This content originally appeared on DEV Community and was authored by Mariem Moalla
When working with text in .NET, one of the most common checks we perform is:
“Does this string have a meaningful value, or is it just empty/null?”
Two helpers exist for this purpose:
- string.IsNullOrEmpty
- string.IsNullOrWhiteSpace At first glance, they may seem similar, but there’s an important distinction that can save you from getting bugs.
Using string.IsNullOrEmpty
This method checks if a string is either:
- null
- "" (an empty string)
Console.WriteLine(string.IsNullOrEmpty(null)); // true
Console.WriteLine(string.IsNullOrEmpty("")); // true
Console.WriteLine(string.IsNullOrEmpty(" ")); // false
Console.WriteLine(string.IsNullOrEmpty("abc")); // false
Notice that " " (spaces only) returns false.
This means IsNullOrEmpty only guards against null or empty strings, not whitespace.
Using string.IsNullOrWhiteSpace
This method goes one step further: it considers whitespace-only strings as invalid.
Console.WriteLine(string.IsNullOrWhiteSpace(null)); // true
Console.WriteLine(string.IsNullOrWhiteSpace("")); // true
Console.WriteLine(string.IsNullOrWhiteSpace(" ")); // true
Console.WriteLine(string.IsNullOrWhiteSpace("abc")); // false
Here, " " returns true because the method trims out whitespace and checks for emptiness.
Performance Consideration
Both methods are O(n) because they may scan characters (especially IsNullOrWhiteSpace).
- IsNullOrEmpty is slightly faster since it only checks length.
- IsNullOrWhiteSpace is marginally slower but usually negligible in real-world apps.
For example:
var str = new string(' ', 1000); // 1000 spaces
Console.WriteLine(string.IsNullOrEmpty(str)); // false
Console.WriteLine(string.IsNullOrWhiteSpace(str)); // true
The performance difference only matters when doing millions of checks per second, which is rare in typical business applications.
This content originally appeared on DEV Community and was authored by Mariem Moalla
Mariem Moalla | Sciencx (2025-10-03T10:45:37+00:00) C# tips: string.IsNullOrEmpty vs string.IsNullOrWhiteSpace. Retrieved from https://www.scien.cx/2025/10/03/c-tips-string-isnullorempty-vs-string-isnullorwhitespace/
Please log in to upload a file.
There are no updates yet.
Click the Upload button above to add an update.