Logical equality in C

Question

[It seems odd this doesn't exist, so apologies in advance if it's a duplicate]

I want to test for logical equality in C. In other words, I want to know whether two values would be equal if both were converted in the normal way associated with logical expressions.

In C99, I think that

(bool)a == (bool)b

gives what I want. Is that correct? What is the normal way of writing this in traditional C?

Answer 1

You typically see this:

if ((a == 0) == (b == 0))

Or

if (!!a == !!b)

Since !!a evaluates to 1 if a is nonzero and 0 otherwise.

Hope this helps!

Answer 2

In C, zero is false. If you want to convert any value to its boolean equivalent, the standard way (well, except that there's almost never a need for it) is to prefix an expression with !! , as in !!a. In the case of your expression, !!a == !!b may be simplified to !a == !b

Answer 3

In pre-C99 C, the tradiitional, idiomatic way to "cast to bool" is with !!.