Checking null and string.Empty in C#

Question

This might sound like a noob question, but are:

string var;
if (var == null)

and

string var;
if (var == string.Empty)

The same?

Duplicate

What's the Difference between String.Empty and Null? and In C#, should I use String.Empty or Null?

Duplicate. I've seen this question before. Sigh, now I have to dive through the depths of SO to find it. — George Stocker, Jan 23 '09 at 02:24
-1 to Gortok (in theory)... Find the dupe before you vote to close! — Jon B, Jan 23 '09 at 02:30
Found it, Jon B: http://stackoverflow.com/questions/151472/what-is-the-difference-between-string-empty-and — George Stocker, Jan 23 '09 at 02:50
http://stackoverflow.com/questions/263191/in-c-should-i-use-string-empty-or-string-empty-or — George Stocker, Jan 23 '09 at 02:50

score 31 · Accepted Answer · edited Jan 23 '09 at 03:51

31

@Jay is correct, they are not the same. String.IsNullOrEmpty() is a convenient method to check for both null and "".

edited Jan 23 '09 at 03:51

Jay Bazuzi

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answered Jan 23 '09 at 02:28

Kevin Tighe

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score 19 · Answer 2 · answered Jan 23 '09 at 02:24

19

No, they are not the same.

string.Empty is the same as "", which is an actual object: a string of 0 length. null means there is no object.

answered Jan 23 '09 at 02:24

Jay Bazuzi

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score 6 · Answer 3 · answered Mar 24 '10 at 14:36

6

they are not the same, the implementation of String.IsNullOrEmpty(string) in mscorlib demonstrate it:

public static bool IsNullOrEmpty(string value)
{
    if (value != null)
    {
        return (value.Length == 0);
    }
    return true;
}

answered Mar 24 '10 at 14:36

Antonio Pelleriti

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sorry, I'm a New User at StackOverflow.com – Antonio Pelleriti Mar 24 '10 at 16:46
+1 for reminding people to go to the source of the code for learning purposes – Matthew Lock Aug 10 '12 at 03:28

score 3 · Answer 4 · answered Jan 23 '09 at 02:30

3

No, they are not. First one checks if the variable has been initialized or if it was set to "null" later. Second one checks if the value of the variable is "" (empty). However, you shouldn't use either. You should use string.IsNullOrEmpty(var) instead.

answered Jan 23 '09 at 02:30

Ilya Volodin

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score 0 · Answer 5 · edited Nov 19 '12 at 11:00

But sometimes you want to know if the string is NULL and it does not matter that its empty (in a OO design). For example you have a method and it will return NULL or a string. you do this because null means the operation failed and an empty string means there is no result.

In some cases you want to know if it failed or if it has no result prior to take any further actions in other objects.

Checking null and string.Empty in C#

Duplicate

5 Answers5