How to parse NSString into BOOL in Objective-C?

Question

I am programming in Objective-C for iOS. I would like to parse an object of type NSString into a scalar of type BOOL.

I have a value, and I know that it will either be @"YES" or @"NO", but that YES (or) NO value is NSString and I just want to change NSString into BOOL.

How can I do that?

Please answer me if you know.

Thanks for reading.

score 157 · Accepted Answer · answered Jan 17 '12 at 16:32

157

I think it's this:

BOOL boolValue = [myString boolValue];

answered Jan 17 '12 at 16:32

bschultz

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what will be the boolValue of "Abdul"? Please suggest me. – Abdul Yasin Mar 04 '14 at 10:19
3

@Abdul Yasin, it will be 0/false. This method is only effective if you know there is a boolean value in the string; e.g. @"1", @"true", @"YES" etc. Other than these, boolValue will always return 0; – x4h1d Jul 16 '14 at 09:29
@x4h1d Thanks. I really appreciate your feedback – Abdul Yasin Jul 16 '14 at 09:32
And why `string 0` gives me `nil`, @x4h1d? – new2ios Jul 13 '15 at 14:32
@new2ios, `[@"string 0" boolValue]` returns `0`, not `nil`, as I said. You can try it using: `NSLog(@"%zd", [@"string 0" boolValue]);` in __Objective C__ or `let str: NSString = "string 0" println(str.boolValue)` in __Swift__. – x4h1d Jul 13 '15 at 15:34
Sorry, I don't explained well - I mean `[@"0" boolValue]` returns `nil`, @x4h1d. I have expression which returns string 0 (`@"0"`). When I convert it to `BOOL` using `boolValue` I get `nil`. – new2ios Jul 13 '15 at 15:36
@new2ios, are you sure? Because I just tested `[@"0" boolValue]` on both language and it returns as expected. FYI, make sure you use `%zd` to print boolValue. – x4h1d Jul 13 '15 at 15:44
1

:) it's okay. `po` means `print object` and `boolValue` is clearly not an object. – x4h1d Jul 13 '15 at 15:50

score 22 · Answer 2 · answered Jan 17 '12 at 16:32

You should probably use NSString's -boolValue. To quote the documentation directly:

[Returns t]he Boolean value of the receiver’s text. Returns YES on encountering one of "Y", "y", "T", "t", or a digit 1-9—the method ignores any trailing characters. Returns NO if the receiver doesn’t begin with a valid decimal text representation of a number.

That would seem to match your input cases.

score 2 · Answer 3 · answered Jan 17 '12 at 16:32

2

if ([string isEqualToString: @"YES"])
  foo();
else
  bar();

answered Jan 17 '12 at 16:32

LOL u beat me by 6 seconds! haha – Steve Jan 17 '12 at 16:32
1

That's not the right way. See the other two answers by bschultz and Tommy. – Jan 17 '12 at 16:34
3

@H2CO3, eh. The OP said `I exactly know the return value` so I wouldn't go so far as to say it was wrong. Although I agree that `boolValue` seems more robust - and possibly faster by virtue of only needing to inspect the first character... but still. – Steve Jan 17 '12 at 16:37

score 0 · Answer 4 · answered Jul 15 '15 at 11:27

This property should also return true if string is 'true' that's why i think extension is needed...

extension NSString{
 var boolValueExtended: Bool {
    get{
        return boolValue ||
            self.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet()).uppercaseString == "TRUE"
    }
}

}

score 0 · Answer 5 · answered Jan 17 '12 at 16:34

0

This would probably best be solved with a conditional, for example:

if ([myString isEqualToString:@"YES"])
    myBool = YES;
else if ([myString isEqualToString:@"NO"])
    myBool = NO;

Hope this helped you, good luck with your programming.

answered Jan 17 '12 at 16:34

Marcus Buffett

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This solution is far from correct. There are numerous ways to store a bool in a string, and this only handles a very specific one. Why duplicate the functionality of a method that's already implemented. – FreeAsInBeer Mar 16 '12 at 13:14
This is too dirty way. – AlKozin Jan 16 '14 at 10:22

How to parse NSString into BOOL in Objective-C?

5 Answers5