How to use structure with dynamically changing size of data?

Question

Question for C only, C++ and vectors do not solve problem.

I have such structure:

typedef __packed struct Packet_s
{
  U8  head;
  U16 len;
  U32 id;
  U         


        

Answer 1

Is it possible to use my structure if field "DATA" is longer than 1 byte?

No, since it has only room for 1 data byte. But you can use a slightly modified version of your structure.

typedef __packed struct Packet_s
{
  U8  head;
  U16 len;
  U32 id;
  U8  data[DATALENMAX]; // define appropriately
  U8  end;
  U16 crc;
} Packet_t, *Packet_p;

Of course, you'd have to adapt the copying accordingly:

memcpy(&Packet, &Buffer, buffer_len), memmove(&Packet.end, &Packet.data[buffer_len-7-3], 3);

Regarding the added problems, it's necessary to pass the data length to SendResponce():

SendResponce(rspData, sizeof rspData);

void SendResponce(uint8_t* data_rsp, int datalen)
{
  Packet_t ResponceData;
  uint16_t crc;
  uint8_t *data;

  ResponceData.head  = 0x24;
  ResponceData.len   = 7+datalen+3; // HERE WAS PROBLEM ONE
  ResponceData.id   = SPECIAL_ID_X;
  memcpy(ResponceData.data, data_rsp, datalen); // HERE WAS PROBLEM TWO
  ResponceData.data[datalen] = 0x0D; // symbol '\r'
  data = (uint8_t*)&ResponceData;
  crc = GetCrc(data, 7+datalen+1); // last 2 bytes with crc
  ResponceData.crc = crc;//(ack_crc >> 8 | ack_crc);
  memmove(ResponceData.data+datalen+1, &ResponceData.crc, 2);
  SendData((U8*)&ResponceData, ResponceData.len);  // Send rsp packet
}