;
class BucketSort
{
public:
// Constructors:
BucketSort();
// Functions:
void print() const;
void insert(const vector <double>& v) const;
void createSortedList(Bucket& a);
//
~BucketSort();
private:
Bucket ** a;
};
#endif
Bucketsort.cpp:
#include "bucketsort.h"
BucketSort::BucketSort() {
a = new Bucket*[DEFAULTCAPACITY]();
}
void BucketSort::print() const {
for (int i = 0; i < DEFAULTCAPACITY; ++i) {
if (a[i] != nullptr) {
a[i]->print();
}
}
}
void BucketSort::insert(const vector <double>& v) const {
int index;
for (int i = 0; i < v.size(); ++i) {
index = v[i] * 10;
if (a[index] == nullptr) {
Bucket* newBucket = new Bucket;
a[index] = newBucket;
}
a[index]->insert(v[i]);
}
}
void BucketSort::createSortedList(Bucket& a){
}
BucketSort::~BucketSort() {
for (int i = 0; i < DEFAULTCAPACITY; ++i) {
if (a[i] != nullptr) {
a[i]->deleteBucket();
}
}
delete a;
a = nullptr;
}
Bucket.h:
#ifndef BUCKET_H
#define BUCKET_H
#include <iostream>
using namespace std;
class Node
{
public:
Node() : item(0.0), link(nullptr) {}
Node(double newItem, Node *newLink) : item(newItem), link(newLink) {}
Node* getLink() const { return link; }
double getItem() const { return item; }
void setItem(double newItem) { item = newItem; }
void setLink(Node *newLink) { link = newLink; }
~Node() {}
private:
double item;
Node *link;
};
class Bucket
{
public:
Bucket();
void insert(double value);
void testPrint() const;
void print() const;
int getNumberOfElements() const;
void deleteBucket();
~Bucket();
private:
Node * ptrToFirst;
Node *ptrToLast;
int numberOfElements;
};
#endif
Bucket.cpp:
#include "bucket.h"
Bucket::Bucket() {
ptrToFirst = nullptr;
ptrToLast = nullptr;
numberOfElements = 0;
}
void Bucket::insert(double value) {
if (numberOfElements != 0) {
Node *newNode = new Node(value, nullptr);
if (value < ptrToFirst->getItem()) {
newNode->setLink(ptrToFirst);
ptrToFirst = newNode;
}
else if (value > ptrToLast->getItem()) {
ptrToLast->setLink(newNode);
ptrToLast = newNode;
}
else if (value != ptrToFirst->getItem()) {
Node *current = ptrToFirst;
while (value > current->getLink()->getItem()) {
current = current->getLink();
}
if (current->getLink()->getItem() != value) {
newNode->setLink(current->getLink());
current->setLink(newNode);
}
}
}
else {
ptrToFirst = new Node(value, ptrToLast);
ptrToLast = ptrToFirst;
}
++numberOfElements;
}
void Bucket::testPrint() const {
cout << "Pointer to first: " << ptrToFirst << endl;
cout << "Pointer to last: " << ptrToLast << endl;
if (ptrToFirst != nullptr && ptrToLast != nullptr) {
cout << "Value of ptrToFirst: " << ptrToFirst->getItem() << endl;
cout << "Value of ptrToLast: " << ptrToLast->getItem() << endl;
}
cout << "Number of elements: " << numberOfElements << endl;
cout << "Contents of bucket: " << endl;
Node *current = ptrToFirst;
while (current != nullptr) {
cout << current->getItem() << " ";
current = current->getLink();
}
cout << endl;
}
void Bucket::print() const {
Node *current = ptrToFirst;
while (current != nullptr) {
cout << current->getItem() << " ";
current = current->getLink();
}
}
int Bucket::getNumberOfElements() const {
return numberOfElements;
}
void Bucket::deleteBucket() {
Node *trailingCurrent;
while (ptrToFirst != nullptr) {
trailingCurrent = ptrToFirst;
ptrToFirst = ptrToFirst->getLink();
delete trailingCurrent;
trailingCurrent = nullptr;
}
ptrToLast = nullptr;
numberOfElements = 0;
}
Bucket::~Bucket() {
deleteBucket();
}
Help?
void SortedList::sortList(const vector <double>& list) {
[...]
bucketA.createSortedList(*this); // <--- Problem here
In the above line, this is of type SortedList *, so *this is of type SortedList &.
... and yet, your createdSortedList method requires an argument of a different type, Bucket &:
void createSortedList(Bucket& a);
Since a SortedList and a Bucket are not the same type, and there is no way (that the compiler knows about) to convert a SortedList object into a Bucket object, the compiler is rightly flagging the call as an error.
