Check if string is empty or all spaces in C#

Question

How to easily check if a string is blank or full of an undetermined amount of spaces, or not?

Solution 1

If you have .NET 4, use the string.IsNullOrWhiteSpace method:

if(string.IsNullOrWhiteSpace(myStringValue))
{
    // ...
}

If you don't have .NET 4, and you can stand to trim your strings, you could trim it first, then check if it is empty.

Otherwise, you could look into implementing it yourself:

.Net 3.5 Implementation of String.IsNullOrWhitespace with Code Contracts

Solution 2

If it's already known to you that the string is not null, and you just want to make sure it's not a blank string use the following:

public static bool IsEmptyOrWhiteSpace(this string value) =>
  value.All(char.IsWhiteSpace);

Solution 3

If you literally need to know if the "string is blank or full of an undetermined amount of spaces", use LINQ as @Sonia_yt suggests, but use All() to ensure that you efficiently short-circuit out as soon as you've found a non-space.

(This is give or take the same as Shimmy's, but answers the OP's question as written to only check for spaces, not any and all whitespace -- \t, \n, \r, etc.)

/// <summary>
/// Ensure that the string is either the empty string `""` or contains
/// *ONLY SPACES* without any other character OR whitespace type.
/// </summary>
/// <param name="str">The string to check.</param>
/// <returns>`true` if string is empty or only made up of spaces. Otherwise `false`.</returns>
public static bool IsEmptyOrAllSpaces(this string str)
{
    return null != str && str.All(c => c.Equals(' '));
}

And to test it in a console app...

Console.WriteLine("    ".IsEmptyOrAllSpaces());      // true
Console.WriteLine("".IsEmptyOrAllSpaces());          // true
Console.WriteLine("  BOO  ".IsEmptyOrAllSpaces());   // false

string testMe = null;
Console.WriteLine(testMe.IsEmptyOrAllSpaces());      // false

Comments

[sylverfyre]

I believe in new versions it's string.IsNullOrEmpty(YourString)

[Merlyn Morgan-Graham]

@sylverfyre: Nope. They're two different methods and do different things. See: IsNullOrEmpty vs IsNullOrWhiteSpace

[Simon Bergot]

This answer is incorrect as it will return true if the string is null.

[Merlyn Morgan-Graham]

@Simon: If people to whom this difference is important can't figure that out from the name of the method, then I probably can't help them

[Palec]

If you need to check for null and reject it, use null-conditional invocation and null-coalescing: value?.All(char.IsWhiteSpace) ?? false — or you can employ less fancy short-circuit evaluation: value != null && value.All(char.IsWhiteSpace)

[Palec]

Too chatty and ill-performing to be useful. This always iterates the whole string, even after seeing a non-space char. Enumerable.All<TSource> employs short-circuit evaluation, see .NET reference source.

[ruffin]

Can't help them? No, @Simon is right; sure you can! if (string.IsNullOrWhiteSpace(myStringValue) && null != myStringValue). Maybe show how to create an extension method IsWhiteSpaceAndNotNull. Unfortunately, strictly speaking, this answer lets non-spaces in, so it doesn't precisely answer the OP's question as written.

[Merlyn Morgan-Graham]

@ruffin I believe the additions you are proposing would bloat this answer unnecessarily, wouldn't be a good pay-off, and wouldn't be doing copy-pasta coders any favors. You're free to add your own answer and find out.

[ruffin]

And done. ;^D The OP probably wanted what you provided (we may never know...), but taken literally, your answer lets in null, \t, \r, and \n, which aren't spaces. /shrug Though this basically dupes Shimmy's, adding the ability to test nulls, which extension methods can't do.

[Merlyn Morgan-Graham]

"but you can't call an extension method on nulls" are you sure? did you try it? I'm about 80% certain you can, without issue, as long as you do null checks before access. It's just syntactic sugar for a static method after all.

[Palec]

!enumerable.Any(x => !predicate(x)) = enumerable.All(x => predicate(x)) Just convoluted thinking.

[ruffin]

@MerlynMorgan-Graham You're quite right. I'm used to string testMe = null; testMe.IndexOf("spam"); and getting An unhandled exception of type 'System.NullReferenceException' occurred, but that's the "fault" of IndexOf, not that the string was null. Score one for cargo culting/elephant whistles. "Hey, calling string functions like IndexOf on null strings breaks. Better not use extension methods on null strings. [Using extension methods on non-null strings never breaks.] See?!" (◔_◔)

[ruffin]

@Palec Yeah, Shimmy's use of All is better, but his answer also makes the same "mistake" as Merlyn's... the set of whitespace characters > the set of space characters. ;^) I'll edit to use All. The double negative looked odd when I was writing it, and I just added a comment instead of figuring out The Right Thing To Do... Fail. Just wanted to quickly show checking for null wasn't a huge burden, which Merlyn seemed to suggest it was. /shrug Thanks for the catch.