Can constructors & destructor be virtual

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Can constructors & destructor be virtual ?

and one more question

write function push () of stack that it doubles the length of the array when the array is full

Posted 12-Oct-11 19:01pm

kschandru

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Philippe Mori 13-Oct-11 8:22am

Why ask 2 unrelated questions in the same question?

Albert Holguin 13-Oct-11 10:59am

If I could upvote this I would...

Chuck O'Toole 13-Oct-11 10:12am

Sounds like either a test or an interview question(s)

2 solutions

Solution 2

Destructor — yes. This is the first explanation of this matter I found: http://www.programmerinterview.com/index.php/c-cplusplus/virtual-destructors/[^].

Constructor?.. Yes, in some languages, never in C++. Same thing about static functions, by the way. The conception of virtual constructors and static functions is extremely powerful, maybe too powerful for C++. I miss it.

The implementation of push I would leave you for a easy home assignment (also, you did not clearly formulate this little problem). Pretty useful exercise, anyway.

Good luck,

—SA

Posted 12-Oct-11 19:10pm

Sergey Alexandrovich Kryukov

Updated 12-Oct-11 19:12pm

v2

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Espen Harlinn 13-Oct-11 17:52pm

5'ed!

Sergey Alexandrovich Kryukov 13-Oct-11 19:40pm

Thank you, Espen.
--SA

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Prerak Patel · Accepted Answer · 2011-10-12T19:08:00

Solution 1

To build an object the constructor must be of the same type as the object and because of this a constructor cannot be a virtual function. But the same thing does not apply to destructors. A destructor can be defined as virtual or even pure virtual. You would use a virtual destructor if you ever expect a derived class to be destroyed through a pointer to the base class. This will ensure that the destructor of the most derived classes will get called.
Ref: http://www.cprogramming.com/tutorial/constructor_destructor_ordering.html[^]

Try the programming part yourself first.

Posted 12-Oct-11 19:08pm

Prerak Patel

Updated 13-Oct-11 0:34am

v2

Comments

Sergey Alexandrovich Kryukov 13-Oct-11 15:13pm

All correct. I only add this does not have to apply to other languages. This is not a universal OOP rule. I think C++ approach is limited as virtual constructors and static methods make perfect sense as well as inheritance from a static class. This is because a class itself actually exists like an object, it if has virtual table and/or RTTI -- all these things belong to a whole class and put in some invisible object (a meta-class), which may or may not be exposed. In C++, it physically exists but either not exposed or exposed only to RTTI.
--SA

Espen Harlinn 13-Oct-11 17:52pm

5'ed!