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Dennis Jones wrote:

> > Frank-O wrote:
> > static A * a;

Must be initialized at least to NULL, else you get access to random
memory area due to "a" can be placed to uninitialized memory area
filled with random values.

> > printf(" a is ", a->Display());

> I do not believe that is true. a->Display() is not actually "dereferencing"
> the pointer. The Display() method exists regardless of whether or not any
> instances of 'A' are created, and it will get invoked via a->, regardless of
> the value of 'a'.

If member Display() is virtual, it can not be called for NULL pointer,
because class of real object can not be found.

> I suppose it is possible that calling a method through an invalid pointer
> may result in undefined behavior in some implementations, but on every
> compiler I have used, class methods are always available and callable
> through uninitialized and NULL pointers -- you just have no way of knowing
> what will happen if you try to access memory through the 'this' pointer.

What is the reason to call member for NULL pointer? I think any
compiler can treat the calling as error, similar to stack overflow
check and other runtime checks, and compiler do not check for NULL
pointer only for perfomance requirements.

Frank-O wrote:
> class A
> {
> int dCol;
> public :
> const char * Display(void) const { return this==NULL ? "A" : "B" ; }
>
> };
>
> int main(void)
> {
>
> static A * a;
> printf(" a is ", a->Display());
>
> return 0;
>
> }
>
> it prints A
>
> I don' t understand why the pointer value is necessary NULL ?

Incidentally, there is a pop song called "Monster" by The Automatic
which includes the line "You can't avoid static abuse". Presumably this
is what they were thinking of when they wrote it...

Dennis Jones wrote:
> "Kai-Uwe Bux" <> wrote in message
> news:eo3h2o$oam$...
> > Frank-O wrote:
> >
> >> class A
> >> {
> >> int dCol;
> >> public :
> >> const char * Display(void) const { return this==NULL ? "A" : "B" ; }
> >>
> >> };
> >>
> >> int main(void)
> >> {
> >>
> >> static A * a;
> >> printf(" a is ", a->Display());
> >>
> >> return 0;
> >>
> >> }
> >>
> >> it prints A
> >
> > It may print anything: "a->Display()" dereferences an uninitialized
> > pointer
> > variable. The program has undefined behavior.
>
> I do not believe that is true. a->Display() is not actually "dereferencing"
> the pointer. The Display() method exists regardless of whether or not any
> instances of 'A' are created, and it will get invoked via a->, regardless of
> the value of 'a'. That is, the ability to call methods in the class is not
> dependent on having a valid, non-NULL pointer.

Suppose A contained one or more virtual functions. Wouldn't the
compiler be likely to read the object, in order to find a vtable?

Or are you relying on the compiler spotting that there are no virtual
functions and so not attempting to use the vtable mechanism?