To solve the problem, you either need to change createSortedList to take a SortedList & as its argument, instead of a Bucket &, or change your call to pass in a Bucket & instead of a SortedList &.

Trouble implementing a templated singly linked list

I'm trying to implement a templated singly linked list and I'm fairly new to C++
#include <iostream>
#include <string>
#define NEWL "\n"
#define PRINT(s) std::cout << s
#define PRINTL(s) std::cout << s << NEWL
#define PRINTERR(e) std::cerr << e << NEWL
////// Class for a Node
template<class Data> class Node {
Node<Data>* next_ptr;
Data data;
public:
Node(Node<Data>* nxt_ptr) :next_ptr(nxt_ptr) {};
Node(Data d, Node<Data>* nxt_ptr) :data(d), next_ptr(nxt_ptr) {};
Node<Data>* get_next() { return next_ptr; }
Data& get_data() { return data; }
friend std::ostream& operator<<(std::ostream& out, const Node<Data>& node) {
out << node.data;
return out;
};
};
////// Class for a SinglyLinkedList
template<class Data> class SLinkedList {
Node<Data>* head_ptr;
int max_size;
public:
SLinkedList() : head_ptr(nullptr) {};
bool is_empty() {
return head_ptr == nullptr;
};
bool is_full() {
return get_size() == max_size;
};
int get_size() {
if (is_empty()) {
return 0;
}
int count = 0;
for (Node<Data>* it_ptr = head_ptr; it_ptr != nullptr; it_ptr = it_ptr->get_next()) {
count++;
}
return count;
};
void add(Data d) {
if (is_full()) {
throw std::exception("List is full!");
}
Node<Data> new_node(d, head_ptr);
head_ptr = &new_node;
};
void print_content() {
int count = 1;
PRINTL("This list contains:");
for (Node<Data>* it_ptr = head_ptr; it_ptr != nullptr; it_ptr = it_ptr->get_next()) {
PRINTL("\t["<< count << "]" << " at " << it_ptr << " : " << *it_ptr);
count++;
}
}
};
////// Main function
int main()
{
SLinkedList<int> sll;
sll.add(42);
sll.print_content();
}
I can't get this to work. Somehow iterating the list with for-loops does not work. It always results in an Reading Access Violation Exception about a pointer to 0xCCCCCCD0 and I have no idea how to fix this.
Your add function is incorrect
Node<Data> new_node(d, head_ptr);
creates a new function local Node in add. You then set head to the address of that local variable. When the function ends all local variables are destroyed so now head points to an object that no longer exists.
To fix that you need to use the new keyword to create a dynamic object that will live on after the function ends.
Node<Data>* new_node = new Node(d, head_ptr);
head_ptr = new_node;
The down side with this is you need to remember to call delete on all of the nodes you created in the list destructor.
You also have some other bugs in your code. You never set max_size in your constructor so using it at all except to give it a value is undefined behavior as we have no idea what the value of it is going to be. You also never increase the size of the list when you add nodes into the list.

Adding an Instance to a Linked List using a Node

I'm having trouble understanding on how would I call the add function in main if I want to add an instance to list.
#include "object.h"
class list {
private:
struct Node
{
object objectInfo;
Node *next;
};
int size;
Node *head;
public:
list();
list(const list& otherlist);
~list();
void Add(const Node myObject);
my Main
int main() {
object myObject;
myObject.setTitle("Object 1");
myObject.setPrice(78.58);
myObject.setISBN("515161611");
cout << myObject << endl;
list myList;
myList.Add(myObject);
return 0;
}
my Function in cpp
void list::Add(const Node myObject) {
Node* temp;
temp = new Node;
temp->objectInfo = myObject.objectInfo;
temp->next = head;
head = temp;
size++;
}
Im having trouble on this line myList.Add(myObject);
keeps saying void list::Add(const list&)':cannot convert argument 1 from 'object' to 'const list::Node'
also no instance of overloaded function "list::Add" matches the argument list
You are trying to pass an object of type object into a function that takes a parameter of type Node. const Node myObject should be const object myObject.
