Iam writing an application that uses an abstract base class and a
derived class that is implementation of the abstract base class. Say I
have this piece of code:
Derived *ptrToDerived=NULL;
Base *ptrToBase=NULL;
ptrToDerived= new Derived;
ptrToBase=ptrToDerived;
.....................
.....................
//Do stuff..........
.....................
delete ptrToBase;
Now my doubt is: will the memory be deleted properly. Or what will be
the behaviour of delete in this case, because delete first calls the
destructor of the class, and I have no destructor in the base class. 7 1946
"Rohit" <ro*********@yahoo.com> wrote in message
news:11*********************@z14g2000cwz.googlegro ups.com... Iam writing an application that uses an abstract base class and a derived class that is implementation of the abstract base class. Say I have this piece of code:
Derived *ptrToDerived=NULL; Base *ptrToBase=NULL; ptrToDerived= new Derived; ptrToBase=ptrToDerived; .................... .................... //Do stuff.......... .................... delete ptrToBase;
Now my doubt is: will the memory be deleted properly. Or what will be the behaviour of delete in this case, because delete first calls the destructor of the class, and I have no destructor in the base class.
For delete to work correctly (i.e. not cause Undefined Behavior),
class Base must have a virtual destructor.
Either:
virtual ~Base() = 0; // abstract virtual, not implemented
Or:
virtual ~Base() {} // implemented inline or not, as you prefer
With that, you'll have the guarantee that the memory is properly
released, and that the appropriate (subclass) destructor is called.
Ivan
-- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
"Rohit" <ro*********@yahoo.com> wrote in message
news:11*********************@z14g2000cwz.googlegro ups.com... Iam writing an application that uses an abstract base class and a derived class that is implementation of the abstract base class. Say I have this piece of code:
Derived *ptrToDerived=NULL; Base *ptrToBase=NULL; ptrToDerived= new Derived; ptrToBase=ptrToDerived; .................... .................... //Do stuff.......... .................... delete ptrToBase;
Now my doubt is: will the memory be deleted properly. Or what will be the behaviour of delete in this case, because delete first calls the destructor of the class, and I have no destructor in the base class. http://www.parashift.com/c++-faq-lit....html#faq-20.5
Regards,
Sumit.
--
Sumit Rajan <su*********@gmail.com>
Ivan Vecerina wrote: For delete to work correctly (i.e. not cause Undefined Behavior), class Base must have a virtual destructor. Either: virtual ~Base() = 0; // abstract virtual, not implemented
The destructor has to be implemented. It's called from the derived
class's destructor.
--
Pete Becker
Dinkumware, Ltd. ( http://www.dinkumware.com)
"Pete Becker" <pe********@acm.org> wrote in message
news:6s********************@rcn.net... Ivan Vecerina wrote: For delete to work correctly (i.e. not cause Undefined Behavior), class Base must have a virtual destructor. Either: virtual ~Base() = 0; // abstract virtual, not implemented
The destructor has to be implemented. It's called from the derived class's destructor.
Woops, that's right.
The weird thing (part of what confused my memories) is that an *abstract*
virtual desctructor cannot be defined inline within the class body:
virtual ~Base() = 0 {} //illegal syntax
Thanks,
Ivan
-- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Ivan Vecerina wrote: [...] The weird thing (part of what confused my memories) is that an *abstract*
The term is *pure*. "Abstract" is the term describing the class.
virtual desctructor cannot be defined inline within the class body: virtual ~Base() = 0 {} //illegal syntax
No function can. A function declared pure can an implementation, but only
defined outside the class definition.
V
"Rohit" <ro*********@yahoo.com> wrote in message news:<11*********************@z14g2000cwz.googlegr oups.com>... Iam writing an application that uses an abstract base class and a derived class that is implementation of the abstract base class. Say I have this piece of code:
Derived *ptrToDerived=NULL; Base *ptrToBase=NULL; ptrToDerived= new Derived; ptrToBase=ptrToDerived; .................... .................... //Do stuff.......... .................... delete ptrToBase;
Now my doubt is: will the memory be deleted properly. Or what will be the behaviour of delete in this case, because delete first calls the destructor of the class, and I have no destructor in the base class.
delete is find. BUT delete[] can cause undefind behaviour.
Derived *ptrToDerived=NULL;
Base *ptrToBase=NULL;
ptrToDerived = new Derived[20];
ptrToBase=ptrToDerived;
......
.....
.....
delete[] ptrToBase;
regards, This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
by: Min |
last post by:
CFool
{
public:
void StartWorldWarIII() { /*** Launch Nuclear Missiles **/ }
};
int main()
{
CFool* pFool = new CFool();
delete pFool;
|
by: Abhijeet |
last post by:
I was just toying around idea of deleting this from a member function.
Was expecting that any acess to member variable or function after
deleting sould give me dump(segmetation violation).Cause now...
|
by: Aguilar, James |
last post by:
Hey guys. A new question:
I want to use an STL libarary to hold a bunch of objects I create.
Actually, it will hold references to the objects, but that's beside the
point, for the most part. ...
|
by: Manisha |
last post by:
Hi,
I am creating a C++ dll which is used to process data passed to it
through one of its exported functions. It should be able to process
160 simultaneous requests. For this reason, I have...
|
by: schizoid_man |
last post by:
Hi,
I have the following code snippets and I get a std::bad_alloc error
where I think there should be none. I've attached the relevant bits of
the base class, derived class and the .cpp file...
|
by: NAdir |
last post by:
Hi, thank you for your help.
My VB.Net application contains a document that the user can refresh at any
time.
The refresh works fine and needs to loop through few datatables (hundreds of
rows)....
|
by: happyvalley |
last post by:
Hi,
basically, the test function get a char pointer, and assigned a string
to it. then the string is passed back by the call-by-reference
mechanism. in test(), I reallocate some memory for the...
|
by: Pat |
last post by:
Hi all,
I have a really awkward situation that is causing memory leak problems.
I'm passing data to a driver, and unfortunately, the driver code is not
something I can change, and it is written...
|
by: mc |
last post by:
Hi Experts,
This may be obvious but I can't find anything one way or another. We have
a class which is always allocated using new, e.g. Foo* foo = new Foo() so we
came up with the idea of...
|
by: taylorcarr |
last post by:
A Canon printer is a smart device known for being advanced, efficient, and reliable. It is designed for home, office, and hybrid workspace use and can also be used for a variety of purposes. However,...
|
by: Charles Arthur |
last post by:
How do i turn on java script on a villaon, callus and itel keypad mobile phone
|
by: aa123db |
last post by:
Variable and constants
Use var or let for variables and const fror constants.
Var foo ='bar';
Let foo ='bar';const baz ='bar';
Functions
function $name$ ($parameters$) {
}
...
|
by: ryjfgjl |
last post by:
If we have dozens or hundreds of excel to import into the database, if we use the excel import function provided by database editors such as navicat, it will be extremely tedious and time-consuming...
|
by: ryjfgjl |
last post by:
In our work, we often receive Excel tables with data in the same format. If we want to analyze these data, it can be difficult to analyze them because the data is spread across multiple Excel files...
|
by: emmanuelkatto |
last post by:
Hi All, I am Emmanuel katto from Uganda. I want to ask what challenges you've faced while migrating a website to cloud.
Please let me know.
Thanks!
Emmanuel
|
by: nemocccc |
last post by:
hello, everyone, I want to develop a software for my android phone for daily needs, any suggestions?
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However,...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers,...
| |