: operator in c/c++

Question

can anyone tell me, what is happening in this code. I tried to search a lot of places but couldn't understand what exactly is the commented part of the code doing.

#include<stdio.h>

struct XYZ {
    //int a:6; this one.
    char s; 
}structure;

int main() {
     printf("%lu",sizeof(structure)); 
     return 0;
}

I am getting the output as 4.

That's a [bit field](https://en.wikipedia.org/wiki/Bit_field). — Frédéric Hamidi, Jul 12 '13 at 14:51

score 4 · Answer 1 · answered Jul 12 '13 at 14:52

4

That line is commented out. It doesn't do anything.

If it wasn't commented out, it would mean that the size of int a is limited to 6 bits only. It's useful for bit-fields inside of a structure.

answered Jul 12 '13 at 14:52

viraptor

33,322
10
107
191

6 bits used and 2 bits reserved for another thing in the same byte ? – huseyin tugrul buyukisik Jul 12 '13 at 14:53
Which 6 bit? First or last in that structure? – huseyin tugrul buyukisik Jul 12 '13 at 14:54
1

@huseyintugrulbuyukisik You can check that yourself. Create struct with `int a:1;`, set `a` to 1 and look at the layout. I guess it depends if you're using big or little endian too. – viraptor Jul 12 '13 at 14:59

: operator in c/c++

1 Answers1