What does it means int i:3 in variable assignment?

Question

I'm trying to understand the following code in C:

struct values{
  int i:3;
  int j:3;
  int k:2;
};

int main(){
    struct values v = {-6,2,5};
    printf("%d %d %d", v.i,v.j,v.k);
}

This code produces the following output:

2 2 1

I'm trying to understand what does it mean the assignment for int values used inside the struct i.e.: int i:3 ?

I know that : is not an operator. So what does it do? Also, can someone explain how this output is achieved?

Thanks very much!

its declaring a bit-field, see here: https://en.wikipedia.org/wiki/Bit_field — thurizas, Mar 23 '16 at 23:13
Why do you call it "assignment"? Where do you see any similarity to "assignment" here? — AnT, Mar 23 '16 at 23:15
My mistake calling it assignement. It was my first impression but I really had no idea of the meaning. Thanks for giving me the right place to look! — clasimoes, Mar 24 '16 at 01:29

score 1 · Accepted Answer · edited May 23 '17 at 12:31

1

The numbers specifies the length in bits for each field.

Hence i and j are represented in 3 bits while k in 2 bits.

By the way this is question is clearly a duplicate of this question and there's a very good answer I suggest you to read.

edited May 23 '17 at 12:31

Community

answered Mar 23 '16 at 23:14

fredmaggiowski

downvoter can let me know why? – fredmaggiowski Mar 23 '16 at 23:23
2

It wasn't me but perhaps the downvoter though you should have voted to close as a duplicate *instead of* posting an answer. – Keith Thompson Mar 23 '16 at 23:24
1

Oh well, i've actually flagged the question as duplicate, anyhow I thought that it could be helpful for OP to have a direct hint.. – fredmaggiowski Mar 23 '16 at 23:26

1 Answers1