cast

[Lenin]

Hi,
I have a multiply inherited class "C" as folloows. None of
them are inherited as virtual base class except that they have virtual
functions.

class b1
{
....
virtual void f1() {}
}

class b2
{
....
virtual void f2() {}
}

class c: pulbic b1, public b2
{
.....
}

Now that, I have a function fun() which takes b1's pointer and now
I want to call b2's functions from there. Assume that the function
is called with argument as address of c's object like below.

void fun(b1 *bp1)
{
b2 *bp2 = (b2*) (c*) bp1;
bp2->f2();
}


somewhere I call like this

c obj;
fun(&obj);

This works fine. But in this case, do I need to use dynamic cast
inside the function fun? Assume that the runtime error check for junk
pointer is not needed in my case.

Thanks in advance.

[Pete Becker]

Re: cast

On 2008-10-08 05:52:43 -0400, Lenin <lenin@veveo.ne tsaid:

Hi,
I have a multiply inherited class "C" as folloows. None of
them are inherited as virtual base class except that they have virtual
functions.
>
class b1
{
...
virtual void f1() {}
}
>
class b2
{
...
virtual void f2() {}
}
>
class c: pulbic b1, public b2
{
....
}
>
Now that, I have a function fun() which takes b1's pointer and now
I want to call b2's functions from there.

Seems like the function ought to take a c*. Then you won't have to mess
around with conversions.

Assume that the function
is called with argument as address of c's object like below.
>
void fun(b1 *bp1)
{
b2 *bp2 = (b2*) (c*) bp1;
bp2->f2();
}
>
>
somewhere I call like this
>
c obj;
fun(&obj);
>
This works fine. But in this case, do I need to use dynamic cast
inside the function fun? Assume that the runtime error check for junk
pointer is not needed in my case.
>

If you'll always be able to convert a b1* to a b2*, then you can use
the C style casts as written above, replace them with static_casts, or
write the function so that it's interface tells the truth. If it only
deals with c*'s, then it should take a c* as its argument.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Lenin]

Re: cast

Lets say the function fun and the b1,b2 class are part of some library
and fun is a callback. Then in that case, will the c style casting
works irrespective of the compiler/platform?

On Oct 8, 3:16 pm, Pete Becker <p...@versatile coding.comwrote :

On 2008-10-08 05:52:43 -0400, Lenin <le...@veveo.ne tsaid:
>
>
>
>
>

Hi,
       I have a multiply inherited class "C" as folloows.   None of
them are inherited as virtual base class except that they have virtual
functions.

>

class b1
{
...
virtual void f1() {}
}

>

class b2
{
...
virtual void f2() {}
}

>

class c: pulbic b1, public b2
{
....
}

>

    Now that, I have a function fun() which takes b1's pointer and now
I want to call b2's functions from there.

>
Seems like the function ought to take a c*. Then you won't have to mess
around with conversions.
>
>
>
>
>

   Assume   that the function
is called with argument as address of c's object like below.

>

void fun(b1 *bp1)
{
   b2 *bp2 = (b2*) (c*) bp1;
   bp2->f2();
}

>

somewhere I call like this

>

c obj;
fun(&obj);

>

This works fine. But in this case, do I need to use dynamic cast
inside the function fun?  Assume that the runtime error check for junk
pointer is not needed in my case.

>
If you'll always be able to convert a b1* to a b2*, then you can use
the C style casts as written above, replace them with static_casts, or
write the function so that it's interface tells the truth. If it only
deals with c*'s, then it should take a c* as its argument.
>
--
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)