如何从NSString中删除隐藏的字符？

Question

After copying pasting a text from the web, in my mac app NSTextArea, I see

EE

If I copy these 2 letters in a browser I see:

E?E

If I copy them in google translator I get

E 'E

I cannot identify this character in between the two E. But the question is: how do I remove these hidden characters from my NSString?

Answer 1

In your uploaded file the specific hex code for the hidden character is 0x18

(found via Hex Fiend)

This character, along with others are part of a ' control character set'. The set also contains characters such as the tab (0x09) and newline (0x0A) - obviously those we don't want to remove.

In Objective-C, we can use the NSCharacterSet controlCharacterSet in conjunction with whitespaceAndNewlineCharacterSet to get just the blank characters that have no rendered width.

NSMutableCharacterSet* zeroWidthCharacterSet = [[NSCharacterSet controlCharacterSet] mutableCopy];
[zeroWidthCharacterSet formIntersectionWithCharacterSet:[[NSCharacterSet whitespaceAndNewlineCharacterSet] invertedSet]];

Then we can simply use the good old split by character set method

string = [[string componentsSeparatedByCharactersInSet:zeroWidthCharacterSet] componentsJoinedByString:@""];

Note that if a special character that uses more than one UTF8 character to represent itself (like Emoji) uses 0x18 then stripping it will break the character combo

Because the control characters are special, I don't believe you'd ever find them in an Emoji sequence.