Converting NSData that contains UTF-8 and null bytes to string - objective-c

Question

I have an __NSCFData object. I know what's inside it.
61 70 70 6c 65 2c 74 79 70 68 6f 6f 6e 00 41 52 4d 2c 76 38 00
I tried converting it to a string with initWithData: and stringWithUTF8String: and it gives me "apple,typhoon". The conversion is terminated at 00
The data actually is
61 a
70 p
70 p
6c l
65 e
2c ,
74 t
79 y
70 p
68 h
6f o
6f o
6e n
00 (null)
41 A
52 R
4d M
2c ,
76 v
38 8
00 (null)
How can I properly convert this without loss of information?

Answer 1

The documentation for stringWithUTF8String describes its first parameter as:
A NULL-terminated C array of bytes in UTF8 encoding.
Which is why your conversion stops at the first null byte.
What you appear to have is a collection of C strings packed into a single NSData. You can convert each one individually. Use the NSData methods bytes and length to obtain a pointer to the bytes/first C string and the total number of bytes respectively. The standard C function strlen() will give you the length in bytes of an individual string. Combine these and some simple pointer arithmetic and you can write a loop which converts each string and, for example, stores them all into an array or concatenates them.
If you get stuck implementing the solution ask a new question, show your code, and explain the issue. Someone will undoubtedly help you with the next step.
HTH

Answer 2

In contrast to the intention of some answers, the stored strings in instances of NSString are not 0-terminated. Even there might be problems with writing them out (since underlying C functions for output expects a 0-terminated string), the instances itself can contain a \0:
NSString *zeroIncluded = #"A\0B";
NSLog(#"%ld", [zeroIncluded length]);
// prints 3
To create such an instance you can use methods that have a bytes and a length parameter, i. e. -initWithBytes:length:encoding:. Therefore something like this should work:
NSData *data = …
[[NSString alloc] initWithBytes:[data bytes] length:[data length] encoding:NSUTF8StringEncoding];
However, as intended by CRD, you might check, whether you want to have such a string.

Answer 3

0, or null, is the sentinel value which terminates strings, so you're going to have to deal with it somehow if you want to automatically dump the bytes into a string. If you don't, the string, or things that try to print it, for example, will assume the end of string is reached when reaching the NULL.
Just replace the bytes as they occur with something printable, like a space. Use whatever value works for you.
Example:
// original data you have from somewhere
char something[] = "apple,typhoon\0ARM,v8\0";
NSData *data = [NSData dataWithBytes:something length:sizeof(something)];
// Find each null terminated string in the data
NSMutableArray *strings = [NSMutableArray new];
NSMutableString *temp = [NSMutableString string];
const char *bytes = [data bytes];
for (int i = 0; i < [data length]; i++) {
unsigned char byte = (unsigned char)bytes[i];
if (byte == 0) {
if ([temp length] > 0) {
[strings addObject:temp];
temp = [NSMutableString string];
}
} else {
[temp appendFormat:#"%c", byte];
}
}
// Results
NSLog(#"strings count: %lu", [strings count]);
[strings enumerateObjectsUsingBlock:^(NSString *string, NSUInteger idx, BOOL * _Nonnull stop) {
NSLog(#"%ld: %#", idx, string);
}];
// strings count: 2
// 0: apple,typhoon
// 1: ARM,v8