How to convert from NSString to const char* with umlauts in Objective-C?

Question

I have a problem with umlauts in a NSString converting to const char*.

This method parses a textfile of words (line by line), saves the words as strings in NSArray *results. Then convert to const char tmpConstChars. This const char saves, for example, an 'ä' like '√§'. How to convert from NSString to const char * - I Thought this is correct.

- (void)inputWordsByFile:(NSString *)path
{

    NSError *error = [[NSError alloc] init];
    NSString *content = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&error];
    NSArray *results = [content componentsSeparatedByString:@"\n"];

    NSMutableArray *words = [[NSMutableArray alloc] initWithArray:results];
    [words removeLastObject];
    for(int i=0; i<[words count]; i++){

    const char *tmpConstChars = [[words objectAtIndex:i] UTF8String];
    [self addWordToTree:tmpConstChars];

    }
}

The problem could be with how you are viewing the text... are you sure you're viewing the text in something that is UTF8 aware, or something that is configured to interpret UTF8 encoded text? — dreamlax
– dreamlax, Commented Jun 17, 2011 at 11:13
NSLog(@"%s",tmpConstChars+2);will give me "§hlen" for "zählen", it should give me "hlen". — malteriechmann
– malteriechmann, Commented Jun 17, 2011 at 11:22

zoul · Accepted Answer · 2011-06-21 06:45:36Z

2

Unless I am mistaken, the UTF8String method returns the UTF-8 encoding bytes for the string. For zählen, these are:

$ perl -MEncode -Mutf8 -E 'say join ", ", map ord, split //, encode("utf8", "zählen")'
122, 195, 164, 104, 108, 101, 110

…where <195, 164> is the UTF-8 encoding sequence for ä. Thus, when you poke into tmpChars+2, you get the character with ASCII code 164 back. Which is probably not what you want. Aren’t you more after unichars? There’s a characterAtIndex: method that returns those, albeit one after one:

NSString *test = @"zählen";
unichar c = [test characterAtIndex:1];
NSLog(@"---> %C", c); // ---> ä

edited Jun 21, 2011 at 6:45

answered Jun 17, 2011 at 11:58

zoul

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3 Comments

malteriechmann Over a year ago

unichar tmpConstChars = [[words objectAtIndex:i] characterAtIndex:0];

zoul Over a year ago

You’ve got to be doing something wrong, it works for me. I’ll update the answer with sample code.

Rob Napier Over a year ago

@malteriechmann, what are you doing with tmpConstChars to get your mistaken character? Remember, unichar are 2-bytes long, so you can't read tmpConstChars[2] and get ä. %C is the correct format code for unichar. If you're expecting ä to be 224, then you need to decode using NSISOLatin1StringEncoding. But then you'll be limited to the Latin1 code page.

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