I can typedef char to CHAR1 which is 8 bits.
But how can I make 3 bit variable as datatype?
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Jay Bosamiya
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Ishmeet
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2Why a three bit routine? Computers are happier with bytes – Ed Heal Jul 10 '15 at 11:22
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3Sounds like a [X-Y problem](http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem). What exactly are you trying to achieve? – Yu Hao Jul 10 '15 at 11:23
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@EdHeal I want to use them as CoS (Class of Service), as they are 3 bits. – Ishmeet Jul 10 '15 at 11:23
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If negative comments are coming, I am deleting this question. – Ishmeet Jul 10 '15 at 11:26
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1You do not need to use all eight bits. – Ed Heal Jul 10 '15 at 11:27
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3Side note : `char` is not always 8 bits. – Quentin Jul 10 '15 at 11:28
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@Quentin - Granted - but in most cases it is – Ed Heal Jul 10 '15 at 11:30
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@Quentin How is `char` not always 8 bits. Can you please describe? – Ishmeet Jul 10 '15 at 11:39
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1@Ishmeet: There is already an SO question for that http://stackoverflow.com/questions/881894/is-char-guaranteed-to-be-exactly-8-bit-long – Jay Bosamiya Jul 10 '15 at 11:41
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Some people like to hold onto the past. Some machines had 7 bits with the eight bit being parity. – Ed Heal Jul 10 '15 at 11:43
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[10 or 12 bit field data type](http://stackoverflow.com/q/29529979/995714), [Which C datatype can represent a 40-bit binary number?](http://stackoverflow.com/q/9595225/995714) – phuclv Apr 01 '17 at 02:45
3 Answers
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You might want to do something similar to the following:
struct
{
.
.
.
unsigned int fieldof3bits : 3;
.
.
.
} newdatatypename;
In this case, the fieldof3bits takes up 3 bits in the structure (based upon how you define everything else, the size of structure might vary though).
This usage is something called a bit field.
From Wikipedia:
A bit field is a term used in computer programming to store multiple, logical, neighboring bits, where each of the sets of bits, and single bits can be addressed. A bit field is most commonly used to represent integral types of known, fixed bit-width.
Jay Bosamiya
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1It's also one of the most obscure core-language features of C, so it's best employed when you really can't do without it. – Matteo Italia Jul 10 '15 at 11:37
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In the case of certain protocols etc (which require specific sized fields), is probably the only proper use I can think of for it. – Jay Bosamiya Jul 10 '15 at 11:39
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It seems you're asking for bitfields https://en.wikipedia.org/wiki/Bit_field Just be aware that for some cases it's can be safer just use char or unsigned char instead of bits (compiler specific, physical memory layout etc.)
Happy coding!
Yury Schkatula
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typedef struct {
int a:3;
}hello;
It is only possible when it is inside structure else it is not
Sohil Omer
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