C# Copy() Method

The String.Copy() method in C# creates a new string instance with the same value as the specified string. While strings are immutable in C#, this method ensures you get a completely separate string object in memory, which can be useful in certain scenarios involving string interning.

Syntax

Following is the syntax for the String.Copy() method −

public static string Copy(string str);

Parameters

• str − The string to copy. Cannot be null.

Return Value

Returns a new string with the same value as the input string but as a separate object in memory.

Using String.Copy() for Basic Copying

Example

using System;
public class Demo {
   public static void Main(string[] args) {
      string s1 = "Amy";
      string s2 = "Katie";
      string s3 = String.Copy(s2);
      Console.WriteLine("String1 = " + s1);
      Console.WriteLine("String2 = " + s2);
      Console.WriteLine("String3 (copy of s2) = " + s3);
      Console.WriteLine("Are s1 and s2 equal? = " + s1.Equals(s2));
      Console.WriteLine("Are s2 and s3 equal? = " + s2.Equals(s3));
      Console.WriteLine("CompareOrdinal(s1, s2): " + string.CompareOrdinal(s1, s2));
      Console.WriteLine("CompareOrdinal(s2, s3): " + string.CompareOrdinal(s2, s3));
   }
}

The output of the above code is −

String1 = Amy
String2 = Katie
String3 (copy of s2) = Katie
Are s1 and s2 equal? = False
Are s2 and s3 equal? = True
CompareOrdinal(s1, s2): -10
CompareOrdinal(s2, s3): 0

Understanding Object Independence

Example

using System;
public class Demo {
   public static void Main(string[] args) {
      string s1 = "Gary";
      string s2 = "Gary";
      string s3 = String.Copy(s2);
      Console.WriteLine("String1 = " + s1);
      Console.WriteLine("String2 = " + s2);
      Console.WriteLine("String3 (copy) = " + s3);
      Console.WriteLine("Is s1 and s2 equal? = " + s1.Equals(s2));
      Console.WriteLine("Is s2 and s3 equal? = " + s2.Equals(s3));
      
      // Reassign s3 to demonstrate independence
      s3 = "Harry";
      Console.WriteLine("After changing s3 to 'Harry':");
      Console.WriteLine("Is s2 and s3 equal? = " + s2.Equals(s3));
      Console.WriteLine("s2 remains: " + s2);
   }
}

The output of the above code is −

String1 = Gary
String2 = Gary
String3 (copy) = Gary
Is s1 and s2 equal? = True
Is s2 and s3 equal? = True
After changing s3 to 'Harry':
Is s2 and s3 equal? = False
s2 remains: Gary

When to Use String.Copy()

The String.Copy() method is rarely needed in modern C# programming because string assignment already creates independent references due to string immutability. However, it can be useful when working with string interning scenarios or when you specifically need to ensure a new string object in memory.

Example with Reference Comparison

using System;
public class Demo {
   public static void Main(string[] args) {
      string original = "Hello World";
      string copied = String.Copy(original);
      
      Console.WriteLine("Content comparison: " + original.Equals(copied));
      Console.WriteLine("Reference comparison: " + ReferenceEquals(original, copied));
      Console.WriteLine("Original: " + original);
      Console.WriteLine("Copied: " + copied);
   }
}

The output of the above code is −

Content comparison: True
Reference comparison: False
Original: Hello World
Copied: Hello World

Conclusion

The String.Copy() method creates a new string instance with identical content but different memory location. While rarely needed due to string immutability in C#, it ensures complete object independence when required in specific scenarios involving string interning or memory management.