C# constructor using this

Question

Can somebody explain what means : this(123) in a constructor ?

public class MyObject
{      
    public MyObject(): this(123)
    {
    }
    ............
}

do you perhaps have a `MyObject(int variable){ }` constructor? — default, Oct 22 '13 at 19:23
You can read about constructors [here](http://msdn.microsoft.com/en-us/library/ms173115%28v=vs.90%29.aspx) — default, Oct 22 '13 at 19:24
Why don't you step through the code with a debugger to see what it does? — Servy, Oct 22 '13 at 19:24
Did you [search](http://stackoverflow.com/search?q=%5Bc%23%5D+constructor+this)? We already have some answers that might have worked for you. — crashmstr, Oct 22 '13 at 19:24
I will guess that when I instantiate a new object MyObject, the int parameter is somehow optional but by default set to 123 (like you will make an optional parameter in a method: public void Method(int val =5)) ... — user2818430, Oct 22 '13 at 19:24
this means call of overloaded class constructor which take in one integer parameter. — Shad, Oct 22 '13 at 19:24
Yep I have another constructor, so basically when I call new MyObject() then it will call my second constructor MyObject(int val) with the value 123 ... I got it! — user2818430, Oct 22 '13 at 19:27
See [Using Constructors](http://msdn.microsoft.com/en-us/library/ms173115.aspx), near the bottom, where it says: *A constructor can invoke another constructor in the same object by using the `this` keyword. ...* — Jeppe Stig Nielsen, Oct 22 '13 at 19:28
Let me SymbolHound that for you http://symbolhound.com/?q=c%23+%3A+this%28 (but seriously, that site is extremely useful for searching for symbols and other words that are hard to google) — Tim S., Oct 22 '13 at 19:29

score 3 · Accepted Answer · answered Oct 22 '13 at 19:23

Because your class has another constructor which takes and int as parameter.

public class MyObject
{
    public MyObject()
        : this(123)
    {
    }

    public MyObject(int x) //something like this
    {
    }
}

See: Using Constructors (C# Programming Guide)

A constructor can invoke another constructor in the same object by using the this keyword.

score 2 · Answer 2 · answered Oct 22 '13 at 19:24

2

This means, that you are calling another constructor with the fixed Value "123":

public class MyObject
{      
    public MyObject(): this(123)
    {

    }

    public MyObject(int number)
    {

    }
}

Means: Whenever you call new MyObject(), without any parameter, it equals the call to new MyObject(123);

answered Oct 22 '13 at 19:24

dognose

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*"it equals the call to new MyObject(123);"* Not really.. there can be stuff in the default constructor that is not executed in the other constructors – default Oct 22 '13 at 19:27
In this example, there is nothing in the constructors, so it's equal :P – dognose Dec 13 '22 at 22:46

score 1 · Answer 3 · answered Oct 22 '13 at 19:25

1

this is used to call one constructor from another within the same class. Refer to this article for better understanding.

http://www.codeproject.com/Articles/7011/An-Intro-to-Constructors-in-C

answered Oct 22 '13 at 19:25

Irfan TahirKheli

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score 1 · Answer 4 · answered Oct 22 '13 at 19:25

You have another constructor that accepts an int (thought it could be long or double, or anything else that int can implicitly cast to)

    public class MyObject
    {      
       public MyObject(): this(123)
       {
       }

       public MyObject(int num)
       {
          //do something with the num
       }
   }

score 0 · Answer 5 · answered Oct 22 '13 at 19:24

0

That means "before you execute what between the curly brackets, execute the suitable Constructor with parameters 123"

answered Oct 22 '13 at 19:24

Orel Eraki

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score 0 · Answer 6 · answered Oct 22 '13 at 19:24

0

The syntax provided is used for "constructor chaining" whereby the specified constructor (which accepts an integer argument) is called before the body of the current constructor.

answered Oct 22 '13 at 19:24

EricLaw

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C# constructor using this

6 Answers6