Question

I’m serializing structs into byte-streams. My method is simple:
pack all ints in little endian order and copy strings including the null terminator. The other side has to statically know how to unpack the byte-stream, there is no additional metadata.

My problem is, that I do not know how to handle the the NULL pointer?

I need to send something, because there is no additional metadata in the stream.

I considered the following two options:

1. Send a ‘\0’ and make the receiving side interpret it as NULL in any case

2. Send a ‘\0’ and make the receiving side interpret it as ‘\0’ in any case (alloc a byte)

3. Send a special character representing char* str == NULL, e.g. ETX, EOT, EM ?

What do you think?

Answer 1

It looks like you are currently trying to tell the receiving end that the end of the serialized string has been reached by passing it a special character. There are a million cases that can screw you over with this:

What if your struct contains a byte that is equal to that special character. Escape it with another special character. What if your struct contains a byte sequence that is equal to your escape character followed by your special character, check for that too?

Yeah it’s doable, but I think that’s not a very good solution and you’ll have to write a parser to look for the escape character and then anyone who takes a look at the code later will spend two hours trying to figure out what’s going on.

(tl;dr) Instead… just make the first 32 bits of the serialized string equal to the number of bytes in the string. This only costs 4 bytes per serialization, solves all your problems, you won’t have to write a parser or worry about special characters, and will make it a lot easier on the next guy who gets to read through your code!

edit

Thanks to JeremyP I’ve just realized that I didn’t really answer your question. Send one of these guys for every string:

struct s_str
{
bool is_null;
int size;
char* str;
};

If it’s null, simply set is_null to true and you don’t really have to worry about the other two.
If it’s size zero, set is_null to false and size to zero.
If str contains just a ‘\0’, set is_null to false, size to one, and str[0] to ‘\0’

In my opinion, this might not be the most memory efficient way (you could probably save a byte somewhere somehow) but is definitely quite clear in what you’re doing, and again the next guy that comes along will like this a lot more.