Chainable boolean flags - what are they called?

user_12251738 0
Viewed 55

Frameworks I've seen before allow to pass a chain of multiple constants via a single parameter like So, I believe:

foo(FLAG_A | FLAG_B | FLAG_C);

They act like boolean so the function knows which flags have been given.

Now I want to implement something like that.

What is this concept called?

flags
3 Answers

It's based on binary-ORing. Normally, each of the symbolic constants will be just one distinct bit, e.g., as in:

enum {
   FLAG_A = 1,
   FLAG_B = 1<<1,
   FLAG_C = 1<<2,
};

so that you can than add them together with |, test for each individual one with & and subtract two such flag sets with & ~.

user_10847740

In .Net, these are defined by an enum using the FlagsAttribute:

[Flags()]
public enum Foo
{
     Bit1 = 1,
     Bit2 = 2,
     Bit4 = 4,
     Bit8 = 8,
     etc.
 }

// Or define using explicit binary syntax
[Flags()]
public enum Foo
{
     Bit1 = 0b_0000_0001,
     Bit2 = 0b_0000_0010,
     Bit4 = 0b_0000_0100,
     Bit8 = 0b_0000_,
     etc.
 }

And to utilise:

SomeFunction(Foo.Bit1 | Foo.Bit4 | etc);

I would suggest that your current name (Flags) seems to be the most appropriate definition, at least in this context.

user_21697620

Apparently "flags and bitmasks" are the right keywords to find more about this. "Flags" alone didn't before. Great thanks for the explanatory answers nevertheless!

user_122517380
Related