C / C++ / MFC

class A{
public :
A(){};
virtual ~A(){};
virtual void do()=0;
};

class B : public A
{
public:
  B() {}
  virtual ~B() {}
  virtual void do() { std::cout << "In B::do\n"; }
}

void Blah(A* pA) { pA->do(); }

void main()
{
  B* pB=new B();//No error
  Blah(pB);
}

Stuart Dootson wrote:

Full stop. No argument

hINTModuleState wrote:

OK I know that "instantiating an abstract class" is moral issue

hINTModuleState wrote:

Just posting the question before I'll go and see the source code of a C++ compiler, in the aim that may be there is an answer

hINTModuleState wrote:

I need to know why

Stuart Dootson wrote:

It's because you have undefined method pointers in the classes vtable

hINTModuleState wrote:

do we know how and when the compiler checks that vtable ?

hINTModuleState wrote:

I'll go and see the source code of a C++ compiler

class A
{
public :
	A(){}
	~A(){}
	virtual void do() = 0;
};

void main()
{
	A* pA = (A*)malloc(sizeof(A));
	pA->A::A();
}

«_Superman_» wrote:

void main(){ A* pA = (A*)malloc(sizeof(A)); pA->A::A();}

ThatsAlok ou can’t allocate memory for Class through C malloc, because it just allocate the memory, but will not do any class object initialisation task like call for constructor/destructor

class A
{
public :
	A(){myName=_T("outlaw class"}
	~A(){}
	virtual void do() = 0;
        CString myName;
        void concreteMember(){AfxMessageBox(myName);}
};

void main()
{
	A* pA = (A*)malloc(sizeof(A));
	pA->A::A();
        //
        pA->concreteMember();
}

#include <stdlib.h>
#include <stdio.h>

class Base
{
public:
   virtual void do_it2()  { printf("Base::do_it2\n"); }
};

class A : public Base
{
public :
   A(){}
   ~A(){}
   virtual void do_it() = 0;
   virtual void do_it2()  { printf("A::do_it2\n"); }
   int a;
};

void aa(Base* pBase)
{
   pBase->do_it2();
}

void main()
{
   A* pA = (A*)malloc(sizeof(A));
   pA->A::A();
   aa(pA);
   pA->do_it();
}