Self reference in Template class?

[nw]

Hi comp.lang.c++,

I have the following header (simple.h):

#ifndef SIMPLE
#define SIMPLE

template<class _prec=double>
class Simple {

public:

Simple() {
}

Simple<_prec> next;
};

#endif

and c++ file:

#include <iostream>
#include "simple.h"

using namespace std;

int main() {
Simple<double> s;
}


Compilation gives me the error:

simple.h: In instantiation of 'Simple<double>':
simple.cpp:7: instantiated from here
simple.h:12: error: 'Simple<_prec>::next' has incomplete type
simple.h:5: error: declaration of 'class Simple<double>'

under g++ 4.1.2. I guess I need to add a prototype for Simple, but I
can't quite see how to do this for a template class. Any help
appreciated!

 

[Fei Liu]

Hi comp.lang.c++,

I have the following header (simple.h):

#ifndef SIMPLE
#define SIMPLE

template<class _prec=double>
class Simple {

public:

Simple() {
}

Simple<_prec> next;
};

#endif

and c++ file:

#include <iostream>
#include "simple.h"

using namespace std;

int main() {
Simple<double> s;
}


Compilation gives me the error:

simple.h: In instantiation of 'Simple<double>':
simple.cpp:7: instantiated from here
simple.h:12: error: 'Simple<_prec>::next' has incomplete type
simple.h:5: error: declaration of 'class Simple<double>'

under g++ 4.1.2. I guess I need to add a prototype for Simple, but I
can't quite see how to do this for a template class. Any help
appreciated!

You cannot do this. Declare next as a pointer or reference type (and
make sure the pointee is always valid of course during runtime).

Fei

 

[Puppet_Sock]

Hi comp.lang.c++,

I have the following header (simple.h):

#ifndef SIMPLE
#define SIMPLE

template<class _prec=double>
class Simple {

public:

  Simple() {
  }

  Simple<_prec> next;

};

#endif

[snip]

Um. Is that going to work?

You make an object of type Simple<x>. It has a data member
of type Simple<x>. That data member has a data member of
type Simple<x>. And so on. Eventually the two little girls
from "The Shining" come out and ask you to come play with
them "forever and ever and ever."

Possibly you want a pointer as data member?
Socks

 

[nw]

of type Simple<x>. That data member has a data member of
type Simple<x>. And so on. Eventually the two little girls
from "The Shining" come out and ask you to come play with
them "forever and ever and ever."

Possibly you want a pointer as data member?

uh yea, I didn't think this though.

Definitely don't want to invoke room 237, will refactor.