Unpermitted operand to operator '!' [MISRA 2012 Rule 10.1, required] - c

Question

Observing below Misra warning for below part of code.
Unpermitted operand to operator '!' [MISRA 2012 Rule 10.1, required]
Not sure what could be the fix here to get rid of this warning.
#define C_BYTE unsigned char
C_BYTE SessionStatus;
#define DISCONNECTED 0x10
if((!(SessionStatus & (C_BYTE) DISCONNECTED)))
{
//Do something
}
I tried a few chances but didn't work as below.
1)
if((~(SessionStatus & (C_BYTE) DISCONNECTED)))
{
//Do something
}
2)
if((!(SessionStatus & (C_BYTE) DISCONNECTED)) != 0u)
{
//Do something
}

Answer 1

The reason for the warning is that MISRA-C rule 10.1 expects the operand to the ! && || operators to be "essentially boolean". In your case it is actually an int, because of implicit type promotion rules.
Your 2nd example almost solved it, but you must convert to essentially boolean before applying !. That is:
if(!( (SessionStatus & (C_BYTE)DISCONNECTED) != 0u ))
This is ok since the result of the != operator is to be regarded as essentially boolean. So that code is MISRA-C compliant, but a bit hard to read. I would instead recommend this:
#define DISCONNECTED 0x10u // u suffix makes this essentially unsigned
...
bool disconnected = (bool) (SessionStatus & DISCONNECTED);
if(!disconnected)
By adding the u suffix to the integer constant, it is essentially unsigned, same type category as unsigned char. Therefore the & operation is valid without using any casts. However, we are not allowed to implicitly convert from essentially unsigned to essentially boolean, therefore add the cast to bool.
EDIT
Since SessionStatus & DISCONNECTED is a "composite expression", MISRA doesn't allow the result to be assigned or cast to a different or wider essential type. The rationale is that they fear incompetent programmers who believe that the calculation in for example (uint32_t)(u16a + u16b) is carried out with uint32_t because of the cast, which is of course nonsense. (It would be better to educate the programmers about basic C than to come up with artificial rules, but anyway...)
I'd advise to ignore this rule entirely, but if you can't for whatever reason, here's an alternative fix:
#define DISCONNECTED 0x10u
...
unsigned char disconnected = SessionStatus & DISCONNECTED;
if(!(bool)disconnected)
But of course this is worse code than my first example.