Resizing a char[x] to char[y] at runtime

Question

OK, I hope I explain this one correctly. I have a struct:

typedef struct _MyData
{
   char Data[256];
   int  Index;
} MyData;

Now, I run into

Answer 1

I find KIV's trick quite usable. Though, I would suggest investigating the pointer issue first.

If you look at the malloc implementations
(check this IBM article, Listing 5: Pseudo-code for the main allocator),
When you allocate, the memory manager allocates a control header and
then free space following it based on your requested size.
This is very much like saying,

typedef struct _MyData
{
   int  size;
   char Data[1]; // we are going to break the array-bound up-to size length
} MyData;

---

Now, your problem is,
How do you pass such a (mis-sized?) structure to this other process?

That brings us the the question,
How does the other process figure out the size of this data?
I would expect a length field as part of the communication.

If you have all that, whats wrong with passing a pointer to the other process?
Will the other process identify the difference between a pointer to a structure and that to a allocated memory?