Question

I am wondering if it is possible to call a derived class´ function from within a function called by the base constructor (shouldn´t it already be created when the code in the brackets are executed?)

#pragma once
class ClassA
{
public:
 ClassA(void);
 virtual ~ClassA(void);

 void Init();

protected:
 short m_a;
 short m_b;

 virtual void SetNumbers(short s);
};

include "ClassA.h"
#include <iostream>


ClassA::ClassA(void) : m_a(0), m_b(0)
{
Init();
}


ClassA::~ClassA(void)
{
}

void ClassA::SetNumbers(short s)
{
 std::cout << "In ClassA::SetNumbers()\n";
 m_a = s;
 m_b = s;
}

void ClassA::Init()
{
 this->SetNumbers(2);
}

---

#pragma once
#include "ClassA.h"
class ClassB : public ClassA
{
public:
 ClassB(void);
 virtual ~ClassB(void);

 virtual void SetNumbers(short);

 int x;
};

#include "ClassB.h"
#include <iostream>


ClassB::ClassB(void)
{
}


ClassB::~ClassB(void)
{
}

void ClassB::SetNumbers(short s)
{
 std::cout << "In ClassB::SetNumbers()\n";

 m_a = ++s;
 m_b = s;

 ClassA::SetNumbers(s);
}

Any suggestions how to do it?…

Thank You in advance :)…

Answer 1

No. All parts of B (starting with A, as it’s base) are constructed before B’s constructor is called. So, by the time SetNumbers is called, no part of B (except for the A part) has been constructed — and that may include the v-table, so there’s no way to know where that call is going to go.

Of course, there is a simple solution to this: Call B::SetNumber() from within B’s constructor (That is, after all, the purpose of B’s constructor)