This might give you some ideas:
#include <iostream>
#include <string>
template <typename Object>
class List {
class Node : public Object {
//static int& count() { static int c=0; return c; }
public:
Node* next;
Node() : next(nullptr) {
//std::cout << ++count() << " Nodes\n";
}
Node(const Object& obj) : next(nullptr), Object(obj) {
//std::cout << ++count() << " Nodes\n";
}
~Node() {
//std::cout << --count() << " Nodes\n";
}
};
Node *head, *tail;
int size;
public:
class iterator {
Node *cur_node;
public:
iterator(Node* node) { cur_node = node; }
Object& operator * () const { return *cur_node; }
bool operator != (const iterator& iter) const { return iter.cur_node != cur_node; }
iterator& operator ++() { if(cur_node) cur_node = cur_node->next; return *this; }
};
class iterator_const {
const Node *cur_node;
public:
iterator_const(const Node* node) { cur_node = node; }
const Object& operator * () const { return *cur_node; }
bool operator != (const iterator_const& iter) const { return iter.cur_node != cur_node; }
iterator_const& operator ++() { if(cur_node) cur_node = cur_node->next; return *this; }
};
iterator begin() { return iterator(head); }
iterator end() { return iterator(nullptr); }
iterator_const begin() const { return iterator_const(head); }
iterator_const end() const { return iterator_const(nullptr); }
template <typename ...Args>
void Add(const Object& obj, Args...more) {
Node *new_node = new Node(obj);
++size;
if(!tail) { tail = head = new_node; }
else { tail->next = new_node; tail = new_node; }
Add(more...);
}
void Add() {}
int Size() const { return size; }
List() : head(nullptr), tail(nullptr), size(0) {}
List(const List& src) : head(nullptr), tail(nullptr), size(0) {
for(auto&& entry : src) {
Add(entry);
}
}
~List() {
Node* p = head;
while(p) {
Node* next = p->next;
delete p;
p = next;
}
}
};
struct MyObjectType {
std::string name;
int age;
MyObjectType(std::string name, int age) : name(name), age(age) {}
friend std::ostream& operator << (std::ostream& os, const MyObjectType& obj) {
return os << "{\"" << obj.name << "\":" << obj.age << "}";
}
};
template <typename T>
void PrintList(const List<T>& list) {
std::cout << "Size: " << list.Size() << "\n";
for(const auto &elem : list) {
std::cout << " " << elem << "\n";
}
}
int main() {
using MyList = List<MyObjectType>;
MyList list_one;
list_one.Add(
MyObjectType("Harry",32),
MyObjectType("Lisa", 66),
MyObjectType("Buddy", 2),
MyObjectType("Skippy", 21)
);
MyList list_two(list_one);
list_two.Add(
MyObjectType("Horse", 10),
MyObjectType("Mule", 11)
);
std::cout << "list_one:\n";
PrintList(list_one);
std::cout << '\n';
std::cout << "list_two:\n";
PrintList(list_two);
}

How to access array elements of pointers

How can I access elements from my Node pointer array? The cout at the bottom returns an address "0xb7738ff4". Even if I make a constructor and set each element to NULL, I cannot modify any of them later on.
#include <iostream>
using namespace std;
class Node
{
public:
char character;
};
class Tree
{
public:
Node* nodes[26];
};
int main() {
Tree t;
//t.nodes[0]->character = 'a';
cout << "\"" << (t.nodes[0]) << "\"";
}
http://ideone.com/XvLme9
t.nodes[0] is returning a Node* pointer. You are passing that pointer as-is to cout, that is why it is printing a memory address (and a random one at that, because you are not initializing the array). If you want to print the character of a node, you have to dereference the Node* pointer, exactly like your commented out code is doing (which is the correct way to do it):
t.nodes[0]->character
You just have to make sure that nodes[0] returns a valid pointer to a real Node object to begin with:
Tree t;
t.nodes[0] = new Node; // <-- here
t.nodes[0]->character = 'a';
std::cout << "\"" << t.nodes[0]->character << "\"" << std::endl;
Don't forget to delete the node when you are done using it. Tree should have a destructor that frees the nodes it owns.
Try something more like this:
#include <iostream>
#include <stdexcept>
class Node
{
public:
char character;
Node(char c = 0);
};
class Tree
{
private:
Node* nodes[26];
int count;
public:
Tree();
~Tree();
Node* add(char c);
Node* get(int idx);
};
Node::Node(char c)
: character(c)
{
}
Tree::Tree()
: count(0)
{
for (int i = 0; i < 26; ++i)
nodes[i] = NULL;
}
Tree::~Tree()
{
for (int i = 0; i < count; ++i)
delete nodes[i];
}
Node* Tree::add(char c)
{
if (count == 26)
throw std::runtime_error("nodes array is at its max capacity");
Node *node = new Node(c);
nodes[count++] = node;
return node;
}
Node* Tree::get(int idx)
{
if ((idx < 0) || (idx >= count))
throw std::out_of_range("invalid index");
return nodes[idx];
}
int main()
{
Tree t;
t.add('a');
std::cout << "\"" << t.get(0)->character << "\"" << std::endl;
}
With that said, you should use std::list or std::forward_list instead of writing your own tree class:
#include <list>
int main()
{
std::list<char> l;
l.push_back('a');
std::cout << "\"" << l.front() << "\"" << std::endl;
}
Or:
#include <list>
class Node
{
public:
char character;
// other things here...
