如何在C ++中从原始指针转换为唯一指针

Question

So, I thought that by converting from raw pointer to unique pointer was not hard at all. However, as I am trying to attempt to do one for myself, I run into a lot of problems that I don't even know of. This example below will explain more what I mean. I got a lot of errors from Visual Studio that I don't know how to fix it. Can I anyone tell me what I did wrong ? Thank you

Contact.h

#pragma once
#include<iostream>
#include<string>
#include<memory>

class Contact
{
    friend std::ostream& operator<<(std::ostream& os, const Contact& c);
    friend class ContactList;

public:
    Contact(std::string name = "none");

private:
    std::string name;
    //Contact* next;    
    std::unique_ptr<Contact> next;
};

Contact.cpp

#include"Contact.h"

using namespace std;

Contact::Contact(string n):name(n), next(new Contact())
{
}

ostream& operator<<(ostream& os, const Contact& c)
{
    return os << "Name: " << c.name;
}

ContactList.h

#pragma once
#include"Contact.h"
#include<memory>

using namespace std;

class ContactList
{
public:
    ContactList();
    ~ContactList();
    void addToHead(const std::string&);
    void PrintList();

private:
    //Contact* head;
    unique_ptr<Contact> head;
    int size;
};

ContactList.cpp

#include"ContactList.h"
#include<memory>

using namespace std;

ContactList::ContactList(): head(new Contact()), size(0)
{
}

void ContactList::addToHead(const string& name)
{
    //Contact* newOne = new Contact(name);
    unique_ptr<Contact> newOne(new Contact(name));

    if(head == 0)
    {
        head.swap(newOne);
        //head = move(newOne);
    }
    else
    {
        newOne->next.swap(head);
        head.swap(newOne);
        //newOne->next = move(head);
        //head = move(newOne);
    }
    size++;
}

void ContactList::PrintList()
{
    //Contact* tp = head;
    unique_ptr<Contact> tp(new Contact());
    tp.swap(head);
    //tp = move(head);

    while(tp != 0)
    {
        cout << *tp << endl;
        tp.swap(tp->next);
        //tp = move(tp->next);
    }
}

I updated by using swap function to swap the content between pointers.

Here is all the errors that I get

Error   2   error LNK1120: 1 unresolved externals   E:\Fall 2013\CPSC 131\Practice\Practice\Debug\Practice.exe  1

Error 1 error LNK2019: unresolved external symbol "public: __thiscall ContactList::~ContactList(void)" (??1ContactList@@QAE@XZ) referenced in function "public: void * __thiscall ContactList::`scalar deleting destructor'(unsigned int)" (??_GContactList@@QAEPAXI@Z) E:\\Fall 2013\\CPSC 131\\Practice\\Practice\\Practice\\ContactListApp.obj

Answer 1

unique_ptr has empty constructor and nullptr constructor, it says nothing about 0.

constexpr unique_ptr();
constexpr unique_ptr( nullptr_t );
explicit unique_ptr( pointer p );
unique_ptr( pointer p, /* see below */ d1 );
unique_ptr( pointer p, /* see below */ d2 );
unique_ptr( unique_ptr&& u );
template< class U, class E >
unique_ptr( unique_ptr<U, E>&& u );
template< class U >
unique_ptr( auto_ptr<U>&& u );

also, you're going to want to use void swap(unique_ptr& other) to swap pointers between unique_ptrs without deconstructing them as would happen with the operator= . Try again with all that in mind, you should take a good look at the cppreference.com unique_ptr page to understand how it works.

On a second note with linked lists if I were you I'd use raw pointers.