C# tip: String.IsNullOrEmpty or String.IsNullOrWhiteSpace?

Imagine this: you have created a method that creates a new user in your system, like this:

void CreateUser(string username)
{
    if (string.IsNullOrEmpty(username))
        throw new ArgumentException("Username cannot be empty");

    CreateUserOnDb(username);
}

void CreateUserOnDb(string username)
{
    Console.WriteLine("Created");
}

It looks quite safe, right? Is the first check enough?

Let's try it: CreateUser("Loki") prints Created, while CreateUser(null) and CreateUser("") throw an exception.

What about CreateUser(" ")?

Unfortunately, it prints Created: this happens because the string is not actually empty, but it is composed of invisible characters.

The same happens with escaped characters too!

To avoid it, you can replace String.IsNullOrEmpty with String.IsNullOrWhiteSpace: this method performs its checks on invisible characters too.

So we have:

String.IsNullOrEmpty(""); //True
String.IsNullOrEmpty(null); //True
String.IsNullOrEmpty("   "); //False
String.IsNullOrEmpty("\n"); //False
String.IsNullOrEmpty("\t"); //False
String.IsNullOrEmpty("hello"); //False

but also

String.IsNullOrWhiteSpace("");//True
String.IsNullOrWhiteSpace(null);//True
String.IsNullOrWhiteSpace("   ");//True
String.IsNullOrWhiteSpace("\n");//True
String.IsNullOrWhiteSpace("\t");//True
String.IsNullOrWhiteSpace("hello");//False

As you can see, the two methods behave in a different way.

If we want to see the results in a tabular way, we have:

Conclusion

Do you have to replace all String.IsNullOrEmpty with String.IsNullOrWhiteSpace? Probably yes, unless you have a specific reason to consider the latest three values in the table as valid characters.

More on this topic can be found here

👉 Let's discuss about it on Twitter or on the comment section below.

Published under CSharp, CSharp Tip on 06 July, 2021.