#include <stdio.h>
#include <stdint.h>
int main() 
{
    union {
        uint32_t u32;
        uint8_t  u8[4];
    } demo;
    
    demo.u32 = 0x12345678;
    /*
     * using the address, it depends on the byte ordering, what comes out.
     */
    printf("lowest address:  u8[0] = %hhx \n", demo.u8[0]);
    printf("highest address: u8[3] = %hhx \n", demo.u8[3]);
    /*
     * using math operations, the least significant byte can be masked or calculated
     * independently from the byte ordering.
     */
    printf("least significant byte:  %hhx \n", demo.u32 % 256);              // modulo 
    printf("least significant byte:  %hhx \n", demo.u32 & 0xff);             // bitwise AND
    printf("most significant byte:   %hhx \n", demo.u32 / (256 * 256 * 256)); // division
    printf("most significant byte:   %hhx \n", demo.u32 >> 24);               // bit shift

    if (demo.u8[0] == demo.u32 % 256) {
        printf(" -> little endian\n");
    } else {
        printf(" -> big endian\n");
    }

    return 0;
}