C: Recommended style for dynamically sized structs

Question

I need to transfer packets through the internet whose length should be dynamic.

struct packet
{
  int id;
  int filename_len;
  char filename[];
};
         


        

Answer 1

I suggest to use char filename[1] and include a terminating 0-byte. This way, you can malloc() the correct structure size and avoid one-off errors like this:

ptr = malloc(sizeof(struct packet)+filename_len);
strncpy(&ptr->filename, filename, filename_len);

But the receiver must to know that it needs to read filename_len+1 bytes.