Bit manipulation through unions

#include <stdio.h>

typedef struct {
    unsigned b0: 8, b1: 8, b2: 8, b3: 8;
} word_bytes;

typedef struct{
    unsigned b0: 1, b1: 1, b2: 1, b3: 1, b4: 1, b5: 1, b6: 1, b7: 1, b8: 1, b9: 1, b10: 1, b11: 1, b12: 1, b13: 1, b14: 1, b: 15, b16: 1, b17: 1, b18: 1, b19: 1, b20: 1, b21: 1, b22: 1, b23: 1, b24: 1, b25: 1, b26: 1, b27: 1, b28: 1, b29: 1, b30: 1, b31: 1;
} word_bits;

typedef union {
    int         i;
    word_bits   bit;
    word_bytes  bytes;
} word;

int main()
{
    // sets all bits to 0
    word w = {0};

    // turing on bits
    w.bit.b8 = 1;
    w.bit.b12 = 1;

    // first 8 bits
    w.bytes.b0 = 'a';

    // third 8 bits
    w.bytes.b2 = 'A';

    // fourth 8 bits
    w.bytes.b3 = 12;

    printf("w.i = %d\n", w.i);
    printf("w.b2 = %d  %c\n", w.bytes.b2, w.bytes.b2);
    return 0;
}