Access bit by union

st_union.c

typedef union {
    struct {
        uint8_t bit_0: 1;
        uint8_t bit_1: 1;
        uint8_t bit_2: 1;
        uint8_t bit_3: 1;
        uint8_t bit_4: 1;
        uint8_t bit_5: 1;
        uint8_t bit_6: 1;
        uint8_t bit_7: 1;
    };
    uint8_t byte_0;
}st_data;