What is the meaning of "this" in C#

Question

Could anyone please explain the meaning "this" in C#?

Such as:

// complex.cs
using System;

public struct Complex 
{
   public int real;
   public int imaginary;

   public Complex(int real, int imaginary) 
   {
      this.real = real;
      this.imaginary = imaginary;
   }

Answer 1

The this keyword is a reference to the current instance of the class.

In your example, this is used to reference the current instance of the class Complex and it removes the ambiguity between int real in the signature of the constructor vs. the public int real; in the class definition.

MSDN has some documentation on this as well which is worth checking out.

Though not directly related to your question, there is another use of this as the first parameter in extension methods. It is used as the first parameter which signifies the instance to use. If one wanted to add a method to the String class you could simple write in any static class

public static string Left(this string input, int length)
{
    // maybe do some error checking if you actually use this
    return input.Substring(0, length); 
}

See also: http://msdn.microsoft.com/en-us/library/bb383977.aspx