Easier way of writing null or empty in C#?

Question

I'm sure I've missed something here. With a certain project I need to check if a string is null or empty.

Is there an easier way of writing this?

if (myString == null || myString == "")
{
   ...

Hands

Answer 1

Yes, there's the String.IsNullOrEmpty helper method for exactly this already:

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

Pancratium

And on a relate note: #2552850 – Compander

Just to be super-clear, you need 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, since you can't safely do something like, if(foo.Length == 0) because that can trigger an exception. – Cursorial

@kayleeFrye_onDeck: You should be able to use if (foo?.Length ?? 0 == 0), but in general, calling an instance method requires a non-null reference. You can fake this with extension methods that don't check their argument, but I think that's frowned upon, as extension methods should behave as if they were instance methods. – Pancratium

That's some strange syntax o_o I'm not a C# developer, just someone who happens to use it once in a while to develop modules with it ad-hoc but I can't say I've seen anything like that before... I get what it's doing, just wished I knew about it sooner! – Cursorial

Answer 2

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

Or you could take advantage of a quirk in extension methods, they allow this to be null:

static class Extensions {
    public static bool IsEmpty(this string s) {
        return string.IsNullOrEmpty(s);
    }
}

which then lets you write:

if (myString.IsEmpty()) {
  ...
}

Although you probably should pick another name than 'empty'.

Kayleen

Nice example of extension methods! Thanks! – Hands

Why not string.IsNullOrEmpty(s) instead of s == null || s == string.Empty? – Rental

Answer 3

If you are on .NET 4, you can use

if(string.IsNullOrWhiteSpace(myString)){

}

else:

if(string.IsNullOrEmpty(myString)){

}

Rollo

IsNullOrWhiteSpace checks for something else than being equal to "" so it'd have different semantics than the code snippet in the question. – Pancratium

Answer 4

To avoid null checks you can use ?? operator.

var result = value ?? "";

I often use it as guards to avoid sending in data that I don't want in methods.

JoinStrings(value1 ?? "", value2 ?? "")

It can also be used to avoid unwanted formatting.

string ToString()
{
    return "[" + (value1 ?? 0.0) + ", " + (value2 ?? 0.0) + "]";
}

This can also be used in if statements, it's not so nice but can be handy sometimes.

if (value ?? "" != "") // Not the best example.
{
}

Kaffir

?? can be used to avoid null check but not for "". "" ?? anything" still yeilds to "" – Aluminum

Answer 5

In c# 9 by using pattern matching you could do the following

myString is not {Length: > 0}; // Equivalent to string.IsNullOrEmpty(myString)

Changchangaris

Honestly? I don't like it.. "myString is not an object with a length property that is greater than zero" - this is a negative flavored test (like a test for success being if(!operationFailed) - negative flavored / if(operationSucceeded) - positive flavor). You have to stop and think about what it actually means/what the author intended so it reduces code readability/glanceability/self-documentation. IsNullOrEmpty does a really good job of explaining what it does. – Bamboozle

It might be not so great for readability but it's a feature of the language now – Changchangaris

Answer 6

C# 9's pattern matching allows you to write:

myString is null or ""

Bamboozle

Answer 7

// if the string is not defined to null then IsNullOrEmpty it works great but if string is defined null then trim will throw exception.

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

//you can use IsNullOrWhiteSpace which work well for multiple white space in string .i.e it return true for multiple white space also

 if(string.IsNullOrWhiteSpace (myString.Trim()){
     ...
    }

Macnamara

"Trim" is not a standalone function, it is an instance method of String. Proper usage: myString.Trim(), but that blows up when mystring is null. Use String.IsNullOrWhiteSpace() – Algometer

i agree with you, so i have corrected in above code. Thanks @HansKesting – Macnamara