Two objects (one is in a list<>) share same memory address i.e. if one is changed, it changes the other one in the list

Question

I have put a lot of effort and research into this and I'm stuck. I've tried a copy constructor, a copy function and a Memberwise Clone function, but none of these seemed to work. The elements in Matrix[0] shouldn't change, but a change in g1 does so.

If anyone knows how to fix this, please reply.

I'm adding additional text so I can post my question.

class Game
    {
        public Game()
        {

        Card_ID = 1;

        EmptyMainMonsterZones = 5;
        EmptyExtraMonsterZones = 1;
        EmptySpellTrapZones = 5;

        LP = 8000;

        NormalSummons = 1;

        DrawnCards = 0;

        LastEvent = "";

        CardPool = new List<Card>();

        ScenarioSteps = new List<string>();
    }

    public Game(Game other)
    {
        Card_ID = other.Card_ID;

        EmptyMainMonsterZones = other.EmptyMainMonsterZones;
        EmptyExtraMonsterZones = other.EmptyExtraMonsterZones;
        EmptySpellTrapZones = other.EmptySpellTrapZones;

        LP = other.LP;

        NormalSummons = other.NormalSummons;

        DrawnCards = other.DrawnCards;

        LastEvent = other.LastEvent;

        //CardPool = new List<Card>(other.CardPool);

        CardPool = new List<Card>();

        foreach (Card c in other.CardPool)
        {
            CardPool.Add(c);
        }

        //ScenarioSteps = new List<string>(other.ScenarioSteps);

        ScenarioSteps = new List<string>();

        foreach (string s in other.ScenarioSteps)
        {
            ScenarioSteps.Add(s);
        }
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }

    int Card_ID;

    public int EmptyMainMonsterZones;
    public int EmptyExtraMonsterZones;
    public int EmptySpellTrapZones;

    public int LP;

    public int NormalSummons;

    public int DrawnCards;

    public string LastEvent;

    public List<Card> CardPool = new List<Card>();

    public List<string> ScenarioSteps = new List<string>();

    public void Init(string name,string location,string position = "-")
    {
        Card c = new Card(name);

        if(location == "Main Monster Zone")
        {
            c.SetLocation(location);
            EmptyMainMonsterZones--;
        }
        else if (location == "Extra Monster Zone")
        {
            c.SetLocation(location);
            EmptyExtraMonsterZones--;
        }
        else
        {
            c.SetLocation(location);
            c.SetPosition(position);
            c.SetCard_ID(Card_ID);
            Card_ID++;
            CardPool.Add(c);
        }
    }

    public void PrintScenarioSteps()
    {
        for(int i=0;i<ScenarioSteps.Count;i++)
        {
            Console.WriteLine(ScenarioSteps[i]);
        }
    }

    public void Print()
    {
        for(int i=0;i<CardPool.Count;i++)
        {
            if(!CardPool[i].IsLocation("No Location"))
            {
                Console.WriteLine("{0} ({1}) is in the {2}", CardPool[i].getName(), CardPool[i].getLevel(), CardPool[i].getLocation());
            }
        }
    }

    // Checks
    bool IsCanBeNormalSummoned(Card c)
    {
        if (c.IsLevelBelow(4) && c.IsLocation("Hand") && EmptyMainMonsterZones > 0 && NormalSummons > 0) return true;
        if (c.IsException("Normal Summon without Tribute") && c.IsLocation("Hand") && EmptyMainMonsterZones > 0 && NormalSummons > 0) return true;
        return false;
    }

    // Operations

    public bool NormalSummon(ref Card c)
    {
        if(IsCanBeNormalSummoned(c))
        {
            c.SetPreviousLocation(c.getLocation());
            c.NormalSummoned = true;
            c.SetLocation("Main Monster Zone");

            EmptyMainMonsterZones--;
            NormalSummons--;
            LastEvent = "Normal Summon";

            if(!c.Negated)
            {
                if(c.IsName("Fusilier Dragon, the Dual-Mode Beast"))
                {
                    c.SetAttack(c.getAttack()/2);
                    c.SetDefense(c.getDefense()/2);
                }
            }

            return true;
        }
        return false;
    }
}

class Program
{
    static List<Game> Matrix = new List<Game>();

    static void Main(string[] args)
    {
        Game Duel = new Game();

