Question

To check whether a string is empty I use

var test = string.Empty; 
if (test.Length == 0) Console.WriteLine("String is empty!");
if (!(test.Any())) Console.WriteLine("String is empty!");
if (test.Count() == 0) Console.WriteLine("String is empty!");
if (String.IsNullOrWhiteSpace(test)) Console.WriteLine("String is empty!");

1. All the above statements produces the same output. What is the optimal method that I should use?

   var s = Convert.ToString(test);    
   s = test.ToString(CultureInfo.InvariantCulture);
   

2. Again, both statements does the same thing. What is the best method to use?

I tried debugging and how to benchmark the performance of a C# statement?

Answer 1

First of all the 4 statemens are not giving the same output on all inputs. Try null and the first 3 will throw an exception. And try whithspaces the last one will give you a failty result. So you really have to think about what you want. The best way to go are normally the:

string.IsNullOrEmpty
string.IsNullOrWhiteSpace

Only if you are doing this a few million times you should have a look on how to optimize your code further.

Here some test result, but this can differ on any .net version:

Test results for 100 million iterations:

Equality operator ==:   796 ms 
string.Equals:          811 ms 
string.IsNullOrEmpty:   312 ms 
Length:                 140 ms  [fastest]
Instance Equals:       1077 ms 

source