~CXTPControlCustom() should be virtual!
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URL: http://forum.codejock.com/forum_posts.asp?TID=13978
Printed Date: 22 June 2025 at 6:41pm
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Topic: ~CXTPControlCustom() should be virtual!
Posted By: znakeeye
Subject: ~CXTPControlCustom() should be virtual!
Date Posted: 10 April 2009 at 2:35pm
|
Quite important actually. ------------- PokerMemento - http://www.pokermemento.com/ |
Replies:
Posted By: Oleg
Date 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. ------------- Oleg, Support Team CODEJOCK SOFTWARE SOLUTIONS |
Posted By: znakeeye
Date 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! ------------- PokerMemento - http://www.pokermemento.com/ |
Posted By: Oleg
Date 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 ------------- Oleg, Support Team CODEJOCK SOFTWARE SOLUTIONS |
Posted By: znakeeye
Date 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.  ------------- PokerMemento - http://www.pokermemento.com/ |
Posted By: Oleg
Date Posted: 14 April 2009 at 8:33am
|
Hi,
So you want to compete in C++ knowledge ? :)
http://www.brainbench.com - www.brainbench.com -> C++ Fundametals.
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;
} ------------- Oleg, Support Team CODEJOCK SOFTWARE SOLUTIONS |
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Posted By: ABuenger
Date Posted: 14 April 2009 at 9:01am
Virtual **** comparison!!!  ------------- Codejock support |
Posted By: znakeeye
Date 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 - 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. ------------- PokerMemento - http://www.pokermemento.com/ |
Posted By: Oleg
Date 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.
------------- Oleg, Support Team CODEJOCK SOFTWARE SOLUTIONS |