Engineered bool compares equal to both true and false, why?

Question

The example bellows compiles, but the output is rather strange :

#include 
#include 

struct A
{
    int a;
    char b;
    bo         


        

Answer 1

I can't seem to find anything in the standard that indicates why this would happen (most possibly my fault here) -- this does include the reference provided by 7vies, which is not in itself very helpful. It is definitely undefined behavior, but I can't explain the specific behavior that is observed by the OP.

As a practical matter, I 'm very surprised that the output is

true
true

Using VS2010, the output is the much more easy to explain:

false
false

In this latter case, what happens is:

• comparisons to boolean true are implemented by the compiler as tests for equality to 0x01, and since 0xff != 0x01 the result is false.
• same goes for comparisons to boolean false, only the value compared with is now 0x00.

I can't think of any implementation detail that would cause false to compared equal to the value 0xff when interpreted as bool. Anyone have any ideas about that?