Node(char c = 0);
Node(const Node &src);
Node& operator=(const Node &rhs);
};
Node::Node(char c)
: character(c)
{
}
Node::Node(const Node &src)
: character(src.character)
{
}
Node& Node::operator=(const Node &rhs)
{
character = src.character;
return *this;
}
int main()
{
std::list<Node> l;
l.push_back('a');
std::cout << "\"" << l.front().character << "\"" << std::endl;
}

Linked list problem with constructor and destructor

Hi
I have some issue regarding constructor and destructor. I have list class, which has two inner classes, one private class for the list nodes, and one public iterator class.
Now for the issue, I have written a non-member print function which uses the inner iterator class. When i use this non-member function it will end calling the destructor for the iterator. It doesn't end here though because for some reason it will also call for the list class's destructor. Which causes some problem when I want to print the list content again.
I don't understand why it call the list class destructor as well and wonder if someone kindly can tell me that, and how I should fix it.
I have attached all the code related to the problem
Main
#include <iostream>
#include "sorted_list.h"
#include "iterator.h"
using namespace std;
void list_print(ostream& os, sorted_list list)
{
sorted_list::iteratorn it(&list);
while( ! it.iterator_end())
{
os << "key = " << setw(3) << it.iterator_get_key() << ", "
<< "value = " << setw(5) << it.iterator_get_value() << endl;
it.iterator_next();
}
os << endl;
}
int main()
{
sorted_list a;
a.insert(4,4);
a.insert(5,5);
list_print(cout,a);
list_print(cout,a);
}
sorted_list.cc
#include "sorted_list.h"
sorted_list::sorted_list()
{
cout << "construct sorted_list" << endl;
this->first = 0;
}
sorted_list::~sorted_list()
{
cout << "destruct sorted_list" << endl;
destroy(this->first);
}
void sorted_list::destroy(list_link* item)
{
cout << "destroy list_link" << endl;
if(item)
{
destroy(item->next);
delete item;
}
}
void sorted_list::insert(int key, double value)
{
list_link *curr;
list_link *prev = 0;
curr = first;
while(curr)
{
if(value < curr->value)
break;
prev = curr;
curr = curr->next;
}
if(this->first == 0 || prev == 0) //if empty or add first
{
//first = create(key, value, this->first);
first = new list_link(key, value, this->first);
}
else if(curr == 0)
{
//prev->next = create(key, value, 0);
prev->next = new list_link(key, value, 0);
}
else
{
//prev->next = create(key, value, curr);
prev->next = new list_link(key, value, curr);
}
}
void sorted_list::remove(my_key_type key)
{
list_link *curr = first;;
list_link *prev = 0;
while(curr)
{
if(curr->key == key)
{
list_link *remove;
if(prev == 0)
{
first = curr->next;
delete curr;
curr = first;
}
else
{
remove = curr;
curr = curr->next;
prev->next = curr;
delete remove;
}
continue;
}
prev = curr;
curr = curr->next;
}
}
sorted_list::list_link* sorted_list::clone(list_link* item)
{
list_link* copyItem= new list_link(item->key,item->value,0);
if(item->next!= 0)
copyItem->next=clone(item->next);
return copyItem;
// ADD YOUR CODE HERE ( 4 well formatted lines in reference solution )
}
void sorted_list::copy(sorted_list* my_this_destination)
{
if (my_this_destination->first == 0) // copy if empty
{
cout << "Copy" << endl;
//list_destroy(my_this_destination);
my_this_destination->first = clone(first);
}
}
double sorted_list::find(int key)
{
list_link *travel = this->first;
while(travel)
{
cout << travel->key << "==" << key << endl;
if(travel->key == key)
return travel->key;
travel = travel->next;
}
return -1;
}
int sorted_list::size()
{
list_link *travel = this->first;
int i = 0;
while( travel )
{
travel = travel->next;
i++;
}
return i;
}
sorted_list.h
#ifndef _SORTED_LIST_H_
#define _SORTED_LIST_H_
#include <iostream>
#include <iomanip>
using namespace std;
typedef int my_key_type;
typedef double my_value_type;
class sorted_list
{
public:
sorted_list();
~sorted_list();
void insert(int key, double value);
void remove(my_key_type key);
void copy(sorted_list* my_this_destination);
void destroy();
void init(struct my_list* my_this);
void print();
void print2();
double find(int key);
int size();
private:
class list_link // An inner class inside sorted_list
{
public:
list_link (my_key_type key, my_value_type value, list_link* next = 0);
~list_link();
my_key_type key;
my_value_type value;
list_link *next;
};
list_link* first;
