difference between string.empty and string="" c#

In .Net Pre 2.0  "" creates an object

while string.empty creates no object .So it is more efficient to use string.Empty 

String.Empty is not a Constant .Its a Static readonly Field .If it was a constant there would be no diffence between "" and string.empty

String.Empty is a static readonly field of the System.String class.

When the String class is first accessed, its static constructor sets its Empty field equal to the string literal "".

So, Sivaraman is correct that they both represent an empty string i.e. a string which contains no characters, not even '\0', and so has a Length of zero.

However, they are treated differently by the compiler in that "" is a constant but String.Empty is not. You can see this by trying to compile the following program:

using System;

class Test

{  

   static void  Main()

   {

     const string s1 = "";

     const string s2 = String.Empty;

   }

}

The error message is :

error CS0133: The expression being assigned to 's2' must be constant

Notice also that strings are always followed in memory by a null character ('\0') even though this null character is not part of the string itself. This enables you to iterate through the characters of a string using a pointer in 'unsafe' code, though there can be problems if the string itself contains embedded nulls.