        Duel.Init("Level Eater", "Hand");
        Duel.Init("Junk Forward", "Hand");
        Duel.Init("Fusilier Dragon, the Dual-Mode Beast","Hand");

        Matrix.Add(Duel);

        Game g1 = new Game(Matrix[0]);

        Console.WriteLine("g1:");
        g1.Print();
        Console.WriteLine();

        Console.WriteLine("Matrix[0]:");
        Matrix[0].Print();
        Console.WriteLine();

        Card c1 = g1.CardPool[0];

        if (g1.NormalSummon(ref c1))
        {
            string s = "Normal Summon " + g1.CardPool[0].getName() + ".";
            g1.ScenarioSteps.Add(s);

            Console.WriteLine("After Normal Summon:");
            Console.WriteLine("g1:");
            g1.Print(); // Pointing to the same address!!!
            Console.WriteLine();

            Console.WriteLine("Matrix[0]:");
            Matrix[0].Print(); // This changes, too!!!
            Console.WriteLine();

            Matrix.Add(g1);
        }

        g1 = new Game(Matrix[0]);

        if (Matrix[0].CardPool[0].IsLocation("Main Monster Zone")) Console.WriteLine("Yes, but I shouldn't be changed!");
        if (g1.CardPool[0].IsLocation("Main Monster Zone")) Console.WriteLine("Yes!");

        Card c2 = g1.CardPool[1];

        if (g1.NormalSummon(ref c2))
        {
            string s = "Normal Summon " + g1.CardPool[1].getName() + ".";
            g1.ScenarioSteps.Add(s);

            g1.Print();
            Console.WriteLine();

            g1.CardPool[0].Print();
            Console.WriteLine();

            Matrix.Add(g1);
        }

        g1 = new Game(Matrix[0]);

        Card c3 = g1.CardPool[2];

        if (g1.NormalSummon(ref c3))
        {
            string s = "Normal Summon " + g1.CardPool[2].getName() + ".";
            g1.ScenarioSteps.Add(s);

            g1.Print();
            Console.WriteLine();

            Matrix.Add(g1);
        }

        Console.WriteLine("Matrix Count: " + Matrix.Count);

        Console.ReadKey();
     }
}

Your "copy constructor" is wrong ... if you are store some **not value type** in Game class then you should do copy of it ... this code is mostly irrelevant ... but I see `ScenarioSteps` which seems to be some list ... you cannot just do `this.ScenarioSteps = g.ScenarioSteps` in constructor .. you nedd to create new instance of list and every of its element — Selvin, Jan 24 '20 at 15:22
I don´t see any copy-constructor. You´re providing `Matrix[0]` and thus `Duel` to `g1`. Not sure how the constructor looks like, but chances are high you´re only doing a shallow instead of a deep copy copy. See here for example: https://stackoverflow.com/questions/78536/deep-cloning-objects — MakePeaceGreatAgain, Jan 24 '20 at 15:23

Jawad · Answer 1 · 2020-01-25T17:41:16.503

0

I would recommend using a method to copy the object instead of using a reference to another object that will also get updated. You can add this method to your Game class that can be invoked for any Game object.

Serializing the object converts it to a string and then deserialize changes it back to a new object (without any references to original object).

    public Game Clone(Game other)
    {
        return JsonConvert.DeserializeObject<Game>(JsonConvert.SerializeObject(other));
    }

What this does is creates a new copy of the original object and changing anything within this new object will not affect the orginal list or game object you had.

