An exam test question I found online, testing sub-addressing 64-bit long values and endianness.

address_test.c

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

int main() {
    uint64_t n[2] = {0xaabbccddeeff1122, 0x1122334455667788};
    for (int i = 0; i < 2; ++i) {
        printf("at address: %lx\t number: %lx\n", (size_t)&n[i], n[i]);
        for (int k = 0; k < 8; ++k) {
            uint8_t* c = ((uint8_t*)(&n[i])) + k;
            printf("at address: %lx\t number: %x\n", (size_t)c, *c);
        }
        printf("\n");
    }
}

// My guess:
// at address: <addr1>      number: 0xaabbccddeeff1122
// at address: <addr1>      number: 0xaa
// at address: <addr1>+8    number: 0xbb
// at address: <addr1>+16   number: 0xcc
// at address: <addr1>+24   number: 0xdd
// at address: <addr1>+32   number: 0xee
// at address: <addr1>+40   number: 0xff
// at address: <addr1>+48   number: 0x11
// at address: <addr1>+56   number: 0x22
// at address: <addr2>      number: 0x1122334455667788
// at address: <addr2>      number: 0x11
// at address: <addr2>+8    number: 0x22
// at address: <addr2>+16   number: 0x33
// at address: <addr2>+24   number: 0x44
// at address: <addr2>+32   number: 0x55
// at address: <addr2>+40   number: 0x66
// at address: <addr2>+48   number: 0x77
// at address: <addr2>+56   number: 0x88

// Actual
// at address: 7ffce6b4bae0         number: aabbccddeeff1122
// at address: 7ffce6b4bae0         number: 22
// at address: 7ffce6b4bae1         number: 11
// at address: 7ffce6b4bae2         number: ff
// at address: 7ffce6b4bae3         number: ee
// at address: 7ffce6b4bae4         number: dd
// at address: 7ffce6b4bae5         number: cc
// at address: 7ffce6b4bae6         number: bb
// at address: 7ffce6b4bae7         number: aa

// at address: 7ffce6b4bae8         number: 1122334455667788
// at address: 7ffce6b4bae8         number: 88
// at address: 7ffce6b4bae9         number: 77
// at address: 7ffce6b4baea         number: 66
// at address: 7ffce6b4baeb         number: 55
// at address: 7ffce6b4baec         number: 44
// at address: 7ffce6b4baed         number: 33
// at address: 7ffce6b4baee         number: 22
// at address: 7ffce6b4baef         number: 11

// Reason for difference: Endianness
// x86_64 is little endian so the lowest bytes come first