asked on

inheritance problem and access to protected members in derived class

What would be a reason that a derived class doesn't seem to have direct access to the protected members in a parent class unless prefacing it with the namespace?

ie:

class a
{
public:
a()
{
m_pList = new CPtrList();
}

virtual ~a();

protected:
CPtrList* m_pList;
};

#include "a.h"
class b : public a
{
public test()
{
CFoo oFoo = new CFoo();
m_pList->AddTail(oFoo); // this line fails as m_pList = 0xcccccccc

a::m_pList->AddTail(oFoo); // this works
}
}

am I declaring something wrong?

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VolatileVoid

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PMH4514

ASKER

oh yeah, duh!

PMH4514

ASKER

>>so your ctor needs to allocate memory for m_pList

or call the parent class constructor, which allocates the memory

Axter

Hi PMH4514,
> >class b : public a
> >{
> > public test()
> > {
> > CFoo oFoo = new CFoo();
> > m_pList->AddTail(oFoo); // this line fails as m_pList = 0xcccccccc
> >
> > a::m_pList->AddTail(oFoo); // this works
> > }
> >}

Try add : to the end of public, adn you need a return type for test.

David Maisonave :-)
Cheers!

Axter

VolatileVoid,
> >If I recall correctly, a derived class's constructor doesn't call the
> >parent class constructor, so your ctor needs to allocate memory for m_pList

That's not true.
The default parent contstructor will get called automatically.

David Maisonave :-}

Axter

class b : public a
{
public:
void test()
{
CFoo oFoo = new CFoo();
m_pList->AddTail(oFoo); // this line fails as m_pList = 0xcccccccc

a::m_pList->AddTail(oFoo); // this works
}
};

Try the above code. It should work via both methods.
The reason it might have failed with original code, is becuase the compiler is getting confuse since there is no return type for the function.

Axter

VolatileVoid,
> >a derived class's constructor doesn't call the parent class constructor

FYI:
IAW C++ standard, a derived class constructor can not be called without first calling the parent constructor.

David Maisonave :-}