Question

my problem is that having this code:

int size=4384;
char buffer[size];
codifyDHCPmessage(buffer, message, size);

where message is an struct which only contains char[], and the function return in buffer, all the fields from the struct.

I test it going through the buffer array, and checking that all the fields are ok.

But my problem is that if i pass again that buffer into a new function as:

decodifyDHCPmessage(buffer,messageAux, size);

the first thing I do in that function is to check the size of buffer, which only tells me that is 4, when it’s suppossed to be 4384…. and I don’t know why.

I have to tell that I’m not an expert in C, and the pointer, and memory allocation issues are hard for me.

Thanks a lot in advance.

Answer 1

I suspect that your function signature looks like this:

void codifyDHCPmessage(char[], message_t, size_t);

(or similar)

The problem is that [] in a function signature really means *, that is, char[] is really char*. In other words, the array argument decays to a pointer whose size is, unsurprisingly, 4.

As far as I know (but I could be wrong …), C doesn’t allow you to pass arrays into functions at all, it just supports pointers. That’s why you need to pass the size as an explicit separate argument.