Difference between IsNullOrEmpty and IsNullOrWhiteSpace in C#

Question

What are differences between these commands in C#

string text= "  ";
1-string.IsNullOrEmpty(text.Trim())

2-string.IsNullOrWhiteSpace(text)

refer to :http://msdn.microsoft.com/en-us/library/system.string.isnullorempty.aspx and http://msdn.microsoft.com/en-us/library/system.string.isnullorwhitespace.aspx — ojlovecd, Sep 10 '13 at 04:21
"`IsNullOrWhiteSpace` covers `IsNullOrEmpty`" (see TGH answer). — samus, Aug 23 '17 at 16:32

score 254 · Accepted Answer · edited Aug 29 '17 at 10:27

254

Source: MSDN

IsNullOrWhiteSpace is a convenience method that is similar to the following code, except that it offers superior performance:
return String.IsNullOrEmpty(value) || value.Trim().Length == 0;
White-space characters are defined by the Unicode standard. The IsNullOrWhiteSpace method interprets any character that returns a value of true when it is passed to the Char.IsWhiteSpace method as a white-space character.

edited Aug 29 '17 at 10:27

shA.t

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answered Sep 10 '13 at 04:21

fionbio

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Actually the trimmed string length test will also catch empty strings, so – galaxis Sep 26 '21 at 19:45

fubo · Answer 2 · 2021-12-07T09:50:19.690

Short answer:

In common use, space " ", Tab "\t" and newline "\n" are the difference:

string.IsNullOrWhiteSpace("\t"); //true
string.IsNullOrEmpty("\t"); //false

string.IsNullOrWhiteSpace(" "); //true
string.IsNullOrEmpty(" "); //false

string.IsNullOrWhiteSpace("\n"); //true
string.IsNullOrEmpty("\n"); //false

https://dotnetfiddle.net/4hkpKM

also see this answer about: whitespace characters

Long answer:

There are also a few other white space characters, you probably never used before

Members of the UnicodeCategory.SpaceSeparator category, which includes the characters SPACE (U+0020), NO-BREAK SPACE (U+00A0), OGHAM SPACE MARK (U+1680), EN QUAD (U+2000), EM QUAD (U+2001), EN SPACE (U+2002), EM SPACE (U+2003), THREE-PER-EM SPACE (U+2004), FOUR-PER-EM SPACE (U+2005), SIX-PER-EM SPACE (U+2006), FIGURE SPACE (U+2007), PUNCTUATION SPACE (U+2008), THIN SPACE (U+2009), HAIR SPACE (U+200A), NARROW NO-BREAK SPACE (U+202F), MEDIUM MATHEMATICAL SPACE (U+205F), and IDEOGRAPHIC SPACE (U+3000).
Members of the UnicodeCategory.LineSeparator category, which consists solely of the LINE SEPARATOR character (U+2028).
Members of the UnicodeCategory.ParagraphSeparator category, which consists solely of the PARAGRAPH SEPARATOR character (U+2029).
The characters CHARACTER TABULATION (U+0009), LINE FEED (U+000A), LINE TABULATION (U+000B), FORM FEED (U+000C), CARRIAGE RETURN (U+000D), and NEXT LINE (U+0085).

https://learn.microsoft.com/en-us/dotnet/api/system.char.iswhitespace

What about `string.IsNullOrWhiteSpace("")` ? – samus Aug 23 '17 at 16:18 — samus, Aug 23 '17 at 16:18
@samusarin no difference https://dotnetfiddle.net/9uWpvh – fubo Aug 24 '17 at 05:18 — fubo, Aug 24 '17 at 05:18

score 62 · Answer 3 · edited Sep 09 '21 at 07:48

62

The first method checks if a string is null or a blank string. In your example you can risk a null reference since you are not checking for null before trimming

1- string.IsNullOrEmpty(text.Trim())

The second method checks if a string is null or an arbitrary number of spaces in the string (including a blank string)

2- string .IsNullOrWhiteSpace(text)

The method IsNullOrWhiteSpace covers IsNullOrEmpty, but it also returns true if the string contains only white space characters.

