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byte ordering         Technical information         byte ordering




Machine-dependent ordering of bytes


Byte ordering  is the order in which a  given machine stores suc-
cessive bytes of a multibyte data item.  Different machines order
bytes differently.

The following example displays  a few simple examples of byte or-
dering:


main()
{
        union
        {
                char b[4];
                int i[2];
                long l;
        } u;
        u.l = 0x12345678L;



        printf("%x %x %x %x\n",
                u.b[0], u.b[1], u.b[2], u.b[3]);
        printf("%x %x\n", u.i[0], u.i[1]);
        printf("%lx\n", u.l);
}


When run  on ``big-endian'' machines,  such as the  M68000 or the
Z8000, the program gives the following results:


        12 34 56 78
        1234 5678
        12345678


As you  can see, the  order of bytes  and words from  low to high
memory is the same as is represented on the screen.

However, when this  program is run on ``little-endian'' machines,
such as the PDP-11, you see these results:


        34 12 78 56
        1234 5678
        12345678


As  you can  see, the  PDP-11 inverts the  order of  bytes within
words in memory.



COHERENT Lexicon                                           Page 1




byte ordering         Technical information         byte ordering



Finally,  when the  program is  run  on the  i8086 you  see these
results:


        78 56 34 12
        5678 1234
        12345678


The i8086 inverts both words and long words.

***** See Also *****

C language, canon.h, data formats, technical information











































COHERENT Lexicon                                           Page 2

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