Ruby start_with? inconsistency

Question

Please tell me how the first use of start_with returned false.

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Thanks!

Can you please paste your code into your question instead of the screenshot. Perhaps one of the chars just looks like a `#`, but is actually another uft8 character. — spickermann, Nov 10 '14 at 07:53
the code itself uses a string variable, so i thought it wouldn't be helpful in that way. also, i am very sure it's a number sign. — user3903214, Nov 10 '14 at 07:56
i copy pasted that from the output of the parser i was writing — user3903214, Nov 10 '14 at 07:58
i got `0000000 23 68 6f 77 20 74 6f 20 64 6f 77 6e 6c 6f 61 64` — user3903214, Nov 10 '14 at 08:01
Please set `str =` your string, run `str.start_with?("#")` and `str[0,10].encode('utf-8').chars.each { |c| puts c.ord }` and tell us what you get. — Cary Swoveland, Nov 10 '14 at 08:09
Further to @Jesse's comment, I mean for you to insert `str = ` in front of the troublesome string in your code. What I gave you will tell us what the first 10 Unicode characters in the string are. — Cary Swoveland, Nov 10 '14 at 08:16
@CarySwoveland i got this `["", "#", "h", "o", "w", " ", "t", "o", " ", "d"]` — user3903214, Nov 10 '14 at 08:27
Please check the code you used to get that result. What I gave you includes `puts c.ord`, which prints an integer. — Cary Swoveland, Nov 10 '14 at 08:42
oh yes. i got these: `65279 35 104 111 119 32 116 111 32 100` i solved my problem. thanks for your help! — user3903214, Nov 10 '14 at 08:44
I've just tried to paste the code as text, but unfortunately the BOM is stripped by SO once you submit the change. — Stefan, Nov 10 '14 at 13:03
Unicode 65279 is a 'zero width no-break space' (`U+FEFF`), as @JesseSielaff reports in his answer. — Cary Swoveland, Nov 11 '14 at 03:15

user513951 · Accepted Answer · 2014-11-10T08:57:10.133

Your string may contain a hidden unicode character.

If so, the string starts with that character, not with #, which is why you're getting false.

To see it in Ruby, take the string you're running start_with? on and instead run .unpack('C*'). This will return an array of numbers between 0 and 255, representing the integer values of every byte in the string. Normal printable ASCII characters only go up to 126. Any number higher than that will be a clue that there is a non-printing character hiding in your string.

UPDATE

In this particular case, it turned out that using this diagnostic method showed that there were indeed extra bytes at the beginning of the string. They appeared at the beginning of the array as [239, 187, 191, ...], the string equivalent of which is "\xEF\xBB\xBF" or the UTF-8 codepoint ZERO WIDTH NO-BREAK SPACE, which is inserted as a byte-order mark at the beginning of a file by some text editors.

i got this. how do i interpret this? `[-17, -69, -65, 35, 104, 111, 119, 32, 116, 111, 32, 100, 111, 119, 110, 108, 111, 97, 100, 32, 109, 101, 109, 116, 101, 115, 116, 32, 112, 108, 117, 115, 32, 55, 13, 10]` — user3903214, Nov 10 '14 at 08:08

Ruby start_with? inconsistency

1 Answers1