template question

[Milan]

I need some help on the following simple program:

//////////////////////////////////////////////
template <class T>
class A
{
public:
T x, y;
A(){x = y = 0;}
A(T x_, T y_):x(x_), y(y_){}
template <class X> A(const A<X> &a){x = a.x; y = a.y; cout << "A" << endl;}
};

class B: public A<int>
{
public:
B(){}
B(int x_, int y_): A<int>(x_, y_){}
template <class X> B(const A<X> &a): A<X>(a){cout << "B" << endl;}
};

class C: public A<double>
{
public:
C(){}
C(double x_, double y_): A<double>(x_, y_){}
template <class X> C(const A<X> &a): A<X>(a){cout << "C" << endl;}
};

int main(int argc, char* argv[])
{
B obj1;
C obj2 = B;
return 0;
}

//////////////////////////////////////////////

It fails to compile on the "C obj2 = B" line. Why?

Thanks for the help.

Regards,
Milan.

[Victor Bazarov]

Re: template question

"Milan" <someone@intern et.com> wrote...[color=blue]
> I need some help on the following simple program:
>
> //////////////////////////////////////////////
> template <class T>
> class A
> {
> public:
> T x, y;
> A(){x = y = 0;}
> A(T x_, T y_):x(x_), y(y_){}
> template <class X> A(const A<X> &a){x = a.x; y = a.y; cout << "A" <<[/color]
endl;}[color=blue]
> };
>
> class B: public A<int>
> {
> public:
> B(){}
> B(int x_, int y_): A<int>(x_, y_){}
> template <class X> B(const A<X> &a): A<X>(a){cout << "B" << endl;}[/color]

You cannot construct A<X> here, it's not a member. You can only
construct A<int>.
[color=blue]
> };
>
> class C: public A<double>
> {
> public:
> C(){}
> C(double x_, double y_): A<double>(x_, y_){}
> template <class X> C(const A<X> &a): A<X>(a){cout << "C" << endl;}[/color]

Same here. You cannot construct A<X>. You can only construct
A<double>.
[color=blue]
> };
>
> int main(int argc, char* argv[])
> {
> B obj1;
> C obj2 = B;[/color]

'B' is a type name. The compiler expects an expression. Did
you mean to write

C obj2 = obj1;

?
[color=blue]
> return 0;
> }
>
> //////////////////////////////////////////////
>
> It fails to compile on the "C obj2 = B" line. Why?[/color]

Doesn't your compiler tell you why? If it doesn't, how do you
know it fails?

Victor

[hrmadhu]

Re: template question

// try
C obj2=obj1
// B is a type...not an object.
// Madhu.


"Milan" <someone@intern et.com> wrote in message news:<bo5t9f$1c 01@imsp212.netv igator.com>...[color=blue]
> I need some help on the following simple program:
>
> //////////////////////////////////////////////
> template <class T>
> class A
> {
> public:
> T x, y;
> A(){x = y = 0;}
> A(T x_, T y_):x(x_), y(y_){}
> template <class X> A(const A<X> &a){x = a.x; y = a.y; cout << "A" << endl;}
> };
>
> class B: public A<int>
> {
> public:
> B(){}
> B(int x_, int y_): A<int>(x_, y_){}
> template <class X> B(const A<X> &a): A<X>(a){cout << "B" << endl;}
> };
>
> class C: public A<double>
> {
> public:
> C(){}
> C(double x_, double y_): A<double>(x_, y_){}
> template <class X> C(const A<X> &a): A<X>(a){cout << "C" << endl;}
> };
>
> int main(int argc, char* argv[])
> {
> B obj1;
> C obj2 = B;
> return 0;
> }
>
> //////////////////////////////////////////////
>
> It fails to compile on the "C obj2 = B" line. Why?
>
> Thanks for the help.
>
> Regards,
> Milan.[/color]

[Milan]

Re: template question

Sorry, I made a mistake. The expression should be

C obj2 = obj1;

However it still fails to compile with an error message "error C2614: 'C' :
illegal member initialization: 'A<int>' is not a base or member". How do I
resolve this? Many thanks.

Regards,
Milan.


"Victor Bazarov" <v.Abazarov@com Acast.net> wrote in message
news:CUvpb.7005 6$mZ5.434158@at tbi_s54...[color=blue]
> "Milan" <someone@intern et.com> wrote...[color=green]
> > int main(int argc, char* argv[])
> > {
> > B obj1;
> > C obj2 = B;[/color]
>
> 'B' is a type name. The compiler expects an expression. Did
> you mean to write
>
> C obj2 = obj1;
>
> ?
>[color=green]
> > return 0;
> > }[/color][/color]

[Victor Bazarov]

Re: template question

"Milan" <someone@intern et.com> wrote...[color=blue]
> Sorry, I made a mistake. The expression should be
>
> C obj2 = obj1;
>
> However it still fails to compile with an error message "error C2614: 'C'[/color]
:[color=blue]
> illegal member initialization: 'A<int>' is not a base or member". How do I
> resolve this? Many thanks.[/color]

By getting a more standard-compliant compiler.

Victor