inheritance - problem with identyfing object

[jacek]

I have a:
class A
and a:
class B : public A

then I have a:
vector<A*> v;
which contains objects of both A and B classes.

when doing
for (int i=0; i<v.size(); i++)
{
}
I want to identify if each v is an object of class A or B.
sizeof(A) and sizeof(B) give the same unfortunately.
any hints?

jacek

 

[Jeff Schwab]

I have a:
class A
and a:
class B : public A

then I have a:
vector<A*> v;
which contains objects of both A and B classes.

when doing
for (int i=0; i<v.size(); i++)
{
}
I want to identify if each v is an object of class A or B.
sizeof(A) and sizeof(B) give the same unfortunately.
any hints?

jacek

My preferred method would be to give class A a public virtual
"is_subclass" method returning false, and override the method in class B
to return true. An alternative is to use dynamic_cast; see your
favorite C++ reference for details.

 

[Victor Bazarov]

I have a:
class A
and a:
class B : public A

then I have a:
vector<A*> v;
which contains objects of both A and B classes.

when doing
for (int i=0; i<v.size(); i++)
{
}
I want to identify if each v is an object of class A or B.
sizeof(A) and sizeof(B) give the same unfortunately.
any hints?

jacek

My preferred method would be to give class A a public virtual
"is_subclass" method returning false, and override the method in class B
to return true. An alternative is to use dynamic_cast; see your
favorite C++ reference for details.

I'd say that anybody's preferred method should be to re-examine the need
to identify the actual type. If you store them in one vector, you must
have had a reason. That reason ought to have told you that you need to
have polymorphic behaviour instead of finding out what type the pointers
point to.

Victor

 

[Jeff Schwab]

I have a:
class A
and a:
class B : public A

then I have a:
vector<A*> v;
which contains objects of both A and B classes.

when doing
for (int i=0; i<v.size(); i++)
{
}
I want to identify if each v is an object of class A or B.
sizeof(A) and sizeof(B) give the same unfortunately.
any hints?

jacek

My preferred method would be to give class A a public virtual
"is_subclass" method returning false, and override the method in class B
to return true. An alternative is to use dynamic_cast; see your
favorite C++ reference for details.

I'd say that anybody's preferred method should be to re-examine the need
to identify the actual type. If you store them in one vector, you must
have had a reason. That reason ought to have told you that you need to
have polymorphic behaviour instead of finding out what type the pointers
point to.

Good point, Victor. Of course, I agree.

 

[jacek]

Jeff and Victor,
thanks for all help!
you're absolutely right about polymorphism, I'm gonna refactor the source
code when I have more time, hopefully tomorrow

jacek

 

[bartek]

I have a:
class A
and a:
class B : public A

then I have a:
vector<A*> v;
which contains objects of both A and B classes.

when doing
for (int i=0; i<v.size(); i++)
{
}
I want to identify if each v is an object of class A or B.
sizeof(A) and sizeof(B) give the same unfortunately.
any hints?

Visitor pattern, maybe?

'zdrowka!