I need to find a way to convert an arbitrary character typed by a user into an ASCII representation to be sent to a network service. My current approach is to create a lookup dictionary and send the corresponding code. After creating this dictionary, I see that it is hard to maintain and determine if it is complete:
__asciiKeycodes[#"F1"] = #(112);
__asciiKeycodes[#"F2"] = #(113);
__asciiKeycodes[#"F3"] = #(114);
//...
__asciiKeycodes[#"a"] = #(97);
__asciiKeycodes[#"b"] = #(98);
__asciiKeycodes[#"c"] = #(99);
Is there a better way to get ASCII character code from an arbitrary key typed by a user (using standard 104 keyboard)?
Objective C has base C primitive data types. There is a little trick you can do. You want to set the keyStroke to a char, and then cast it as an int. The default conversion in c from a char to an int is that char's ascii value. Here's a quick example.
char character= 'a';
NSLog("a = %ld", (int)test);
console output = a = 97
To go the other way around, cast an int as a char;
int asciiValue= (int)97;
NSLog("97 = %c", (char)asciiValue);
console output = 97 = a
Alternatively, you can do a direct conversion within initialization of your int or char and store it in a variable.
char asciiToCharOf97 = (char)97; //Stores 'a' in asciiToCharOf97
int charToAsciiOfA = (int)'a'; //Stores 97 in charToAsciiOfA
This seems to work for most keyboard keys, not sure about function keys and return key.
NSString* input = #"abcdefghijklkmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!##$%^&*()_+[]\{}|;':\"\\,./<>?~ ";
for(int i = 0; i<input.length; i ++)
{
NSLog(#"Found (at %i): %i",i , [input characterAtIndex:i]);
}
Use stringWithFormat call and pass the int values.
Related
I have a set of legacy data that that include individual Unicode chars formed based on struct:
struct LocalGrRec{
wchar_t cBegin;
int x2;
wchar_t cEnd;
in x2;
};
and a typical record looks like this, i.e., includes both long and short Unicode characters
{L'a', 0, L'¥', 3}
I can change the struct to make it easier to handle reading these characters into character variables:
wchar_t c = rec.cBegin;
// or
UTF32Char c = rec.cBegin;
Which one (or perhaps another choice that I don't know of) would make it easier to handle it. Please note that I need to process them as individual chars, but eventually I'll need to include them in an NSString.
What solution gives me the maximum flexibility and minimum pain?
And how would I read that character into a NSString?
Thanks
edit:
I need to compose NSString with it, not the other way around.
With unichar, here's the problem:
unichar c = L'•';
NSLog(#"%c", c); // produces: (") wrong character, presumably the first half of '•'
NSLog(#"%C", c); // produces: (\342\200)
I think you are looking for this method:
[NSString stringWithCharacters:(const unichar*) length:(NSUInteger)];
Just pass it an array of unichars and a length, and it will give you a NSString back
unichar list[3] = {'A', 'B', 'C'};
NSString *listString = [NSString stringWithCharacters:list length:3];
NSLog(#"listString: %#", listString);
I write a C function to read characters in an user-input string. Because this string is user-input, so it can contains any unicode characters. There's an Objective C method receives the user-input NSString, then convert this string to NSData and pass this data to the C function for processing. The C function searches for these symbol characters: *, [, ], _, it doesn't care any other characters. Everytime it found one of the symbols, it processes and then calls an Objective C method, pass the location of the symbol.
C code:
typedef void (* callback)(void *context, size_t location);
void process(const uint8_t *data, size_t length, callback cb, void *context)
{
size_t i = 0;
while (i < length)
{
if (data[i] == '*' || data[i] == '[' || data[i] == ']' || data[i] == '_')
{
int valid = 0;
//do something, set valid = 1
if (valid)
cb(context, i);
}
i++;
}
}
Objective C code:
//a C function declared in .m file
void mycallback(void *context, size_t location)
{
[(__bridge id)context processSymbolAtLocation:location];
}
- (void)processSymbolAtLocation:(NSInteger)location
{
NSString *result = [self.string substringWithRange:NSMakeRange(location, 1)];
NSLog(#"%#", result);
}
- (void)processUserInput:(NSString*)string
{
self.string = string;
//convert string to data
NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
//pass data to C function
process(data.bytes, data.length, mycallback, (__bridge void *)(self));
}
The code works fine if the input string contains only English characters. If it contains composed character sequences, multibyte characters or other unicode characters, the result string in processSymbolAtLocation method is not the expected symbol.
How to convert the NSString object to NSData correctly? How to get the correct location?
Thanks!
