inheritance and assignment

[Vasileios Zografos]

Hi everyone,

ok assume that I have a class named Vertex3D with 3 simple member
variables x,y,z.
and I create a child class named SpecialVertex3D that has an extra
variable E.

can I do something like

Vertex3D v1;
SpecialVertex3D s1;
s1=v1;

???

Well, my compiler complains so probably I cannot. any other way apart
from creating an "operator=" method?

[Victor Bazarov]

"Vasileios Zografos" <vz*******@bcs.org.uk> wrote...

ok assume that I have a class named Vertex3D with 3 simple member
variables x,y,z.
and I create a child class named SpecialVertex3D that has an extra
variable E.

can I do something like

Vertex3D v1;
SpecialVertex3D s1;
s1=v1;

???
Not unless you define how it should be done. The default operator=
calls respective operator= functions for every member. 'v1' does
not have member 'E'. How should the compiler assign 's1.E'?

Well, my compiler complains so probably I cannot. any other way apart
from creating an "operator=" method?

No.

Victor

[John Tsiombikas (Nuclear / the Lab)]

Vasileios Zografos wrote:

Hi everyone,

ok assume that I have a class named Vertex3D with 3 simple member
variables x,y,z.
and I create a child class named SpecialVertex3D that has an extra
variable E.

can I do something like

Vertex3D v1;
SpecialVertex3D s1;
s1=v1;

If you're aiming for polymorphism (as it seems from the fact that you
specifically said you're talking about two classes in a hierarchy) it
works only through pointers, e.g. you can assign a pointer to
SpecialVertex3D to a pointer to Vertex3D.

Otherwise overload an operator= if you just want to make a copy of a
Vertex3D's member variables to the corresponding ones in
SpecialVertex3D.. (or whatever you think fitting anyway).

Giannis Tsiombikas
-- Nuclear / the Lab --

[Victor Bazarov]

"Rolf Magnus" <ra******@t-online.de> wrote...

Victor Bazarov wrote:

"Vasileios Zografos" <vz*******@bcs.org.uk> wrote...

ok assume that I have a class named Vertex3D with 3 simple member
variables x,y,z.
and I create a child class named SpecialVertex3D that has an extra
variable E.

can I do something like

Vertex3D v1;
SpecialVertex3D s1;
s1=v1;

???

Not unless you define how it should be done. The default operator=
calls respective operator= functions for every member. 'v1' does
not have member 'E'. How should the compiler assign 's1.E'?

Well, my compiler complains so probably I cannot. any other way apart
from creating an "operator=" method?

No.

What about a conversion constructor or operator?

You're right. Those would probably work too.

V