reading packed struct bits created by VehpuS - https://repl.it/@VehpuS/reading-packed-struct-bits

struct-packed-bits.c

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

typedef struct __attribute__((__packed__)) data_block_t {
    uint8_t  a;
    uint8_t  b : 1;
    uint8_t  c : 1;
    uint8_t  d : 1;
    uint8_t  e : 1;
    uint8_t  f : 1;
    uint8_t  g : 1;
    uint8_t  h : 1;
    uint8_t  i : 1;
    uint16_t j;
} data_block;

#define BYTE_TO_BINARY_PATTERN "%c%c%c%c%c%c%c%c"
#define BYTE_TO_BINARY(byte)   \
    (byte & 0x80 ? '1' : '0'), \
    (byte & 0x40 ? '1' : '0'), \
    (byte & 0x20 ? '1' : '0'), \
    (byte & 0x10 ? '1' : '0'), \
    (byte & 0x08 ? '1' : '0'), \
    (byte & 0x04 ? '1' : '0'), \
    (byte & 0x02 ? '1' : '0'), \
    (byte & 0x01 ? '1' : '0')

int main(void) {
  data_block data = {
    .a = 0,
    .b = 1,
    .d = 1,
    .j = 3,
  };
  printf(BYTE_TO_BINARY_PATTERN ":", BYTE_TO_BINARY(((uint8_t*) &data)[2]));
  printf(BYTE_TO_BINARY_PATTERN ":", BYTE_TO_BINARY(((uint8_t*) &data)[1]));
  printf(BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(((uint8_t*) &data)[0]));
  return 0;
}