Is this virtual class defined in c++ standards?

[Anarki]

#include <iostream>
using namespace std;

virtual class Class {
public:
void fun() { cout << "Class::fun" << endl; }
};

int main() {
Class objClass;
cout << "Size of Class = " << sizeof(objClass) << endl;
cout << "Address of Class = " << &objClass << endl;
return 0;
}

normal size of class with no variables is 1 if there is a virtual
function size will be 4, but here the scenario is different its a
virtual class instead of virtual function. The program compiled
successfully in Visual Studio 2005. I expected a vptr to be inserted
in it. instead nothing like that. size of Class was 1 instead of 4. Is
this some kind of Undefined Behaviour?

 

[Neelesh Bodas]

#include <iostream>
using namespace std;

virtual class Class {
public:
void fun() { cout << "Class::fun" << endl; }

};

Std C++ doesnot allow "vitual" classes, it allows virtual functions
virtual inheritance.

 

[Neelesh Bodas]

#include <iostream>
using namespace std;

virtual class Class {
public:
void fun() { cout << "Class::fun" << endl; }

};

std C++ doesnot allow virtual classes.
It allows virtual functions and virtual inheritance.

 

[Rolf Magnus]

#include <iostream>
using namespace std;

virtual class Class {

That's a syntax error. You can't make classes virtual.

public:
void fun() { cout << "Class::fun" << endl; }
};

int main() {
Class objClass;
cout << "Size of Class = " << sizeof(objClass) << endl;
cout << "Address of Class = " << &objClass << endl;
return 0;
}

normal size of class with no variables is 1

Actually, it's some implementation-defined value that must not be zero.

if there is a virtual function size will be 4,

Again, this is some implementation-defined value.

but here the scenario is different its a virtual class instead of virtual
function. The program compiled successfully in Visual Studio 2005.

Then you probably didn't run it in standard C++ mode.

 

[Pete Becker]

Actually, it's some implementation-defined value that must not be zero.

Implementation-specific, but not implementation-defined.

--

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

 

[Kai-Uwe Bux]

Implementation-specific, but not implementation-defined.

I wonder, is it even guaranteed that there is a single value? or could
different classes all of which have no member variables have different
sizes?


Best

Kai-Uwe Bux

 

[Rolf Magnus]

IOW: It's unspecified.

I wonder, is it even guaranteed that there is a single value? or could
different classes all of which have no member variables have different
sizes?

They could all have different sizes. AFAICS, there is nothing in the C++
standard that forbids that.