uint8_t to bit-field in C

main.c

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

typedef union {
    uint8_t value;
    struct {
        unsigned flag0:1;
        unsigned flag1:1;
        unsigned flag2:1;
        unsigned flag3:1;
        unsigned flag4:1;
        unsigned flag5:1;
        unsigned flag6:1;
        unsigned flag7:1;
    } flags;
} Register;

int main() {
    Register my_reg;
    my_reg.value = 0b00000001;
    
    if (reg.flags.flag0) {
        printf("Flag 0 = true\n");
    } else {
        printf("Flag 0 = false\n");
    }

    return 0;
}

Handy approach when you want to give more structure to registers. Especially when dealing with registers read from I2C or SPI devices.
Initialize the Register union by its value and query the flags struct after that. The value is eg. the raw byte you get from the I2C device.
Define Register unions for each register type you want to deal with and rename the flags to something meaningful.