Get single bytes from a word

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How to get the value of individual bytes of a variable?

How can I get single bytes from a word (for example an unsigned int in C) without using bit-wise operations (that is using arithmetic operations?)

I don't know why, but this formula (C-Like) for an x number doesn't seem to work:

floor(x / pow(R, i)) % R

where R is the radix with which the number is represented, and i is used to indicate the i-th byte to obtain.

Any particular reason why you don't want to use bitwise operators? — Corbin, May 21 '12 at 19:56
This is your 6th question. You have accepted no answers and never voted. Please read the [faq] and make an effort to give back to the community from which you ask for help. — David Heffernan, May 21 '12 at 19:57

score 1 · Accepted Answer · answered May 21 '12 at 19:56

1

If you really need to avoid bitwise operations, you can cheat alternatively (beware if you're using a little or big endian machine!):

char *int_16_storage;
uint16_t the_word = 0xabcd;
int_16_storage = &the_word;

uint8_t low_byte = int_16_storage[0];
uint8_t high_byte = int_16_storage[1];

answered May 21 '12 at 19:56

Could also be done using a union, which doesn't rely on pointers to work. – Richard J. Ross III May 21 '12 at 20:03
What's the problem with pointers? – May 21 '12 at 20:03
Nothing is 'wrong' with pointers, but they can make code harder to read. With a union, it is much easier to determine what you are accomplishing. – Richard J. Ross III May 21 '12 at 20:05
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On the other hand, such use of unions is undefined and distinctly non-portable. – David Heffernan May 21 '12 at 20:06
@DavidHeffernan "non-portable", yes. "Undefined", not in C90 and not in C99TC3 as clarified by footnote 82. – Pascal Cuoq May 21 '12 at 20:11

Get single bytes from a word

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