In the C# language, strings can be either equal to the null: meaning they don't reference any data, or empty: meaning they reference a character buffer is 0 characters long. C# Developers frequently need to see if a string contains no characters(null or empty). Here in IT-Interview.com, we see how you can check for empty strings in the C# programming language and compare the performance of each approach.

5 Ways to Check Empty String in C#
1. if(a=="")
2. if(string.Equals(a, ""))
3. if(string.IsNullOrEmpty(a))
4. if(a.Length==0)
5. if(a.Equals(""))

Program:
private void Page_Load(object sender, System.EventArgs e)
  {
   string a="";
   for(int i=0;i<=1000000;i++)
   {
    if(a=="")
    //if(string.Equals(a, ""))   
    //if(string.IsNullOrEmpty(a))
    //if(a.Length==0)
    //if(a.Equals(""))
    {
    }
   }
  }
 
Performance Result:
if(a=="")           : 796 ms
if(string.Equals(a, ""))   : 811 ms
if(string.IsNullOrEmpty(a))  : 312 ms
if(a.Length==0)        : 140 ms  [fastest]
if(a.Equals(""))       : 1077 ms

Comparison and Explanation:
1. if(a=="")
  Uses Equals operator
  Pro: For many developers, this is the clearest code,
  Con: It is not the fastest

2. if(string.Equals(a, ""))
  Static Equals method, This has the same semantics as 1 but uses different syntax.If you look at == in MSIL, it is called op_Equality.
  Pro: No
  Con: It is not the fastest

3. if(string.IsNullOrEmpty(a))
  Using string.IsNullOrEmpty
   Pro: IsNullOrEmpty detects both of these conditions at the same time. By using string.IsNullOrEmpty, the code for it is much clearer, which is a huge positive. What we found is that string.IsNullOrEmpty is about in the middle in performance.
   Con: IsNullOrEmpty is a newer static method that wasn't present in the first releases of .NET. 

4. if(a.Length==0)
  Using string length check 
  Pro: Best performance
  Con: However, it throws a NullReferenceException when the string is null. Null strings occur often in programs.

5. if(a.Equals(""))
  Instance Equals method
   Pro: No
   Con: Worst performance.This calling pattern is different because the compiler must know the string s is not null before calling the method. This changes the performance somewhat.

Conclusion:
string.IsNullOrEmpty is highly highly recommended by IT Interview if you are using .NET 2.0 and above.

Provided by: csharpro  on: Sep 24, 2009  

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