polymorphic class have diferent size on different os

[mangesh]

class B
{
public :
void f() = 0 ;
};

class D : public B
{
public :
void f()
{

}
};

int main()
{
D d ;
int s = sizeof(d);
return 0 ;
}

now value of s will be different on windows and unix , why so ?

 

[Ian Collins]

class B
{
public :
void f() = 0 ;

This isn't valid, virtual keyword is missing.

};

class D : public B
{
public :
void f()
{

}
};

int main()
{
D d ;
int s = sizeof(d);
return 0 ;
}

now value of s will be different on windows and unix , why so ?

Who says they should be the same?

 

[Salt_Peter]

class B
{
public :
void f() = 0 ;

virtual void f() = 0;

};

class D : public B
{
public :
void f()
{

}
};

int main()
{
D d ;
int s = sizeof(d);
return 0 ;
}

now value of s will be different on windows and unix , why so ?

Unix is a 64 bit OS and your windows is probably 32 bit.
Regardless, a real programmer must not write code that depends on the
platform beneath.
Hence: what you see is expected and inconsequential.

 

[Ron Natalie]

now value of s will be different on windows and unix , why so ?

There's not even any guarantee that s will be the same value on
different implementations within UNIX or Windows.

 

[Frederick Gotham]

mangesh posted:

now value of s will be different on windows and unix , why so ?

Three reasons:


(1) The amount of bytes consumed by primitive types is implementation-
specific.
(2) The amount and placement of padding within an object is
implementation-specific.
(3) The way in which virtual functions are implemented is
implementation-specific.

 

[mangesh]

Hi ,
thanks for detailed reply .

Regards ,
Mangesh Sawant .