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reference to pointer used in ctor - using 'this' in ctor (repost- corrected sample code)

P: n/a
template<class T>
class A
{
public:
A() {
T * object = new T(this); //passing instance as parent of nested class
m_obj.push_back(object);
}

~A() {
for (std::vector<T>::iterator it= m_obj.begin();
it != m_obj.end(); it++) delete *it ;
}

private:
std::vector<T*m_objs ;
};

class B
{
public:
friend class A;
~B(){};

private:
B(A<B>* parent):m_parent(parent){}

A<B>* m_parent ;
};
class C
{
public:
friend class A;
~C(){};

private:
C(A<C>*& parent):m_parent(parent){}

A<C>* m_parent ;
};
int main( int argc, char* argv[])
{
A<Bab ; // Ok
A<Cac ; // Croaks here ...
};
Class A instantiated with B compiles ok, but when instantiated with
class C (that accepts a *&), I get the error message - cannot convert
parameter 1 from A const* to A* - why is that ?

Why is a reference to a ptr being passed as a const ptr ?

If 'this' is a const ptr during construction (I doubt this assertion
very much), then why is it ok to use as a non-const pointer in class B?

Aug 28 '07 #1
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2 Replies


P: n/a
Anonymous wrote:
[..]
The code still doesn't compile because of numerous errors (like 'm_obj'
and 'm_objs', declarations of friends that are templates, etc. Read
the FAQ 5.8 please.
class C
{
public:
friend class A;
~C(){};

private:
C(A<C>*& parent):m_parent(parent){}
The advice is still the same:

C(A<C>* const& parent)...
>
A<C>* m_parent ;
};
int main( int argc, char* argv[])
{
A<Bab ; // Ok
A<Cac ; // Croaks here ...
};
Class A instantiated with B compiles ok, but when instantiated with
class C (that accepts a *&), I get the error message - cannot convert
parameter 1 from A const* to A* - why is that ?

Why is a reference to a ptr being passed as a const ptr ?

If 'this' is a const ptr during construction (I doubt this assertion
very much), then why is it ok to use as a non-const pointer in class
B?
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
Aug 28 '07 #2

P: n/a
Anonymous wrote:
template<class T>
class A
{
public:
A() {
T * object = new T(this); //passing instance as parent of nested class
m_obj.push_back(object);
}

~A() {
for (std::vector<T>::iterator it= m_obj.begin();
it != m_obj.end(); it++) delete *it ;
}

private:
std::vector<T*m_objs ;
};

class B
{
public:
friend class A;
~B(){};

private:
B(A<B>* parent):m_parent(parent){}

A<B>* m_parent ;
};
class C
{
public:
friend class A;
~C(){};

private:
C(A<C>*& parent):m_parent(parent){}

A<C>* m_parent ;
};
int main( int argc, char* argv[])
{
A<Bab ; // Ok
A<Cac ; // Croaks here ...
};
Class A instantiated with B compiles ok, but when instantiated with
class C (that accepts a *&), I get the error message - cannot convert
parameter 1 from A const* to A* - why is that ?

Why is a reference to a ptr being passed as a const ptr ?

If 'this' is a const ptr during construction (I doubt this assertion
very much), then why is it ok to use as a non-const pointer in class B?
I attempted to compile your code, but found the template class friend
problem, as Victor marked else-thread.
You inject a friend A into B, actually A is a template class, so you
have to write A<Tas a friend of B(so B have also to be templated),

template <class T>
class B
{
public:
friend class A<T>;
....

when come to declaration of A's object,
A<Bab;
B have to be changed into B<X>, where X is recursively dependent on T of
A<T>, which is to be a templated B.
So the recursive declaration looks like this:
A<B<B<B.... >

So the job couldn't be done. Probably you have to redesign your classes.

--
Thanks
Barry
Aug 29 '07 #3

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