Print bytes in binary C

print_bin.c

#include <stdio.h>
#include <inttypes.h>

/* Credit to https://stackoverflow.com/questions/111928/is-there-a-printf-converter-to-print-in-binary-format */

#define BYTE_TO_BIN_FORMAT "%c%c%c%c%c%c%c%c"
#define BYTE_TO_BIN(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') 

#define LITTLE_ENDIAN 0
#define BIG_ENDIAN    1

void print_bin(const void *data, const size_t size, const uint8_t endianness) {

    printf("data: 0b");

    const uint8_t *bytes = (const uint8_t *)data;

    for (size_t i = 0, idx = i; i < size; i++ ) {

        if (endianness == BIG_ENDIAN) {
            /* Reverse byte order */
            idx = size - i - 1;
        } else {
            idx = i;
        }

        printf(BYTE_TO_BIN_FORMAT, BYTE_TO_BIN(bytes[idx]));

        if (i < size - 1) {
            /* Seperate each byte when printing */
            printf(" ");
        }

    }

    printf("\n");

}

int main(void) {

    /* 0xAA = 0b10101010 */
    uint32_t a = 0x00AA00AA;

    printf("[Little endian] ");
    print_bin(&a, sizeof(uint32_t), LITTLE_ENDIAN);

    printf("[Big endian] ");
    print_bin(&a, sizeof(uint32_t), BIG_ENDIAN);

    return 0;
}