C special syntax (adding ':' ) while defining a struct

Question

Possible Duplicate:
What does the : do in a struct declaration after a member

I would like to ask why the : character was added in this struct:

typedef union A
{
struct 
    {
        ubyte B:4;
         }
} struct_a;

Thanks in advance;

http://stackoverflow.com/questions/1675275/what-does-the-do-in-a-struct-declaration-after-a-member — GrahamS, Jun 28 '11 at 12:46
To all of you who answered this question, you should have closed it as duplicate. I'm pretty sure that there are a few dozen out there. — karlphillip, Jun 28 '11 at 12:50
@karlphillip: Or do both since there is no harm... sometimes it's quicker to answer the question and then find the duplicate. — Andrew White, Jun 28 '11 at 12:58
@karlphillip - reputation of 3000+ required to case a close vote. — borrible, Jun 28 '11 at 13:07
@borrible Thanks. But in the future remember that you still can upvote pertinent comments, like the one GrahamS left. — karlphillip, Jun 28 '11 at 13:10

score 4 · Answer 1 · answered Jun 28 '11 at 12:45

4

The :4 is putting a 4-bit limit on the variable. See Section 6.9 of Kernighan & Ritchie.

answered Jun 28 '11 at 12:45

borrible

score 3 · Answer 2 · answered Jun 28 '11 at 12:46

3

It's called a bit field. In this case it is saying the B is 4 bits in size.

answered Jun 28 '11 at 12:46

Andrew White

score 2 · Accepted Answer · answered Jun 28 '11 at 12:45

2

It declares a bit field with 4 bits.

answered Jun 28 '11 at 12:45

user786653

3 Answers3