Codejock Developer Community : ~CXTPControlCustom() should be virtual!

~CXTPControlCustom() should be virtual! : Hi :) See 10.3.2 from this...

Tue, 14 Apr 2009 12:48:11 +0000

Author: Oleg
Subject: 13978
Posted: 14 April 2009 at 12:48pm

Hi :)

See 10.3.2 from this standard.

ok, think we find out that ~CXTPControlCustom is virtual even without virtual keword. so discussion can be closed.

~CXTPControlCustom() should be virtual! : Ok, so the destructor in A saves...

Tue, 14 Apr 2009 10:49:10 +0000

Author: znakeeye
Subject: 13978
Posted: 14 April 2009 at 10:49am

Ok, so the destructor in A saves you in this case, but that doesn't motivate leaving out the "virtual" keyword. I ain't gonna compete with my master (though Anakin will become stronger one day).

However...

International Standard ISO/IEC 14882: http://www.gisinvestor.ru/?module=File&action=Download&id=8

If the object being deleted has incomplete class type at the point of deletion and the complete class has a nontrivial destructor or a deallocation function the behavior is undefined.

Q: Why would you NOT explicitly make the destructor virtual? If CXTPControlCustom was some day changed to inherit some other class there is a high risk the class causes problems when derived!

My answer: Public destructors should always be explicitly declared virtual. Just like you check pointers before using them, this is a way to avoid problems.

~CXTPControlCustom() should be virtual! : Virtual **** comparison!!!

Tue, 14 Apr 2009 09:01:53 +0000

Author: ABuenger
Subject: 13978
Posted: 14 April 2009 at 9:01am

Virtual **** comparison!!!

~CXTPControlCustom() should be virtual! : Hi, So you want to compete...

Tue, 14 Apr 2009 08:33:07 +0000

Author: Oleg
Subject: 13978
Posted: 14 April 2009 at 8:33am

Hi,

So you want to compete in C++ knowledge ? :)

www.brainbench.com -> C++ Fundametals.

Test:	C++ Fundamentals
Date:	10-Feb-2009
Score:	4.76
Weights:	100% C++ Fundamentals
Elapsed time:	49 min 19 sec

C++ Fundamentals
Score:	4.76
Percentile:	Scored higher than 97% of previous examinees

Demonstrates understanding of most advanced concepts within the subject area. Appears capable of mentoring others on the most complex projects.
Strong Areas	Data Handling Flow Control Functions Building C++ Programs Templates
Weak Areas	None noted

try to score more :)

ps. I bet 100$ that you didn't try last sample.

Try this.

struct A
{
A() {}
virtual ~A() {printf("Called ~A\n");}
};

struct B : public A
{
B() {}
~B() { printf("Called ~B\n");} // destructor B will be virtual even without virtual keyword
};

struct C : public B
{
~C() { printf("Called ~C\n");} // destructor B will be virtual even without virtual keyword

};

int main(int argc, char* argv[])
{

B *b = new C;
delete b; // no leak. no crash.

return 0;
}

~CXTPControlCustom() should be virtual! : Yes, of course. But... struct...

Tue, 14 Apr 2009 03:46:36 +0000

Author: znakeeye
Subject: 13978
Posted: 14 April 2009 at 3:46am

Yes, of course. But...

struct C : public B

{

};

B *b = new C;

delete b; // leak or crash

Public destructors should always be declared virtual, period.

~CXTPControlCustom() should be virtual! : Try this sample struct A { ...

Tue, 14 Apr 2009 00:43:36 +0000

Author: Oleg
Subject: 13978
Posted: 14 April 2009 at 12:43am

Try this sample

struct A

{

A() {}

virtual ~A() {}

};

struct B : public A

{

B() {}

~B() {} // destructor B will be virtual even without virtual keyword

};

A *a = new B;

delete a;

Trust me, I now what is "virtual" keyword and how it used :)

p.s. See 10.3.1 of ANSI C++ International Standard

~CXTPControlCustom() should be virtual! : That depends on how you use it....

Mon, 13 Apr 2009 14:55:51 +0000

Author: znakeeye
Subject: 13978
Posted: 13 April 2009 at 2:55pm

That depends on how you use it. The code is dangerous. Try this sample:

struct A

{

A() {}

~A() {}

};

struct B : public A

{

B() {}

virtual ~B() {} // Correctly written, derived class.

};

A *a = new B;

delete a; <--- crash!

Trust me, the "virtual" keyword is extremely important!

~CXTPControlCustom() should be virtual! : Hi, If there is no "virtual"...

Fri, 10 Apr 2009 15:59:36 +0000

Author: Oleg
Subject: 13978
Posted: 10 April 2009 at 3:59pm

Hi,

If there is no "virtual" keyword it doesn't mean its not virtual ;-)

ps. Don't worry, its virtual.

~CXTPControlCustom() should be virtual! : Quite important actually.

Fri, 10 Apr 2009 14:35:53 +0000

Author: znakeeye
Subject: 13978
Posted: 10 April 2009 at 2:35pm

Quite important actually.