void endianTest_union()
{
    union     // sizeof(int) == 4
    {
        int i;
        unsigned char ch[4];
    } U;

    U.i = 0x12345678;        // writing to int i

    if(U.ch[0]==0x78 && U.ch[1]==0x56
            && U.ch[2]==0x34 && U.ch[3]==0x12)  // followed by
        puts("Little Endian");                  //reading from unsigned char: OK

    else if (U.ch[3]==0x78 && U.ch[2]==0x56
             && U.ch[1]==0x34 && U.ch[0]==0x12)
        puts("Big Endian");
    else
        puts("Middle Endian");
}

void endianTest_sans_union()
{
    int n = 0x12345678;     // sizeof(int) == 4
    unsigned char* p = (unsigned char*)&n;   // reinterpreting int
                                             // through unsigned char ptr: OK
    if(p[0]==0x78 && p[1]==0x56
       && p[2]==0x34 && p[3]==0x12)
        puts("Little Endian");

    else if (p[3]==0x78 && p[2]==0x56
       && p[1]==0x34 && p[0]==0x12)
        puts("Big Endian");

    else
        puts("Middle Endian");
}

void undef_beh()
{
    int n = 0x12345678;     // sizeof(int) == 4
    short int * p = (short int *)&n;   // reinterpreting int
                                       // through short int ptr: not OK
    printf("\nlower short int: %x\n",p[0]);  // breaks strict aliasing rule
    printf("higher short int: %x\n",p[1]);   // fortunately this produces warning (in gcc)
                                          // still prints p[0] == 0x5678; p[1] == 0x1234
}

void undef_beh_union()
{
    union     // sizeof(int) == 4
    {
        int i;
        short int p[2];
    } U;

    U.i = 0x12345678;        // writing to int i
    
    printf("\nlower short int: %x\n",U.p[0]);  // followed by
    printf("higher short int: %x\n",U.p[1]);   // reading from short int member : not OK
                                          // prints U.p[0] == 0x5678; U.p[1] == 0x1234
}

int main()
{
endianTest_union();
endianTest_sans_union();
undef_beh();
undef_beh_union();

return 0;
}

Little Endian
Little Endian

lower short int: 5678
higher short int: 1234

lower short int: 5678
higher short int: 1234