list_link* clone(list_link* item);
void destroy(list_link* item);
// More declarations
public:
class iteratorn
{
public:
iteratorn();
~iteratorn();
iteratorn(sorted_list *item);
list_link* list_begin();
bool iterator_end();
void iterator_next();
int iterator_get_key();
double iterator_get_value();
private:
sorted_list::list_link* current;
};
};
#endif
iteratorn.cc
#include "iterator.h"
#include "sorted_list.h"
sorted_list::iteratorn::iteratorn()
{
}
sorted_list::iteratorn::iteratorn(sorted_list *list)
{
cout << "construct iteratorn" << endl;
this->current = list->first;
}
sorted_list::iteratorn::~iteratorn()
{
cout << "destruct iteratorn" << endl;
}
sorted_list::list_link* sorted_list::iteratorn::list_begin()
{
return current;
}
void sorted_list::iteratorn::iterator_next()
{
current = current->next;
}
int sorted_list::iteratorn::iterator_get_key()
{
return current->key;
}
double sorted_list::iteratorn::iterator_get_value()
{
return current->value;
}
list_link.cc
#include "sorted_list.h"
sorted_list::list_link::list_link(my_key_type key, my_value_type value, list_link* next)
{
this->key = key;
this->value = value;
this->next = next;
}
sorted_list::list_link::~list_link()
{
cout << "list_link destructor" << endl;
}
Your function void list_print(ostream& os, sorted_list list) takes a sorted_list parameter by copy. A quick and dirty fix (that you should do anyways for performance reasons) is the following:
void list_print(ostream& os, const sorted_list& list)
Now, your iteratornclass takes a mutable list, so this won't work as you expect. You will have quite a few methods to change to make this work.
In any case, your real problem is the lack of a proper copy-constructor. Right now, when you "copy" a list, both end up sharing the same elements, but your destructor is written as if each list owns it's own nodes. Define a proper copy operation and it will solve your problem.
More elaborate help on how to solve the problem: (untested)
Change signature:
void list_print(ostream& os, const sorted_list& list);
Declare + define copy constructor:
sorted_list::sorted_list (const sorted_list& other);
Change iteratorn interface to support a const sorted_list:
class sorted_list::iteratorn
{
public:
iteratorn();
~iteratorn();
iteratorn(const sorted_list& list);
const list_link* list_begin() const;
bool iterator_end() const;
void iterator_next();
int iterator_get_key() const;
double iterator_get_value() const;
private:
// You *should* make this `const` but it is not required.
sorted_list::list_link* current;
};
As you can see, the changes are rather minimal, but need to be applied in various places.
const + non-const iterators:
I applied changes here based on the fact that your iteratorn was currently only defining read-only operations on your sorted_list. If you want to support write access to allow changing the value stored in list nodes (never allow changing the key or you won't have a sorted list anymore), you should define two iterator classes. See the STL iterator interface for more details.
You're copying the list by value, so the local copy in list_print() destructs at end of scope. Pass it by const-reference instead.
This in turn means you will have to change your sorted_list to support working with const lists. In particular you need to have a function that returns a const iterator pointing to the beginning of the list:
sorted_list::const_iteratorn begin() const
{
// returns a const_iteratorn pointing at the beginning of this list
}
Notice you need a new kind of iterator: a const_iteratorn, which promises it won't change the list.
Then, inside print_list() initialize a const_iteratorn with the start iterator that sorted_list returns, by copy:
sorted_list::const_iteratorn s(list.begin());
Finally create a second iterator instance that initializes with an end iterator coming from a member function of sorted_list, similar to the begin() function. This will maintain the const-correctness in print_list().
sorted_list::const_iteratorn e(list.end());
while( s != e ) { // two iterators should be able to compare
// ...
s.iterator_next(); // consider ++s
}
Also, as André mentioned, the fact you don't have a proper copy-constructor and assignment operator is a severe issue. Make sure that copying a sorted_list means copying all its elements, so that the new object owns its own list of elements. Do recall the Rule of Three.