Struct to string and vice versa

Question

I would like to take the memory generated from my struct and push it into a byte array (char array) as well as the other way around (push the byte array back into a struct). It would be even better if I could skip the string generation step and go directly to writing memory into the EEPROM. (Do not worry about the eeprom bit, I can handle that by reading & writing individual bytes)

// These are just example structs (I will be using B)
typedef struct {int a,b,c;} A;
typedef struct {A q,w,e;} B;

#define OFFSET 0 // For now

void write(B input)
{
  for (int i=0;i<sizeof(B);i++)
  {
    eepromWrite(i+OFFSET,memof(input,i));
  }
}

B read()
{
  B temp;
  for (int i=0;i<sizeof(B);i++)
  {
    setmemof(temp,i,eepromRead(i+OFFSET));
  }
  return temp;
}

This example I wrote is not supposed to compile, it was meant to explain my ideas in a platform independent environment.

PLEASE NOTE: memof and setmemof do not exist. This is what I am asking for though my question. An alternative answer would be to use a char array as an intermediate step.

It's hard to understand what you're asking for here, can you please clarify your question? — Mahmoud Al-Qudsi, Apr 01 '12 at 22:52
How do you want your [structures packed](http://tuxsudh.blogspot.com/2005/05/structure-packing-in-gcc.html)? — sarnold, Apr 01 '12 at 22:58
Your question is unclear. Are you looking to make this work in a platform independent manner? If so you need a serialization & de-serialization mechanism. — Amardeep AC9MF, Apr 01 '12 at 23:00
@MahmoudAl-Qudsi I am trying to break out the memory allocated from a stuct into bytes (via one byte at a time). Then loop though those bytes to dump the struct into EEPROM. — jakebird451, Apr 01 '12 at 23:01
So just replace `setmemof` with `eepromWrite`.... What am I missing here? — Mahmoud Al-Qudsi, Apr 01 '12 at 23:02
@MahmoudAl-Qudsi eepromWrite only takes in a byte, not a struct. — jakebird451, Apr 01 '12 at 23:12
Yes... so you use `unsigned char i` instead of `int i` as you loop over your data. `++i` isn't going to move to the next struct, it's going to move to the next byte (depending on your declaration). — Mahmoud Al-Qudsi, Apr 01 '12 at 23:14
@MahmoudAl-Qudsi changing `int` to `unsigned char i` would break the program. The struct size is larger than 255 (in my project). I need the functions `memof` and `setmemof`. Right now it is just implemented as sudo code. — jakebird451, Apr 01 '12 at 23:22

score 1 · Accepted Answer · edited May 23 '17 at 11:59

Assuming your structures contain objects and not pointers, you can do this with a simple cast:

save_b(B b) {
  unsigned char b_data[sizeof(B)];
  memcpy(b_data, (unsigned char *) &b, sizeof(B));
  save_bytes(b_data, sizeof(B));
}

Actually, you shouldn't need to copy from the structure into a char array. I was just hoping to make the idea clear.

Be sure to look into #pragma pack, with determines how the elements in the stuctures are aligned. Any alignment greater than one byte may increase the size unnecessarily.

Struct to string and vice versa

1 Answers1