BIG / LITTLE ENDIANESS - Interpreting Data

Now let's do an example with multi-byte data (finally!). Quick review: a "short int" is a 2-byte (16-bit) number, which can range from 0 - 65535 (if unsigned). Let's use it in an example:
short *s; // pointer to a short int (2 bytes)
s = 0; // point to location 0; *s is the value
So, s is a pointer to a short, and is now looking at byte location 0 (which has W). What happens when we read the value at s?
* Big endian machine: I think a short is two bytes, so I'll read them off: location s is address 0 (W, or 0x12) and locaiton s + 1 is address 1 (X, or 0x34). Since the first byte is biggest (I'm big-endian!), the number must be 256 * byte 0 + byte 1, or 256*W + X, or 0x1234. I multiplied the first byte by 256 (2^8) because I needed to shift it over 8 bits.
* Little endian machine: I don't know what Mr. Big Endian is smoking. Yeah, I agree a short is 2 bytes, and I'll read them off just like him: location s is 0x12, and location s + 1 is 0x34. But in my world, the first byte is the littlest! The value of the short is byte 0 + 256 * byte 1, or 256*X + W, or 0x3412.

Keep in mind that both machines start from location s and read memory going upwards. There is no confusion about what location 0 and location 1 mean. There is no confusion that a short is 2 bytes.But do you see the problem? The big-endian machine thinks s = 0x1234 and the little-endian machine thinks s = 0x3412. The same exact data gives two different numbers. Probably not a good thing.
Test - BIG / LITTLE Endianness of your system ...
FindLittleOrBig()
{
int i = 0x12345678;
if ( *(char *)&i == 0x12 )
printf(“Big endian\n”);
else if ( *(char *)&i == 0x78 )
printf(“Little endian\n”);
}

Another way to test
#include "stdio.h"
int main()
{
union {
short s;
char c[sizeof(short)];
} un;
un.s = 0x0102;
if(sizeof(short) == 2)
{
if(un.c[0] == 1 && un.c[1] == 2)
printf("big-endian\n");
else if(un.c[0] == 2 && un.c[1] == 1)
printf("little-endian\n");
else
printf("unknown\n");
}
else
{
printf("sizeof(short) = %d\n", sizeof(short));
}
return(0);
}