In your concrete example you should use 2) as you run the risk of a null reference exception in approach 1) since you're calling trim on a string that may be null

edited Sep 09 '21 at 07:48

Kevin

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answered Sep 10 '13 at 04:21

TGH

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with c#6 you can do `string.IsNullOrEmpty(text?.Trim())` safely – goldenratio May 12 '19 at 04:50
So its always better to use `IsNullOrWhiteSpace` than `IsNullOrEmpty` ? – Shaiju T Oct 29 '20 at 10:37

Ľuboš Pilka · Answer 4 · 2019-04-23T14:29:02.573

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This is implementation of methods after decompiling.

    public static bool IsNullOrEmpty(String value) 
    {
        return (value == null || value.Length == 0); 
    }

    public static bool IsNullOrWhiteSpace(String value) 
    {
        if (value == null) return true; 

        for(int i = 0; i < value.Length; i++) { 
            if(!Char.IsWhiteSpace(value[i])) return false; 
        }

        return true;
    }

So it is obvious that IsNullOrWhiteSpace method also checks if value that is being passed contain white spaces.

Whitespaces refer : https://msdn.microsoft.com/en-us/library/system.char.iswhitespace(v=vs.110).aspx

edited Apr 23 '19 at 14:29

answered Oct 24 '16 at 10:09

Ľuboš Pilka

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Nice, : ) How did you decompile to look at the implementation ? – Shaiju T Oct 29 '20 at 11:08
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Using decompiler like dotpeek – Ľuboš Pilka Oct 30 '20 at 10:20

score 12 · Answer 5 · edited Aug 16 '14 at 12:53

String.IsNullOrEmpty(string value) returns true if the string is null or empty. For reference an empty string is represented by "" (two double quote characters)

String.IsNullOrWhitespace(string value) returns true if the string is null, empty, or contains only whitespace characters such as a space or tab.

To see what characters count as whitespace consult this link: http://msdn.microsoft.com/en-us/library/t809ektx.aspx

score 4 · Answer 6 · answered Oct 24 '16 at 09:49

If your string (In your case the variable text) could be null this would make a big Difference:

1-string.IsNullOrEmpty(text.Trim()) --> EXCEPTION since your calling a mthode of a null object

2-string.IsNullOrWhiteSpace(text) This would work fine since the null issue is beeing checked internally

To provide the same behaviour using the 1st Option you would have to check somehow if its not null first then use the trim() method

if ((text != null) && string.IsNullOrEmpty(text.Trim())) { ... }

score 3 · Answer 7 · edited Aug 17 '21 at 17:47

3

String.IsNullOrWhiteSpace(text) should be used in most cases as it also includes a blank strings with whitespaces but no other text.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            var str = "";
            
            Console.WriteLine(string.IsNullOrWhiteSpace(str));              
            
        }
    }
}

It returns True!

edited Aug 17 '21 at 17:47

evandrix

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answered May 23 '17 at 08:16

vibs2006

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Your example is not correct since `string.IsNullOrEmpty` will return true for variable `str`. – Azimuth Dec 10 '18 at 13:42
@Azimuth I'm not able to understand properly. Can you please create a fiddle on https://rextester.com/ or any other C# online Fiddle Tool that you prefer? – vibs2006 Dec 11 '18 at 07:07
why should I provide some fiddle? Just replace `IsNullOrWhiteSpace` with `IsNullOrEmpty` in your code and run it. It will return `true`. Thus, your example doesn't show the difference between `IsNullOrWhiteSpace` and `IsNullOrEmpty`. – Azimuth Dec 11 '18 at 08:31
sure I'll do that. Thanks @Azimuth for explaining. – vibs2006 Dec 11 '18 at 10:02
string.IsNullOrWhiteSpace returns this expression String.IsNullOrEmpty(value) || value.Trim().Length == 0; So, use it in textbox of entry(xamarin) validation handlers – Sachintha Udara Jan 09 '19 at 08:30

score 1 · Answer 8 · answered Jan 19 '18 at 00:47

[Performance Test] just in case anyone is wondering, in a stopwatch test comparing

if(nopass.Trim().Length > 0)

if (!string.IsNullOrWhiteSpace(nopass))

these were the results:

Trim-Length with empty value = 15

Trim-Length with not empty value = 52

IsNullOrWhiteSpace with empty value = 11

IsNullOrWhiteSpace with not empty value = 12

Difference between IsNullOrEmpty and IsNullOrWhiteSpace in C#

8 Answers8