Reference for C++ Virtual Pointer.
Questions tagged [vptr]
94 questions
2
votes
2 answers
Virtual table pointers
I decided to find out how vtable is built realy.So I opened debugger and found out some weird thing. The node ptr contains a few vptr. I always thought that there was only one vptr per object. Could anybody explain to me what's going on here ? (I…
Oleksii Hamov
- 156
- 7
2
votes
2 answers
In C++, can we upcast an array and then try to put another subtype into it (inspired by Java ArrayStoreException)?
I have tried to see what would happen in C++ if we try to "break" an array of objects in a similar way we can try to do it in Java.
In Java we can have an array of type Double[], for example, upcast it to Number[] (because Double is a subclass of…
Sergey Gankin
- 23
- 3
1
vote
5 answers
reference variables and inheritence
The following code:
#include
class Parent
{
public:
virtual void func() {printf("Parent\n");}
};
class Child1 : public Parent
{
virtual void func() {printf("Child1\n");}
};
class Child2 : public Parent
{
virtual void func()…
OSH
- 2,847
- 3
- 25
- 46
1
vote
2 answers
How does Base class pointer access the member variable (vptr) of Derived class?
Lets consider the following example
#include
class Base {
public:
virtual void foo() {
std::cout << "Base::foo()" << std::endl;
}
};
class Derived : public Base {
public:
void foo() override {
std::cout <<…
H Kumar
- 37
- 6
1
vote
2 answers
Virtual Table and Object Slicing
In object slicing, when a derived class object is copied to a Base class object, does the _vptr of Derived class also get copied to _vptr of Base class, like other members of class Base? If not, why?
class Base {
public :
virtual void Display()…
Suraj Kottayi
- 56
- 5
1
vote
1 answer
c++ vtable in multiple inheritance, pointer to thunk method
I read this article:
https://shaharmike.com/cpp/vtable-part2/
And I can not understand why in the vtable (at the end of article) we have this pointer:
0x400918 0x400820 non-virtual thunk to Child::FatherFoo()
but not pointer directly to method…
Łukasz Ciałoń
- 11
- 1
1
vote
1 answer
How to find VPTR in C++ assembly code?
class Base {
public:
Base() {}
virtual void Get() { }
};
class Derivered : public Base {
public:
virtual void Get() { }
};
int main() {
Base* base = new Derivered();
base->Get();
return 0;
}
I use gcc 5.4.0 to compile the code, and…
Pengcheng
- 439
- 1
- 4
- 14
1
vote
3 answers
why do we even need VPTR?
And why don't we use the same method for non virtual functions?
I mean, why do we use virtual functions in that way? Can't we just use them as non-virtaul ones and override them?
And if this method is saving us time/space or what ever, why don't we…
GMan
- 81
- 7
1
vote
1 answer
Could not call virtual member function after read object from file
Problem:
I wrote an object into a file in binary mode using std::fstream. However, when I read it back from that file to another object and then call one of the virtual member functions of this new object, there's a memory access violation error.…
Stoatman
- 758
- 3
- 9
- 22
1
vote
4 answers
memcpy derived class to base class, why still called base class function
I am reading Inside the C++ Object Model. In section 1.3
So, then, why is it that, given
Bear b;
ZooAnimal za = b;
// ZooAnimal::rotate() invoked
za.rotate();
the instance of rotate() invoked is the ZooAnimal instance and not that of Bear?…
Divlaker
- 401
- 6
- 16
1
vote
3 answers
where is the overridden virtual method saved in the vtable c++ in multiple inheritance
In C++, there is no class representation at run-time but I can always call an overridden virtual method in the derived class. where is that overridden method saved in the vtable? here's a piece of code to demonstrate:
struct B1 {
virtual void f() {…
Loay
- 483
- 3
- 18
1
vote
3 answers
Virtual functions mechanism implementation
first:
I read somewhere that the mechanism of virtual functions is undefined. i.e. that mean that every compiler can impelement it differently. But, every text that I found about virtual function mechanisn talk about VTBL and VPTR.
Is there another…
asaf app
- 384
- 2
- 3
- 12
1
vote
3 answers
Size of C++ object increases as I add more interfaces... does Java do this?
I'm doing a little experiment to try to mimic java's interfaces in C++.
I have a class "Derived" inheriting from base class "Base" and also two interfaces. I notice that with each interface I inherit from, the size of my Derived class goes up,…
Verdagon
- 2,456
- 3
- 22
- 36
1
vote
3 answers
size of derived class in virtual inheritance
#include "stdafx.h"
#include
using namespace std;
class ClassA
{
protected:
int width, height;
public:
void set_values(int x, int y)
{
width = x;
height = y;
}
};
class ClassB :…
nagaradderKantesh
- 1,672
- 4
- 18
- 30
0
votes
2 answers
When operator delete() in assembly deletes vptr pointer?
The vptr is deleted when operator delete() is called.
But the vptr pointer is hidden, and we don't have to care about its memory structure (plus each compiler has a different system on how it works.)
I'd like to know when exactly the vptr in an…
Dean Seo
- 5,486
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