NSString反轉字串

//文字反轉
-(NSString *)stringByReversed:(NSString*)sourceString{
    NSUInteger i = 0;
    NSUInteger j = sourceString.length - 1;
    unichar characters[sourceString.length];
    while (i < j) {
        characters[j] = [sourceString characterAtIndex:i];
        characters[i] = [sourceString characterAtIndex:j];
        i ++;
        j --;
    }
    if(i == j)
        characters[i] = [sourceString characterAtIndex:i];

    //從c array中，把字元一個一個寫出來
    return [NSString stringWithCharacters:characters length:sourceString.length];
} 

//利用文字反轉來取得網址中的檔案名稱
    NSString* tempString = [self stringByReversed:strURL];
    NSRange search = [tempString rangeOfString:@"/"];
    NSLog(@"%i", search.location);
    NSString* fileName =[self stringByReversed:[tempString substringToIndex:search.location]];
    NSLog(@"%@",fileName);