Check if an NSString is just made out of spaces

Question

I want to check if a particular string is just made up of spaces. It could be any number of spaces, including zero. What is the best way to determine that?

Solution 1

NSString *str = @"         ";
NSCharacterSet *set = [NSCharacterSet whitespaceCharacterSet];
if ([[str stringByTrimmingCharactersInSet: set] length] == 0)
{
    // String contains only whitespace.
}

Solution 2

Try stripping it of spaces and comparing it to @"":

NSString *probablyEmpty = [myString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
BOOL wereOnlySpaces = [probablyEmpty isEqualToString:@""];

Solution 3

It's significantly faster to check for the range of non-whitespace characters instead of trimming the entire string.

NSCharacterSet *inverted = [[NSCharacterSet whitespaceAndNewlineCharacterSet] invertedSet];
NSRange range = [string rangeOfCharacterFromSet:inverted];
BOOL empty = (range.location == NSNotFound);

Note that "filled" is probably the most common case with a mix of spaces and text.

testSpeedOfSearchFilled - 0.012 sec
testSpeedOfTrimFilled - 0.475 sec
testSpeedOfSearchEmpty - 1.794 sec
testSpeedOfTrimEmpty - 3.032 sec

Tests run on my iPhone 6+. Code here. Paste into any XCTestCase subclass.

Solution 4

Try this:

[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

or

[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

Solution 5

I'm really surprised that I am the first who suggests Regular Expression

NSString *string = @"         ";
NSString *pattern = @"^\\s*$";
NSRegularExpression *expression = [[NSRegularExpression alloc] initWithPattern:pattern options:0 error:nil];
NSArray *matches = [expression matchesInString:string options:0 range:NSMakeRange(0, string.length)];
BOOL isOnlyWhitespace = matches.count;

Or in Swift:

let string = "         "
let pattern = "^\\s*$"
let expression = try! NSRegularExpression(pattern:pattern)
let matches = expression.matches(in: string, range: NSRange(string.startIndex..., in: string))
let isOnlyWhitespace = !matches.isEmpty

Alternatively

let string = "         "
let isOnlyWhitespace = string.range(of: "^\\s*$", options: .regularExpression) != nil

View more solutions

Comments

[BoltClock]

Depending on the situation one may want to use whitespaceAndNewlineCharacterSet instead (does exactly what it says on the tin).

[Alexsander Akers]

This is an NSMutableString method.

[picciano]

Um, no it's not. It returns a new NSString and is declared in NSString.h.

[Alexsander Akers]

Actually it isn't defined anywhere.