What do you call this: "unsigned int a_bit : 1;"? Is there use outside of bit fields?

Question

So I was working with bit fields, when I started thinking that when you create a bit field, for example

struct bit_field{
  unsigned int just_a_bit : 1;
  unsigned int five_bits  : 5;
  unsigned int            : 3; //Fill to 8 bits
}

You use unsigned int variable : bits;, what is this called (so I can search it)? Can this be used outside of creating bit fields, and would there be any point in doing so?

For clarity, by "this" I mean using colon with size in bits after the variable name whilst creating a variable.

So wait, I thought the entire struct was called bit field, but it's actually the `unsigned int just_a_bit : 1;` that's called a bit field? — YellowPeak, Oct 16 '15 at 19:07
No a struct is a struct. the thing inside the struct is called a bit field. — NathanOliver, Oct 16 '15 at 19:09

score 4 · Answer 1 · edited May 23 '17 at 11:44

4

That is simply called a "bit-field". It's only allowed within a struct (or a union, though it's of limited use in a union).

edited May 23 '17 at 11:44

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answered Oct 16 '15 at 19:00

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score 1 · Accepted Answer · answered Oct 16 '15 at 19:09

1

The members are bitfields.

The encapsulating class is still just a class.

answered Oct 16 '15 at 19:09

Lightness Races in Orbit

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Ahhhh, I see. This was the source of my confusion – YellowPeak Oct 16 '15 at 19:12

What do you call this: "unsigned int a_bit : 1;"? Is there use outside of bit fields?

2 Answers2