Reference for C++ Virtual Pointer.
Questions tagged [vptr]
94 questions
0
votes
0 answers
C++ runtime error invalid vptr when compiling with gcc 8.1 and gcc 8.2
I have a strange runtime error that only happens with GCC 8.2 and GCC 8.1.
When attempting to delete a class with multiple inheritances, the compiler raises a runtime error related to a corrupted virtual pointer.
This minimal example can be found in…
Oshio
- 133
- 4
- 17
0
votes
0 answers
What is the meaning of a pointer to a virtual function?
I have such a piece of code:
struct X
{
virtual void f(){}
virtual void g(){}
virtual void h(){}
};
int main()
{
auto p = &X::f, q = &X::g, r = &X::h;
X *x = new X;
return 0;
}
I thought the pointer to a virtual function…
zclll
- 77
- 7
0
votes
2 answers
does pointer "this" in c++ support virtual mechanism?
Consider that:
class B {
void f() { vf(); };
virtual void vf();
};
class D: public B{
virtual void vf();
};
I thought that in C++ the implementation of B::f() is something like that:
f(B *this) {
*(this->vptr[index])(this);
}
Is…
Solaroi Zeng
- 51
- 5
0
votes
1 answer
C++ How do i get a pointer to a class' virtual function table?
Given:
Example.h
struct Base {
virtual ~Def() = default;
virtual void accept(struct DerivedVisitor* v) = 0;
};
struct Derived : Base {
int num;
void accept(struct DerivedVisitor* v) override;
};
struct DerivedVisitor {
virtual…
Django
- 57
- 6
0
votes
1 answer
Why object with vptr is 12 bytes longer?
#include
class B
{
public:
virtual void f() {std::cout<<"HI";}
int x;
};
class A
{
public:
void f() {std::cout<<"HI";}
int x;
};
int main () {
A a;
B b;
std::cout<
SimpleAsk
- 73
- 5
0
votes
0 answers
Force a specific arrangement of virtual and non virtual base classes
If I have a code like this:
class A {
public:
int data1;
}
class B {
public:
virtual void test() {}
}
class C : public A, public B {
int data2;
}
and when I now create an instance of C its memory layout looks something like…
Panakotta00
- 135
- 9
0
votes
2 answers
Initializing objects with virtual functions on pre-allocated memory without placement new operator - is that possible? If not, why
Let's say there's a simple class hierarchy, and a state object that uses the derived class;
struct base_class {
int Value;
base_class() { this->Value = 1; }
virtual void Func() { printf("Base\n"); };
};
struct derived_class :…
Stas L
- 5
- 4
0
votes
2 answers
are vptr and vtable inherited from base class?
As can be seen, D3 introduces a new virtual function, @function3(), in the middle of the chain of inheritance. I am wondering what is happening with *--vptr and vtable when this happens. D3 is a 'kind of' a new base class now,
class Base {
public:
…
meng
- 3
- 2
0
votes
1 answer
How vptr and vtable works in the bellow virtual related code?
As far i know when we make a function virtual in base class a pointer which can be referred as vptr is created by the compiler and a vtable which holds the entrys of virtual function which are latest version for this class in case of overridden…
user11712295
0
votes
2 answers
Number of vptr created if derived class also has a virtual function which is not present in Base class
class Base
{
public:
virtual void func1()
{
std::cout<<"Base func1"<
Naresh
- 155
- 1
- 9
0
votes
1 answer
placement new with derived class
C++ gurus. Need your help with this little head scratcher:
#include
struct B{
virtual ~B() = default;
virtual void talk() { std::cout << "Be-e-e\n"; }
};
struct D:B{
void talk() override { std::cout << "Duh\n"; }
~D() {…
YePhIcK
- 5,816
- 2
- 27
- 52
0
votes
3 answers
Unexpected virtual function dispatch when using base class reference instead of pointer
Let say I have a simple class hierarchy as follows with a common api:
#include
class Base {
public:
void api() {
foo();
}
protected:
virtual void foo() {
std::cout << "Base" <<…
motam79
- 3,542
- 5
- 34
- 60
0
votes
3 answers
How many entries are in a vtable for an abstract virtual function?
I read that an abstract class can still have a table. But I'm confused on how many entries it would have in its vtable. For example, if my abstract class was:
class Circle(){
virtual void draw() = 0;
}
then how many entries would be in its…
smith1453
- 151
- 1
- 1
- 6
0
votes
1 answer
How virtual inheritance solves Multiple inheritance(Diamond) in c++?Which path will it take?
Below Code is on Diamond problem. virtual inheritance solves this ambiguity.
#include
using namespace std;
class A {
public: void something(){cout<<"A"<
Vijay M M
- 81
- 6
0
votes
2 answers
Object construction and Virtual pointer during mutiple inheritance
class Base1 {
virtual void fun1() { cout << "Base1::fun1()" << endl; }
virtual void func1() { cout << "Base1::func1()" << endl; }
};
class Base2 {
virtual void fun1() { cout << "Base2::fun1()" << endl; }
virtual void func1() {…
anurag86
- 1,635
- 1
- 16
- 31