Why does “abcd”.StartsWith("ـــــــــــــ") return true?

Asked Feb 13 '19 at 06:24

Active Feb 13 '19 at 07:06

Viewed 78 times

It was really strange for me. The following code returns true for every string. The character is Arabic Tatweel (U+640).

"abcd".StartsWith("ـــــــــــــ") ;//returns true

But when I change the StringComparer to StringComparison.Ordinal it returns false

"abcd".StartsWith("ـــــــــــــ", StringComparison.Ordinal) ;//returns false

Can someone elaborate on the reasons for this behavior and how I could know other characters that may have this behavior?

edited Feb 13 '19 at 07:06

JLRishe

asked Feb 13 '19 at 06:24

Ehsan88

[Not sure if this is a duplicate](https://stackoverflow.com/questions/29831410/why-does-string-startswith-u2d2d-always-return-true). – ProgrammingLlama Feb 13 '19 at 06:28
@John not exactly though – Rahul Feb 13 '19 at 06:37
@Rahul I wasn't really sure, but I thought I'd link it in case it was helpful. – ProgrammingLlama Feb 13 '19 at 06:38
1

@John it's indeed helpful though – Rahul Feb 13 '19 at 06:41
probably because its a Kashida and has no meaning in a word other than justitication – TheGeneral Feb 13 '19 at 06:47
I doubt this is a duplicate at all – TheGeneral Feb 13 '19 at 06:48
Your `ـــــــــــــ` string is a strange one, it is written from right to left. I guess there is some sort of characters that forces `CompareInfo.IsPrefix` method to return `true`. – SᴇM Feb 13 '19 at 06:49
Also note to future readers this is not an underscore its a https://www.fileformat.info/info/unicode/char/0640/index.htm – TheGeneral Feb 13 '19 at 06:52
The character is a `ModifierLetter` according to the `char.GetUnicodeCategory` method. It modifies the previous character. But in the OP's text there is no previous character. I suspect it's being ignored because of that. – Enigmativity Feb 13 '19 at 06:53
yeah its like StartsWith("") – TheGeneral Feb 13 '19 at 06:54
Not directly but related: https://stackoverflow.com/questions/29729391/regular-expression-arabic-characters-and-numbers-only – Alex Yu Feb 13 '19 at 06:59

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