why not virtual ctors?? 2

[ila]

Hi,

why cant you make a CTOR virtual??
if there is a need to make a CTOR virtual..
what is stopping C++ from giving this option??

thanks
lak

 

[Cagliostro]

A class can require something necessary operations, which you mustn't turn off. John Fill

 

[ila]

John,

Thats what i am asking..
what are the necessary operations which block this
functionality??

Thanks
lak

 

[Cagliostro]

It is up to whome has implemented this base class. The programmer who implements a inherited class usualy do not know what to initialize, which variable to change and many details. He know only some properties of it.
This mecanisme assure what the base class will be properly initialized. John Fill

 

[abp]

The responsibility for creating an object of a class is
with the class's constructor. If you dont know, C++ compilers always create a default constructor if the programmer doesnt specify one in his declaration.

Declaring a constructor as 'virtual' violates the integrity of a class, since the derived class can then make changes in
the way the base class is constructed. Hence it is never
allowed.

In short, constructors are never virtual to make sure base classes are properly created(constructed). On the other hand destructors can be virtual or pure virtual.