How can I check whether a string variable is empty or null in C#?

Question

How can I check whether a C# variable is an empty string "" or null?

I am looking for the simplest way to do this check. I have a variable that can be equal to "" or null. Is there a single function that can check if it's not "" or null?

Solution 1

if (string.IsNullOrEmpty(myString)) {
   //
}

Solution 2

Since .NET 2.0 you can use:

// Indicates whether the specified string is null or an Empty string.
string.IsNullOrEmpty(string value);

Additionally, since .NET 4.0 there's a new method that goes a bit farther:

// Indicates whether a specified string is null, empty, or consists only of white-space characters.
string.IsNullOrWhiteSpace(string value);

Solution 3

if the variable is a string

bool result = string.IsNullOrEmpty(variableToTest);

if you only have an object which may or may not contain a string then

bool result = string.IsNullOrEmpty(variableToTest as string);

Solution 4

Cheap trick:

Convert.ToString((object)stringVar) == ""

This works because Convert.ToString(object) returns an empty string if object is null. Convert.ToString(string) returns null if string is null.

(Or, if you're using .NET 2.0 you could always using String.IsNullOrEmpty.)

Solution 5

if (string.IsNullOrEmpty(myString)) 
{
  . . .
  . . .
}

View more solutions

Comments

[Adam Houldsworth]

While technically correct I can categorically say I have never seen this method used.

[molnarm]

I had the same problem and the second one doesn't work correctly. Try this: object x=3; bool result = string.IsNullOrEmpty(x as string); 'x as string' will be null so the result is true despite x having a value other than null or an empty string. I didn't find a short solution, used a double check.

[jk.]

@MártonMolnár it would have to contain a string 3 is not a string so this is expected try using "3" instead

[Shaiju T]

when i use IsEmpty it says: 'string' does not contain a definition for IsEmpty , can i use IsEmpty in msdn or should i use IsNullOrEmpty ?

[Andrew Liu]

Very simple and useful. I wish PHP could have something like this

[Milan]

@Lion Liu: Actually I think PHP has exactly as much to offer. See: php.net/manual/en/function.empty.php

[Tony Trembath-Drake]

I like IsNullOrWhiteSpace (null,empty, or whitespace...)

[Stokely]

Are we to assume that this conversion of stringVar to a cast object returns empty string for both null and empty string assigned to the stringVar variable, but converting the same stringVar without the cast returns null and empty string instead? Im just trying to find out all the variations.....

[chadpeppers]

@AndrewLiu there is you simple do if (empty($my_var))

[kayleeFrye_onDeck]

Just to be super-clear, you have to use the class function for string/String, NOT trying to use the function via the object! Eg, string foo; will not allow you to do foo.IsNullOrEmpty();; you need to use it like string.IsNullOrEmpty(foo); This is kind of annoying when coming from other languages that have built in null/0-length-checks for their string objects.

[Momoro]

stom, your question was unclear. You just said IsEmpty, but that is not a valid variable in the .NET C#