You can use the above method like this,

Game g1 = new Game().Clone(Matrix[0]);

You can also use deserialize in your main program,

Game g1 = JsonConvert.DeserializeObject<Game>(JsonConvert.SerializeObject(Matrix[0]);

EDIT: Use this to test your code

I took out Card because the implementation of that was not available. Other than that, your code works fine. You dont need to use ref because C# natively uses references of classes when passed as arguments.

edited Jan 25 '20 at 17:41

answered Jan 24 '20 at 15:47

Jawad

11,028
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It's still not working. g1 copies nothing from Matrix[0]. – Давид Желев Jan 25 '20 at 16:20
Did you copy this method inside your Game class ? – Jawad Jan 25 '20 at 16:21
Yes, i did. What can I do next? Should I use the ref keyword? – Давид Желев Jan 25 '20 at 16:23
When you call new Game(), its creating a new instance of Game object that has a built in method to take a Game object and create a new copy of it. What is the error you are getting – Jawad Jan 25 '20 at 16:32
Also.. check to make sure your Matrix[0] has an initialized value. If Matrix[0] is null, it wont work either. – Jawad Jan 25 '20 at 16:34
I'm just translating my C++ code into C#. I didn't have any issues with this in C++, since i can directly write g1=Matrix[0] and the compiler will "understand" what I want to do, but with C#, this is hell of a problem. – Давид Желев Jan 25 '20 at 16:34
You can also write it like this: `Game g1 = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(Matrix[0]);`. This will also work – Jawad Jan 25 '20 at 16:35
g1: Matrix[0]: Level Eater (1) is in the Hand Junk Forward (3) is in the Hand Fusilier Dragon, the Dual-Mode Beast (7) is in the Hand Matrix Count: 1 This is the output. – Давид Желев Jan 25 '20 at 16:41
@ДавидЖелев See my update above. – Jawad Jan 25 '20 at 17:41

score 0 · Answer 2 · answered Jan 25 '20 at 18:04

My solution consists to implement ICloneable interface and using a Clone method as show below :

public object Clone()
{
    return this.MemberwiseClone();
}

the second step is to pass to your Game Constructor a Copy of you object as you can see

Game g1 = new Game((Game)Matrix[0].Clone());

Complete Code Below :

    static void Main(string[] args)
    {

            Game Duel = new Game();

            Duel.Init("Level Eater", "Hand");
            Duel.Init("Junk Forward", "Hand");
            Duel.Init("Fusilier Dragon, the Dual-Mode Beast", "Hand");

            Matrix.Add(Duel);

            Game g1 = new Game((Game)Matrix[0].Clone());

            Console.WriteLine("g1:");
            g1.Print();
            Console.WriteLine();

            Console.WriteLine("Matrix[0]:");
            Matrix[0].Print();
            Console.WriteLine();

            Card c1 = g1.CardPool[0];

            if (g1.NormalSummon(ref c1))
            {
                string s = "Normal Summon " + g1.CardPool[0].getName() + ".";
                g1.ScenarioSteps.Add("dsqdqdqdq");

                Console.WriteLine("After Normal Summon:");
                Console.WriteLine("g1:");
                g1.Print(); // Pointing to the same address!!!
                Console.WriteLine();

                Console.WriteLine("Matrix[0]:");
                Matrix[0].Print(); // This changes, too!!!
                Console.WriteLine();

                Matrix.Add(g1);
            }

            g1 = new Game((Game)Matrix[0].Clone());

            if (Matrix[0].CardPool[0].IsLocation("Main Monster Zone")) Console.WriteLine("Yes, but I shouldn't be changed!");
            if (g1.CardPool[0].IsLocation("Main Monster Zone")) Console.WriteLine("Yes!");

            Card c2 = g1.CardPool[1];

            if (g1.NormalSummon(ref c2))
            {
                string s = "Normal Summon " + g1.CardPool[1].getName() + ".";
                g1.ScenarioSteps.Add(s);

                g1.Print();
                Console.WriteLine();

                g1.CardPool[0].Print();
                Console.WriteLine();

                Matrix.Add(g1);
            }

            g1 = new Game((Game)Matrix[0].Clone());

            Card c3 = g1.CardPool[2];

            if (g1.NormalSummon(ref c3))
            {
                string s = "Normal Summon " + g1.CardPool[2].getName() + ".";
                g1.ScenarioSteps.Add(s);

                g1.Print();
                Console.WriteLine();

