compare the string in c# .

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4.20/5 (2 votes)

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C#

static void Main(string[] args)
      {
          Object obj = "Int32";
          String s = "Int32";
          String s1 = typeof (int).Name;
          Console.WriteLine("{0}",obj==s);     //true
          Console.WriteLine("{0}", s == s1);  //True
         <big> Console.WriteLine("{0}", obj == s1);//False     *why ???</big>
          Console.ReadLine();
      }

i am not able to understand clearly why the "s1 == obj" is false

what is rule or which basis they are comparing.

Posted 14-Sep-14 22:17pm

siddharth629

Updated 14-Sep-14 22:24pm

v2

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CPallini · Accepted Answer · 2014-09-14T23:45:00

This is a very curious case of outward violation of the transitive property of equality.
I suppose it is due to the nature of C# strings.

C#

Object obj = "Int32";

Here the string is created and 'internalized'. A reference to is is assigned to obj.

C#

String s = "Int32";

Here, the same reference assigned to obj is assigned to s (they 'points' to the same internalized string).

C#

Console.WriteLine("{0}",obj==s);     //true

Here obj and s are compared by reference. The result is true because they both hold the same reference.

C#

Console.WriteLine("{0}", s == s1);  //True

Here s and s1 are compare by value because both are string.

C#

Console.WriteLine("{0}", obj == s1);//False     *why ???

Here obj and s1 are compared by reference and the result is false because they don't hold the same reference.

Shmuel Zang · Accepted Answer · 2014-09-15T00:35:00

In addition to Solution 2, that happens because of a different implementation of the operator ==. While for other reference types, it behaves like ReferenceEquals, for the String class, the Equality Operator is implemented to use the Equals method instead.

When you compare the strings using a reference to an Object, the compiler calls the equality operator of Object (and compares references). When you compare the strings using a reference to a String, the compiler calls the equality operator of String (and compares values).

George Jonsson · Accepted Answer · 2014-09-14T22:32:00

The data type Object is not the same as a String.
It is like comparing a vehicle and a car. A car is a vehicle, but the other way around is not necessarily true.
The same goes for programming. A String inherits from Object, so a String is an Object but an Object could be basically any type.

Try this instead.

C#

Console.WriteLine("{0}", obj.ToString() == s1);

I am not 100% sure, but I think the reason is that for the first two variables, a constant string with the value "Int32" is allocated on the heap. As this string is only allocated once, the comparison
obj == s is true because it is the same string with two different pointers pointing to the same data.

This construct results in a value allocated on the stack.

C#

String s1 = typeof (int).Name;

The comparison s == s1 works because now you compare two string types.

When comparing obj == s1, you try to compare two different types.

This explains it better. String.Intern Method[^]

(My internet connection has been slow, so I might have missed some comments that describes this)

compare the string in c# .

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