NSString* str = @"1二3四5";
NSLog(@"%c",[str characterAtIndex:0]);
NSLog(@"%c",[str characterAtIndex:1]);
NSString - characterAtIndex works well on ASCII chars, but how could I get the UTF8 character at the index of 2?
-- updated --
It seems unichar(16bits) can't represent all the UTF8 encoding strings(8bites to 32bites), so are there any method to get the char from NSString?
Unfortunately Dave's answer doesn't actually do what you want. The index supplied to rangeOfComposedCharacterSequenceAtIndex is an index of a UTF-16 code unit, 1 or 2 or which make a UTF-16 code point. So 1 is not the second UTF-16 code point if the first code point in the string requires 2 code units... (rangeOfComposedCharacterSequenceAtIndex returns the range of the code point which includes the code unit at the given index, so if your first char requires 2 code units then passing an index of 0 or 1 returns the same range).
If you want to find the UTF-8 sequence for a character you can use UTF8String and then parse the resultant bytes to find the byte sequence for the nth character. Or you can likewise use rangeOfComposedCharacterSequenceAtIndex starting at index 0 and iterate till you get to the nth character, then convert the 1 or 2 UTF-16 code units to UTF-8 code units.
I hope we're all missing something and this is built-in...
A start (needs bounds checking!) of a category which might help:
@interface NSString (UTF)
- (NSRange) rangeOfUTFCodePoint:(NSUInteger)number;
@end
@implementation NSString (UTF)
- (NSRange) rangeOfUTFCodePoint:(NSUInteger)number
{
NSUInteger codeUnit = 0;
NSRange result;
for(NSUInteger ix = 0; ix <= number; ix++)
{
result = [self rangeOfComposedCharacterSequenceAtIndex:codeUnit];
codeUnit += result.length;
}
return result;
}
@end
but this sort of stuff is more efficient using char * rather then NSString
You'd use the more verbose methods:
NSRange rangeOfSecondCharacter = [str rangeOfComposedCharacterSequenceAtIndex:1];
NSString *secondCharacter = [str substringWithRange:rangeOfSecondCharacter];
...with proper bounds and range checking, of course. Note that this gives you an NSString, an object, not a unichar or some other primitive data type.
Why don't you try to use something like that:
const char *yourWantedCharacter = [[yourSourceString substringWithRange:yourRange] UTF8String];
where yourSourceString is your NSString object, yourRange is an NSRange object with the index of the needed character as the location parameter and an length parameter of '0' (zero).
