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help on constructor/constructor initialization list with inheritance using templates

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  help on constructor/constructor initialization list with inheritance using templates balaji <kasthurirangan.balaji@gmail.com> - 2011-08-08 02:00 -0700
    Re: help on constructor/constructor initialization list with inheritance using templates jt@toerring.de (Jens Thoms Toerring) - 2011-08-08 09:46 +0000
      Re: help on constructor/constructor initialization list with inheritance using templates balaji <kasthurirangan.balaji@gmail.com> - 2011-08-10 04:01 -0700
        Re: help on constructor/constructor initialization list with inheritance using templates jt@toerring.de (Jens Thoms Toerring) - 2011-08-10 12:06 +0000

#8561 — help on constructor/constructor initialization list with inheritance using templates

Hi,

Pls find below the sample code.

File 1

template< class A, template < typename > class B >
class C : public B<A>
{
  public:
    explicit C(const char *msg);
    ~C();

  private:
    //copy constructor and assignment operator
}

template< class A, template < typename > class B >
C<A, B> :: C(const char *msg)
  : B(msg)
{
}

template< class A, template < typename > class B >
C<A, B> :: ~C()
{
}

File 2

template < class Z>
class B : public Z
{
  public:
    explicit B(const char *msg);
    ~B();

  private:
    //copy constructor and assignment operator
}

template < class Z>
B<Z> :: B(const char *msg)
  : Z(msg)
{
}

template < class Z>
B<Z>::~B()
{
}

File 3

3.h
class A
{
  public:
    explicit A(const char *msg);
    ~A();

  private:
    //copy constructor and assignment operator
}

3.C
#include "3.h"

A::A(const char *msg)
{
}

A::~A()
{
}

main file

#iinclude file 1, file 2 and file 3(.h)

int
main(int argc, char **argv)
{
C<A,B> objc("Success");
return 0;
}

when i compile this code, i get the following error "The base class
"B<A>" cannot be initialized because it does not have a default
constructor.".  I do not understand what i have missed to get this
error. Pls help me to resolve this.

Thanks,
Balaji.

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#8562

balaji <kasthurirangan.balaji@gmail.com> wrote:
> Hi,

> Pls find below the sample code.

> File 1

> template< class A, template < typename > class B >
> class C : public B<A>
> {
>   public:
>     explicit C(const char *msg);
>     ~C();

>   private:
>     //copy constructor and assignment operator
> }

You're missing a semicolon here (and also is some other
places at the end of declarations of classes).

> template< class A, template < typename > class B >
> C<A, B> :: C(const char *msg)
>   : B(msg)

This is the place my compiler doesn't like when other,
minor issues are fixed:

  error: no matching function for call to ‘B<A>::B()’
  note: candidates are: B<Z>::B(const char*) [with Z = A]
  note:                 B<A>::B(const B<A>&)

Shouldn't that be 

template< class A, template < typename > class B >
C< A, B > :: C( const char * msg )
  : B< A >( msg )

since B<A> is the base class C is derived from?

Otherwise I guess the compiler will try to invoke the
default constructor of B<A> (since there's no explicit
call of it - you call B(msg), not B<A>(msg)) and since
there is none it gives up.
                             Regards, Jens
-- 
  \   Jens Thoms Toerring  ___      jt@toerring.de
   \__________________________      http://toerring.de

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#8616

On Aug 8, 2:46 pm, j...@toerring.de (Jens Thoms Toerring) wrote:
> balaji <kasthurirangan.bal...@gmail.com> wrote:
> > Hi,
> > Pls find below the sample code.
> > File 1
> > template< class A, template < typename > class B >
> > class C : public B<A>
> > {
> >   public:
> >     explicit C(const char *msg);
> >     ~C();
> >   private:
> >     //copy constructor and assignment operator
> > }
>
> You're missing a semicolon here (and also is some other
> places at the end of declarations of classes).
>
> > template< class A, template < typename > class B >
> > C<A, B> :: C(const char *msg)
> >   : B(msg)
>
> This is the place my compiler doesn't like when other,
> minor issues are fixed:
>
>   error: no matching function for call to ‘B<A>::B()’
>   note: candidates are: B<Z>::B(const char*) [with Z = A]
>   note:                 B<A>::B(const B<A>&)
>
> Shouldn't that be
>
> template< class A, template < typename > class B >
> C< A, B > :: C( const char * msg )
>   : B< A >( msg )
>
> since B<A> is the base class C is derived from?
>
> Otherwise I guess the compiler will try to invoke the
> default constructor of B<A> (since there's no explicit
> call of it - you call B(msg), not B<A>(msg)) and since
> there is none it gives up.
>                              Regards, Jens
> --
>   \   Jens Thoms Toerring  ___      j...@toerring.de
>    \__________________________      http://toerring.de

Hi Jens,

Thanks for your response and sorry for the late reply as well.

My post wasn't posted atleast for 2 days i believe or atleast i was
unable to see this post.

I too figured out that. What compiler is yours to give the
"candidates". My compiler didn't say that(itx IBM xlC version 7.0).

Thanks,
Balaji.

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#8617

balaji <kasthurirangan.balaji@gmail.com> wrote:
> On Aug 8, 2:46 pm, j...@toerring.de (Jens Thoms Toerring) wrote:
> > balaji <kasthurirangan.bal...@gmail.com> wrote:
> > > template< class A, template < typename > class B >
> > > C<A, B> :: C(const char *msg)
> > >   : B(msg)
> >
> > This is the place my compiler doesn't like when other,
> > minor issues are fixed:
> >
> >   error: no matching function for call to ‘B<A>::B()’
> >   note: candidates are: B<Z>::B(const char*) [with Z = A]
> >   note:                 B<A>::B(const B<A>&)
> >
> > Shouldn't that be
> >
> > template< class A, template < typename > class B >
> > C< A, B > :: C( const char * msg )
> >   : B< A >( msg )
>
> I too figured out that. What compiler is yours to give the
> "candidates". My compiler didn't say that(itx IBM xlC version 7.0).

It's gcc, version 4.4.3. Having the candidates the compiler
considered being shown can be helpful but also, at other times,
a bit annoying when the compiler found hundreds and hundreds
of them and insists on listing each and every one of them;-)

                             Best regards, Jens
-- 
  \   Jens Thoms Toerring  ___      jt@toerring.de
   \__________________________      http://toerring.de

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