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CoordA = CoordB; Not work?

CoordA = CoordB; Not work?, Why does my Class data not copy across right?

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Codersys	7 Oct, 2008 - 01:08 PM Post #1
New D.I.C Head Joined: 12 May, 2008 Posts: 12	I have a Bignumber class like this... CODE class BigNumber { public const int MaxUnits = 4; public const float MaxFloat = 1.0f; public const int MaxInt = 1000000; public int sign; public float f; public int[] n = new int[MaxUnits]; .......... ......... etc etc } If I create a BigNumber class say CoordA and CoordB, then do this... CoordB = CoordA; The data from CoordA does not copy to CoordB correctly!!! If I use say Vector3 class for CoordA and CoordB then its fine, just not when I use my own data class!!! Hope this makes sense and that someone will tell me what I`ve done wrong! Is it this bit of code some how?... CODE public int[] n = new int[MaxUnits];
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baavgai

7 Oct, 2008 - 03:06 PM

Post #2

Dreaming Coder

Joined: 16 Oct, 2007
Posts: 1,945

Linux

Thanked 94 times

Dream Kudos: 475

Expert In: C, C++, Java, C#, ASP.NET, PHP, Perl, Python, Oracle, SQL Server, MySql, HTML, JavaScript, Lua

My Contributions

Let's make a Widget:

csharp


class Widget {
	private string name;
	private double grams;
	public Widget(string name, double grams) {
		this.name = name;
		this.grams = grams;
	}
	public string Name { get { return this.name; } }
	public double Grams { 
		get { return this.grams; }
		set { this.grams = value; }
	}
}

And test it:

csharp


Widget a = new Widget("Thingy", 12);
Widget b = a;  // nothing is copied, a and now b references the same object
a.Grams = a.Grams * 2;
Writeline(b.Grams); // prints 24, they are the same thing

If wou want to copy an object, make a method that allows the object to copy itself. The two most common methods are to implement ICloneable or use a copy constructor. We'll use the later.

csharp


class Widget {
	//..
	public Widget(Widget obj) {
		this.name = obj.name;
		this.grams = obj.grams;
	}
	//..
}

And test it:

csharp


Widget a = new Widget("Thingy", 12);
Widget b = new Widget(a);  // new copy
a.Grams = a.Grams * 2;
Writeline(b.Grams); // prints 12, a and b are separate instances

Hope this helps.

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Codersys	7 Oct, 2008 - 03:36 PM Post #3
New D.I.C Head Joined: 12 May, 2008 Posts: 12	Widget b = a; // nothing is copied, a and now b references the same object Ah ha I see now why I was struggling... To solve the problem I had done as you suggest and created a Copy Function like this... CODE public void CopyFrom(BigNumber from) { sign = from.sign; f = from.f; n[0] = from.n[0]; n[1] = from.n[1]; n[2] = from.n[2]; n[3] = from.n[3]; } And was using CoordA.CopyFrom(CoordB) to set A same as B values. I just didn`t realise why A=B was not working! Many thanks indeed for that. I`m sometimes amazed that I have got as far as I have in my space game considering I don`t seem to know much details about c# :-) See my game blog here if you like... www.SpaceUnlimited.blogspot.com
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baavgai	7 Oct, 2008 - 04:31 PM Post #4
Dreaming Coder Joined: 16 Oct, 2007 Posts: 1,945 Thanked 94 times Dream Kudos: 475 Expert In: C, C++, Java, C#, ASP.NET, PHP, Perl, Python, Oracle, SQL Server, MySql, HTML, JavaScript, Lua My Contributions	QUOTE(Codersys @ 7 Oct, 2008 - 07:36 PM) I just didn`t realise why A=B was not working! Here's the trick, if A and B were of type int, it would work. Primitives assign normally, objects essentially assign references. In Java you're not allowed to mention the p-word ( pointers ). It's in the fine print somewhere. But there is a pass by reference thing going on.
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