Re: 3 level inheritance heirarchy

From:
"Tadeusz B. Kopec" <tkopec@NOSPAMPLEASElife.pl>
Newsgroups:
comp.lang.c++
Date:
21 Dec 2007 21:40:33 +0100
Message-ID:
<476c24c1$1@news.home.net.pl>
On Fri, 21 Dec 2007 08:44:17 -0800, interec wrote:

On Dec 21, 2:34 am, Sachin <sachinc.bira...@gmail.com> wrote:

On Dec 21, 2:05 pm, inte...@interec.net wrote:

I have trying to set up a three level inheritance heirarchy (see
files test.h/cpp below). When I compile this code using g++, I get
the following errors:

bash-3.00$ g++ test.cpp
test.cpp: In constructor `Lev2::Lev2(int, int, int)': test.cpp:33:
error: no matching function for call to `Lev0::Lev0(const void**)'
test.h:27: note: candidates are: Lev0::Lev0(const Lev0&) test.cpp:6:
note: Lev0::Lev0(int)

Can someone please explain whats going on and how I can fix this
problem. Please see code below. If I remove the classes ILev2 and
Lev2 everything compiles fine. Thanks

//-------------------------- FILE: test.h
--------------------------//

#include <iostream>
#include <iomanip>

class ILev0
{
 public:
  virtual ~ILev0() {}
  virtual void PrintLev0() = 0;

};

class ILev1: public virtual ILev0
{
 public:
  virtual ~ILev1() {}
  virtual void PrintLev1() = 0;

};

class ILev2: public virtual ILev1
{
 public:
  virtual ~ILev2() {}
  virtual void PrintLev2() = 0;

};

class Lev0: public virtual ILev0
{
 public:
  Lev0(int nNum);
  virtual void PrintLev0();

 protected:
  int m_nNum0;

};

class Lev1: public virtual Lev0, public virtual ILev1 {
 public:
  Lev1(int nNum0, int nNum1);
  virtual void PrintLev1();
 protected:
  int m_nNum1;

};

class Lev2: public virtual Lev1, public virtual ILev2 {
 public:
  Lev2(int nNum0, int nNum1, int nNum2); virtual void PrintLev2();
 protected:
  int m_nNum2;

};

//-------------------------- FILE: test.cpp
------------------------// #include "test.h"

//-------

Lev0::Lev0(int nNum)
  :m_nNum0(nNum)
{

}

void Lev0::PrintLev0()
{
  std::cout << "Lev0 Num: " << m_nNum0 << std::endl;

}

//-------

Lev1::Lev1(int nNum0, int nNum1)
  :Lev0(nNum0),
   m_nNum1(nNum1)
{

}

void Lev1::PrintLev1()
{
  std::cout << "Lev1 Num: " << m_nNum0 << ", " << m_nNum1 <<
std::endl;

}

//-------

Lev2::Lev2(int nNum0, int nNum1, int nNum2)
  :Lev1(nNum0, nNum1),
   m_nNum2(nNum2)
{

}

void Lev2::PrintLev2()
{
  std::cout << "Lev2 Num: " << m_nNum0 << ", " << m_nNum1 << ", " <<
m_nNum2 << std::endl;

}

//---

main()
{
  Lev0 *b = new Lev0(10);
  b->PrintLev0();

}


//------------------------------------------------------------------//

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Call to Constructor of Lev0 class is missing in the Lev2 constructor.
Resolution is to either implement default constructor in Lev0 class or
make a call to Lev0 constructor in the constructor of Lev2 as follows:
Lev2::Lev2(int nNum0, int nNum1, int nNum2)
  :Lev1(nNum0, nNum1),Lev0(nNum0),
   m_nNum2(nNum2)
{

}


Lev2 constructor explicitly calls Lev1 constructor and Lev1 constructor
explicitly calls Lev0 constructor so why do I need to add a call to Lev0
constructor in Lev2 ?


Because it's a virtual base class.

--
Tadeusz B. Kopec (tkopec@NOSPAMPLEASElife.pl)
Enzymes are things invented by biologists that explain things which
otherwise require harder thinking.
        -- Jerome Lettvin

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