MISRA C:1998 Rule 104 and rule 105

[derek_farn]

> What is the intended interpretation of Misra C:1998 rules 104 and 105?

Although the wording does not say so, I think the intent of these rules
is to apply to objects declared to have a pointer to function type.

> Misra C:1998 rule 104 reads \"Non-constant pointers to functions shall
> not be used\"

As written this rule prohibits the use of identifiers declared as functions.
For instance, in:

Code:

void f(void)
{ /* ... */ }

void g(void)
{
f(); /* this violates rule 104 since f has a non-constant pointer to function
       * type
       */
}

> Rule 105 reads: \"All the functions pointed to by a single pointer to
> function shall be identical in the number and type of parameters and
> the return type\".

I think the intent was to say:

\"All functions pointed to by an object having a pointer to function
type shall ...\"

> We interpret rule 105 as it is allowed for one single function pointer to
> point at diffferent functions during runtime. But with the conservative
> interpretation of rule 104, a function pointer may never change the
> function it points at during runtime and thus conflicts with rule 105, i.e.
> rule 105 would be superfluous.

Rule 105 is needed to stop me writing:

Code:

extern int f(int, long);
extern char g(float);

/* ... */
some_call((int (* const)(int))f);
some_call((int (* const)(int))g);

Rule 104 only requeries the use of const, it does not
say anything about or parameter types.