70. Packet Layout Using Union with Struct

#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) {
    Packet packet;
    packet.fields.start     = s;
    packet.fields.command   = c;
    packet.fields.data      = d;
    packet.fields.crc       = crc;
    packet.fields.end       = e;

    // Set packet.raw field
    packet.raw[0] = packet.fields.start;
    packet.raw[1] = packet.fields.command;
    packet.raw[2] = packet.fields.data & 0xFF;
    packet.raw[3] = (packet.fields.data >> 8) & 0xFF;
    packet.raw[4] = packet.fields.crc;
    packet.raw[5] = packet.fields.end;
    
    // Print raw bytes:
    for (int i = 0; i < 6; i++) {
        printf("%d ", packet.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;
}