Objective c doesn't like my unichars?

Question

Xcode complaints about "multi-character character contant"'s when I try to do the following:

static unichar accent characters[] = { 'ā', 'á', 'ă', 'à' };

How do you make an array of characters, when not all of them are ascii? The following works just fine

static unichar accent[] = { 'a', 'b', 'c' }; 

Workaround

The closest work around I have found is to convert the special characters into hex, ie this works:

static unichar accent characters[] = { 0x0100, 0x0101, 0x0102 };

Answer 1

It's not that Objective-C doesn't like it, it's that C doesn't. The constant 'c' is for char which has 1 byte, not unichar which has 2 bytes. (see the note below for a bit more detail.)

There's no perfectly supported way to represent a unichar constant. You can use

char* s="ü";

in a UTF-8-encoded source file to get the unicode C-string, or

NSString* s=@"ü";

in a UTF-8 encoded source file to get an NSString. (This was not possible before 10.5. It's OK for iPhone.)

NSString itself is conceptually encoding-neutral; but if you want, you can get the unicode character by using -characterAtIndex:.

Finally two comments:

• If you just want to remove accents from the string, you can just use the method like this, without writing the table yourself:

  -(NSString*)stringWithoutAccentsFromString:(NSString*)s
  {
      if (!s) return nil;
      NSMutableString *result = [NSMutableString stringWithString:s];
      CFStringFold((CFMutableStringRef)result, kCFCompareDiacriticInsensitive, NULL);
      return result;
  }
  

  See the document of CFStringFold.

• If you want unicode characters for localization/internationalization, you shouldn't embed the strings in the source code. Instead you should use Localizable.strings and NSLocalizedString. See here.

Note: For arcane historical reasons, 'a' is an int in C, see the discussions here. In C++, it's a char. But it doesn't change the fact that writing more than one byte inside '...' is implementation-defined and not recommended. For example, see ISO C Standard 6.4.4.10. However, it was common in classic Mac OS to write the four-letter code enclosed in single quotes, like 'APPL'. But that's another story...

Another complication is that accented letters are not always represented by 1 byte; it depends on the encoding. In UTF-8, it's not. In ISO-8859-1, it is. And unichar should be in UTF-16. Did you save your source code in UTF-16? I think the default of XCode is UTF-8. GCC might do some encoding conversion depending on the setup, too...

Answer 2

Or you can just do it like this:

static unichar accent characters[] = { L'ā', L'á', L'ă', L'à' };

L is a standard C keyword which says "I'm about to write a UNICODE character or character set".

Works fine for Objective-C too.

Note: The compiler may give you a strange warning about too many characters put inside a unichar, but you can safely ignore that warning. Xcode just doesn't deal with the unicode characters the right way, but the compiler parses them properly and the result is OK.

Answer 3

Depending on your circumstances, this may be a tidy way to do it:

NSCharacterSet* accents = 
    [NSCharacterSet characterSetWithCharactersInString:@"āáăà"];

And then, if you want to check if a given unichar is one of those accent characters:

if ([accents characterIsMember:someOtherUnichar])
{
}

NSString also has many methods of its own for handling NSCharacterSet objects.