Your problem is that you start off with a UTF-16 encoded NSString and produce a sequence of UTF-8 encoded bytes. The number of code units required to represent a string in UTF-16 may not be equal to that number required to represent it in UTF-8, so the offsets in your two forms may not match - as you have found out.
Why are you using C to scan the string for matches in the first place? You might want to look at NSString's rangeOfCharacterFromSet:options:range: method which you can use to find the next occurrence of character from your set.
If you need to use C then convert your string into a sequence of UTF-16 words and use uint16_t on the C side.
HTH
I'm using the following code to obfuscate a passcode for a test app of mine.
- (NSString *)obfuscate:(NSString *)string withKey:(NSString *)key
{
// Create data object from the string
NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
// Get pointer to data to obfuscate
char *dataPtr = (char *) [data bytes];
// Get pointer to key data
char *keyData = (char *) [[key dataUsingEncoding:NSUTF8StringEncoding] bytes];
// Points to each char in sequence in the key
char *keyPtr = keyData;
int keyIndex = 0;
// For each character in data, xor with current value in key
for (int x = 0; x < [data length]; x++)
{
// Replace current character in data with
// current character xor'd with current key value.
// Bump each pointer to the next character
*dataPtr = *dataPtr++ ^ *keyPtr++;
// If at end of key data, reset count and
// set key pointer back to start of key value
if (++keyIndex == [key length])
keyIndex = 0, keyPtr = keyData;
}
return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
}
This works like a charm with all strings, but i've ran into a bit of a problem comparing the following results
NSLog([[self obfuscate:#"0000", #"maki"]); //Returns 0]<W
NSLog([[self obfuscate:#"0809", #"maki"]); //Returns 0]<W
As you can see, the two strings with numbers in, while different, return the same result! Whats gone wrong in the code i've attached to result in the same result for these two numbers?
Another example:
NSLog([self obfuscate:#"8000" withKey:#"maki"]); //Returns 8U4_
NSLog([self obfuscate:#"8290" withKey:#"maki"]); //Returns 8U4_ as well
I may be misunderstanding the concept of obfuscation, but I was under the impression that each unique string returns a unique obfuscated string!
Please help me fix this bug/glitch
Source of Code: http://iosdevelopertips.com/cocoa/obfuscation-encryption-of-string-nsstring.html
The problem is your last line. You create the new string with the original, unmodified data object.
You need to create a new NSData object from the modified dataPtr bytes.
NSData *newData = [NSData dataWithBytes:dataPtr length:data.length];
return [[NSString alloc] initWithData:newData encoding:NSUTF8StringEncoding];
But you have some bigger issues.
The calls to bytes returns a constant, read-only reference to the bytes in the NSData object. You should NOT be modifying that data.
The result of your XOR on the character data could, in theory, result in a byte stream that is no longer a valid UTF-8 encoded string.
The obfuscation algorithm that you have selected is based on XORing the data and the "key" values together. Generally, this is not very strong. Moreover, since XOR is symmetric, the results are very prone to producing duplicates.
Although your implementation is currently broken, fixing it would not be of much help in preventing the algorithm from producing identical results for different data: it is relatively straightforward to construct key/data pairs that produce the same obfuscated string - for example,
[self obfuscate:#"0123" withKey:#"vwxy"]
[self obfuscate:#"pqrs" withKey:#"6789"]
will produce identical results "FFJJ", even though both the strings and the keys look sufficiently different.
If you would like to "obfuscate" your strings in a cryptographically strong way, use a salted secure hash algorithm: it will produce very different results for even slightly different strings.
I'm experiencing a very odd issue with atoi(char *). I'm trying to convert a char into it's numerical representation (I know that it is a number), which works perfectly fine 98.04% of the time, but it will give me a random value the other 1.96% of the time.
Here is the code I am using to test it:
int increment = 0, repetitions = 10000000;
for(int i = 0; i < repetitions; i++)
{
char randomNumber = (char)rand()%10 + 48;
int firstAtoi = atoi(&randomNumber);
int secondAtoi = atoi(&randomNumber);
if(firstAtoi != secondAtoi)NSLog(#"First: %d - Second: %d", firstAtoi, secondAtoi);
if(firstAtoi > 9 || firstAtoi < 0)
{
increment++;
NSLog(#"First Atoi: %d", firstAtoi);
}
}
NSLog(#"Ratio Percentage: %.2f", 100.0f * (float)increment/(float)repetitions);
I'm using the GNU99 C Language Dialect in XCode 4.6.1. The first if (for when the first number does not equal the second) never logs, so the two atoi's return the same result every time, however, the results are different every time. The "incorrect results" seemingly range from -1000 up to 10000. I haven't seen any above 9999 or any below -999.
