Is '!!' an existing operator in C?

Question

While going over infrastructure code, I found this:

return !!(fin.flags & FIN_ACCEPT);

Does this has a meaning other than two logical nots in succession?

No. Take a look at any reference on "C operators". – Oliver Charlesworth Sep 07 '14 at 10:20 — Oliver Charlesworth, Sep 07 '14 at 10:20

score 4 · Accepted Answer · answered Sep 07 '14 at 10:22

4

! is logical negation. !! is logical negation applied twice.

It is typically used to normalise a boolean expression value to be either 0 or 1.

answered Sep 07 '14 at 10:22

David Heffernan

2

Also known as normalization of a truth-value. – Deduplicator Sep 07 '14 at 10:24

Igor · Answer 2 · 2014-09-07T10:26:38.593

1

It is used to turn a numerical value into a boolean value. For example:

a = 5;
a = !!a;

!(!a)---> !(!5) ----> !(0) ----> 1

a will have value 1.

edited Sep 07 '14 at 10:26

answered Sep 07 '14 at 10:21

Igor

2

Check wheter the variable is version-controlled? Or what do you mean with revertability? – Deduplicator Sep 07 '14 at 10:26

2 Answers2