                Matrix.Add(g1);
            }

            Console.WriteLine("Matrix Count: " + Matrix.Count);

            Console.ReadKey();

    }

public class Game : ICloneable
{
    public Game()
    {

        Card_ID = 1;

        EmptyMainMonsterZones = 5;
        EmptyExtraMonsterZones = 1;
        EmptySpellTrapZones = 5;

        LP = 8000;

        NormalSummons = 1;

        DrawnCards = 0;

        LastEvent = "";

        CardPool = new List<Card>();

        ScenarioSteps = new List<string>();
    }

    public Game(Game other)
    {
        Card_ID = other.Card_ID;

        EmptyMainMonsterZones = other.EmptyMainMonsterZones;
        EmptyExtraMonsterZones = other.EmptyExtraMonsterZones;
        EmptySpellTrapZones = other.EmptySpellTrapZones;

        LP = other.LP;

        NormalSummons = other.NormalSummons;

        DrawnCards = other.DrawnCards;

        LastEvent = other.LastEvent;

        //CardPool = new List<Card>(other.CardPool);

        CardPool = new List<Card>();

        foreach (Card c in other.CardPool)
        {
            CardPool.Add(c);
        }

        //ScenarioSteps = new List<string>(other.ScenarioSteps);

        ScenarioSteps = new List<string>();

        foreach (string s in other.ScenarioSteps)
        {
            ScenarioSteps.Add(s);
        }
    }


    int Card_ID;

    public int EmptyMainMonsterZones;
    public int EmptyExtraMonsterZones;
    public int EmptySpellTrapZones;

    public int LP;

    public int NormalSummons;

    public int DrawnCards;

    public string LastEvent;

    public List<Card> CardPool = new List<Card>();

    public List<string> ScenarioSteps = new List<string>();

    public void Init(string name, string location, string position = "-")
    {
        Card c = new Card(name);

        if (location == "Main Monster Zone")
        {
            c.SetLocation(location);
            EmptyMainMonsterZones--;
        }
        else if (location == "Extra Monster Zone")
        {
            c.SetLocation(location);
            EmptyExtraMonsterZones--;
        }
        else
        {
            c.SetLocation(location);
            c.SetPosition(position);
            c.SetCard_ID(Card_ID);
            Card_ID++;
            CardPool.Add(c);
        }
    }

    public void PrintScenarioSteps()
    {
        for (int i = 0; i < ScenarioSteps.Count; i++)
        {
            Console.WriteLine(ScenarioSteps[i]);
        }
    }

    public void Print()
    {
        for (int i = 0; i < CardPool.Count; i++)
        {
            if (!CardPool[i].IsLocation("No Location"))
            {
                Console.WriteLine("{0} ({1}) is in the {2}", CardPool[i].getName(), CardPool[i].getLevel(), CardPool[i].getLocation());
            }
        }
    }

    // Checks
    bool IsCanBeNormalSummoned(Card c)
    {
        if (c.IsLevelBelow(4) && c.IsLocation("Hand") && EmptyMainMonsterZones > 0 && NormalSummons > 0) return true;
        if (c.IsException("Normal Summon without Tribute") && c.IsLocation("Hand") && EmptyMainMonsterZones > 0 && NormalSummons > 0) return true;
        return false;
    }

    // Operations

    public bool NormalSummon(ref Card c)
    {
        if (IsCanBeNormalSummoned(c))
        {
            c.SetPreviousLocation(c.getLocation());
            c.NormalSummoned = true;
            c.SetLocation("Main Monster Zone");

            EmptyMainMonsterZones--;
            NormalSummons--;
            LastEvent = "Normal Summon";

            if (!c.Negated)
            {
                if (c.IsName("Fusilier Dragon, the Dual-Mode Beast"))
                {
                    c.SetAttack(c.getAttack() / 2);
                    c.SetDefense(c.getDefense() / 2);
                }
            }

            return true;
        }
        return false;
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }
}

Two objects (one is in a list<>) share same memory address i.e. if one is changed, it changes the other one in the list

2 Answers2