Please let me know what I am doing wrong.
EDIT:
I have now changed the character design to:
char numberChar = (char)rand()%10 + 48;
char randomNumber[2];
randomNumber[0] = numberChar;
randomNumber[1] = 0;
However, I am using:
MAX(MIN((int)(myCharacter - '0'), 9), 0)
to get the integer value.
I really appreciate all of the answers!
atoi expects a string. You have not given it a string, you have given it a single char. A string is defined as some number of characters ended by the null character. You are invoking UB.
From the docs:
If str does not point to a valid C-string, or if the converted value would be out of the range of values representable by an int, it causes undefined behavior.
Want to "convert" a character to its integral representation? Don't overcomplicate things;
int x = some_char;
A char is an integer already, not a string. Don't think of a single char as text.
If I'm not mistaken, atoi expects a null-terminated string (see the documentation here).
You're passing in a single stack-based value, which does not have to be null-terminated. I'm extremely surprised it's even getting it right: it could be reading off hundreds of garbage numbers into eternity, if it never finds a null-terminator. If you just want to get the number of a single char (as in, the numeric value of the char's human-readable representation), why don't you just do int numeric = randomNumber - 48 ?
I have a binary file I've loaded using an NSData object. Is there a way to locate a sequence of characters, 'abcd' for example, within that binary data and return the offset without converting the entire file to a string? Seems like it should be a simple answer, but I'm not sure how to do it. Any ideas?
I'm doing this on iOS 3 so I don't have -rangeOfData:options:range: available.
I'm going to award this one to Sixteen Otto for suggesting strstr. I went and found the source code for the C function strstr and rewrote it to work on a fixed length Byte array--which incidentally is different from a char array as it is not null terminated. Here is the code I ended up with:
- (Byte*)offsetOfBytes:(Byte*)bytes inBuffer:(const Byte*)buffer ofLength:(int)len;
{
Byte *cp = bytes;
Byte *s1, *s2;
if ( !*buffer )
return bytes;
int i = 0;
for (i=0; i < len; ++i)
{
s1 = cp;
s2 = (Byte*)buffer;
while ( *s1 && *s2 && !(*s1-*s2) )
s1++, s2++;
if (!*s2)
return cp;
cp++;
}
return NULL;
}
This returns a pointer to the first occurrence of bytes, the thing I'm looking for, in buffer, the byte array that should contain bytes.
I call it like this:
// data is the NSData object
const Byte *bytes = [data bytes];
Byte* index = [self offsetOfBytes:tag inBuffer:bytes ofLength:[data length]];
Convert your substring to an NSData object, and search for those bytes in the larger NSData using rangeOfData:options:range:. Make sure that the string encodings match!
On iPhone, where that isn't available, you may have to do this yourself. The C function strstr() will give you a pointer to the first occurrence of a pattern within the buffer (as long as neither contain nulls!), but not the index. Here's a function that should do the job (but no promises, since I haven't tried actually running it...):
- (NSUInteger)indexOfData:(NSData*)needle inData:(NSData*)haystack
{
const void* needleBytes = [needle bytes];
const void* haystackBytes = [haystack bytes];
// walk the length of the buffer, looking for a byte that matches the start
// of the pattern; we can skip (|needle|-1) bytes at the end, since we can't
// have a match that's shorter than needle itself
for (NSUInteger i=0; i < [haystack length]-[needle length]+1; i++)
{
// walk needle's bytes while they still match the bytes of haystack
// starting at i; if we walk off the end of needle, we found a match
NSUInteger j=0;
while (j < [needle length] && needleBytes[j] == haystackBytes[i+j])
{
j++;
}
if (j == [needle length])
{
return i;
}
}
return NSNotFound;
}
This runs in something like O(nm), where n is the buffer length, and m is the size of the substring. It's written to work with NSData for two reasons: 1) that's what you seem to have in hand, and 2) those objects already encapsulate both the actual bytes, and the length of the buffer.
If you're using Snow Leopard, a convenient way is the new -rangeOfData:options:range: method in NSData that returns the range of the first occurrence of a piece of data. Otherwise, you can access the NSData's contents yourself using its -bytes method to perform your own search.
I had the same problem.
I solved it doing the other way round, compared to the suggestions.
first, I reformat the data (assume your NSData is stored in var rawFile) with:
NSString *ascii = [[NSString alloc] initWithData:rawFile encoding:NSAsciiStringEncoding];
Now, you can easily do string searches like 'abcd' or whatever you want using the NSScanner class and passing the ascii string to the scanner. Maybe this is not really efficient, but it works until the -rangeOfData method will be available for iPhone also.