Why constructor can not be make virtual while destructor can be virtual
2  889  gpraghuram 1,275
Recognized Expert Top Contributor
Virtual comes into picture only after the object gets created.
So we cant have a virtual constructor to create the object.
raghu
Virtual has several meanings in C++ depending on where you find it.
For derived objects that are used in functions expecting base object pointers or refereences, the virtual tells the compiler that if there is a choice between the base class method orthe derived class method, that the derived method is to be used.
For destructors, it tells the compiler that even though I ask you to delete the deirved object by deleting a pointer to the base class, the compiler is to call the deirved class destructor. If the destrcutor is not virtual, when you delete a derived object by deleting it using a base class pointer ot refererence, only the base class part of the object is cleaned up. Any allocations you made in the derived class are not cleaned up and you leak.
For inheritance, a virtual base class tells the compiler that there is to be only one base object inside the derived object.
The problem with virtual for beginners is the assumption that is means the same thing all the time. Part of the problem was the ANS C++ committee refusing new keywords in C++ for new situations. Hence, virtual has three meanings.
Sign in to post your reply or Sign up for a free account.
Similar topics | |
by: santosh |
last post by:
Hello,
I was going through the Marshal Cline's C++ FAQ-Lite.
I have a doubt regarding section 33.10.
Here he is declaring a pure virtual destructor in the base class.
And again defining it inline. Like this.
|
by: ypjofficial |
last post by:
Hello All,
So far I have been reading that in case of a polymorphic class ( having
at least one virtual function in it), the virtual function call get
resolved at run time and during that the vtable pointer is made use
of..
eg.
class one
{
|
by: John Goche |
last post by:
Hello,
page 202 of Symbian OS Explained by Jo Stichbury states
"All virtual functions, public, protected or private, should be
exported"
then page 203 states
"In the rare cases where a pure virtual function body
|
by: desktop |
last post by:
This page:
http://www.eptacom.net/pubblicazioni/pub_eng/mdisp.html
start with the line: "Virtual functions allow polymorphism on a single
argument". What does that exactly mean?
I guess it has nothing to do with making multiple arguments in a
declaration like:
|
by: Jess |
last post by:
Hello,
If I have a class that has virtual but non-pure declarations, like
class A{
virtual void f();
};
Then is A still an abstract class? Do I have to have "virtual void
f() = 0;" instead? I think declaring a function as "=0" is the same
| | |
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, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
|
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, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
|
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
| | |
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
|
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |
