Packet Layout Using Union with Struct

Code

#include <stdio.h>
#include <stdint.h>

typedef union {
    struct {
        uint8_t start;
        uint8_t command;
        uint16_t data;
        uint8_t crc;
        uint8_t end;
    } fields;
    uint8_t raw[6];
} Packet;

// Fill struct fields and print raw bytes
void build_and_print_packet(uint8_t s, uint8_t c, uint16_t d, uint8_t crc, uint8_t e) {
    // Your logic here
    Packet p;

    p.fields.start   = s;
    p.fields.command = c;
    p.fields.data    = d;
    p.fields.crc     = crc;
    p.fields.end     = e;

    for(int i = 0; i < 6; i++){
        printf("%u ", p.raw[i]);
    }
}

int main() {
    uint8_t s, c, crc, e;
    uint16_t d;
    scanf("%hhu %hhu %hu %hhu %hhu", &s, &c, &d, &crc, &e);
    build_and_print_packet(s, c, d, crc, e);
    return 0;
}

Solving Approach

• uint16_t data splits into two bytes inside the union.
• On little-endian systems:
  • low byte → raw[2]
  • high byte → raw[3]
• For data = 255, high byte is 0.

• Therefore, raw output becomes:

  170 255 255 0 254 85