byteArray to Hex NSString - adds some wrong hex content - ios

Question

I am trying to convert the byteArray to a Hex NSString.
Here is the solution that I referred to convert it into hex NSString. But, I discovered It add's ffffffffffffff. How can I get correct hex NSString?
Best way to serialize an NSData into a hexadeximal string
const char myByteArray[] = {
0x12,0x23,0x34,0x45,0x56,0x67,0x78,0x89,
0x12,0x23,0x34,0x45,
0x56,0x67,0x78,0x89 };
NSData *myByteData=[NSData dataWithBytes:myByteArray length:sizeof(myByteArray)];
NSMutableString *myHexString= [NSMutableString stringWithCapacity:myByteData.length*2];
for(int i=0;i<myByteData.length;i++){
;
NSString *resultString =[NSString stringWithFormat:#"%02lx",(unsigned long)myByteArray[i]];
[myHexString appendString:resultString];
}
The output String
12233445566778ffffffffffffff8912233445566778ffffffffffffff89

Answer 1

Don't use unsigned long for each of your bytes. And what's the point of myByteData if you don't use it?
And since you are not really using char, use uint8_t.
Try this:
const uint8_t myByteArray[] = {
0x12,0x23,0x34,0x45,0x56,0x67,0x78,0x89,
0x12,0x23,0x34,0x45,
0x56,0x67,0x78,0x89 };
size_t len = sizeof(myByteArray) / sizeof(uint8_t);
NSMutableString *myHexString = [NSMutableString stringWithCapacity:len * 2];
for (size_t i = 0; i < len; i++) {
[myHexString appendFormat:#"%02x", (int)myByteArray[i]];
}

Answer 2

Your initial byte data is char rather than unsigned char. This means that any values >127 (0x7f) will be seen as a twos-complement negative number, giving ffffffffffffff89.
If you change your data to be unsigned char you will get the desired result.
const unsigned char myByteArray[] = {
0x12,0x23,0x34,0x45,0x56,0x67,0x78,0x89,
0x12,0x23,0x34,0x45,
0x56,0x67,0x78,0x89 };
NSData *myByteData=[NSData dataWithBytes:myByteArray length:sizeof(myByteArray)];
NSMutableString *myHexString= [NSMutableString stringWithCapacity:myByteData.length*2];
for(int i=0;i<myByteData.length;i++){
NSString *resultString =[NSString stringWithFormat:#"%02lx",(unsigned long)myByteArray[i]];
[myHexString appendString:resultString];
}