How to check if a string is null or empty in C#

The String class in the System namespace provides the IsNullOrEmpty() method to check if a string is null or an empty string(""). This is a handy method to validate user input.

IsNullOrEmpty() takes a string as an input and returns a Boolean value that depends on whether or not the string is null or empty.

Syntax

public static bool IsNullOrEmpty (string? value);

The IsNullOrEmpty() method returns true if the input is null.

For example:

string str = null;
Console.WriteLine(String.IsNullOrEmpty(str));  //True

IsNullOrEmpty() returns true if the input is an empty string. In C#, this is a zero length string ("").

For example:

string str1 = "";
string str2 = String.Empty;
Console.WriteLine(String.IsNullOrEmpty(str1)); // True
Console.WriteLine(String.IsNullOrEmpty(str2)); // True

The IsNullOrEmpty() method can be used to avoid the null reference exception by checking if a string is null before using it, as seen below:

if(String.IsNullOrEmpty(userName)) {
  //perform operation on string
}

Code

In the example below, we call the IsNullOrEmpty() method with different string inputs and print the result:

using System;
class HelloWorld
{
    static void Main()
    {
        
        string nullStr = null;
        // print True
        Console.WriteLine(String.IsNullOrEmpty(nullStr));
        string emptyStr1 = "";
        // print True
        Console.WriteLine(String.IsNullOrEmpty(emptyStr1));
        string emptyStr2 = String.Empty;
        // print True
        Console.WriteLine(String.IsNullOrEmpty(emptyStr2));
        string str = "some text";
        // print False
        Console.WriteLine(String.IsNullOrEmpty(str));
    }
}
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