[Q] Template: Undefined Constructors

[Eric]

Ok, this is very strange.

in TRegionGrower.h , I've got:

--
template <class T>
class TRegionGrower
{
public:

TRegionGrower( void );
~TRegionGrower( void );
};
--

In TRegionGrower.c p, I've got:

--
#include "TRegionGrower. h"

template <class T>
TRegionGrower<T >::
TRegionGrower( void )
{

}



template <class T>
TRegionGrower<T >::
~TRegionGrower( void )
{

}
--

I use this class by doing:

TRegionGrower<U Int8> regionGrower;

I get two link errors telling me that the constructor and destructor are
undefined.

However, if I remove the constructor and destructors from the .cp file
and change the .h file to:

--
template <class T>
class TRegionGrower
{
public:

TRegionGrower( void )
{
}

~TRegionGrower( void )
{
}
};
--

The link errors go away.

Any idea what might be going on here?

[Russell Hanneken]

Re: [Q] Template: Undefined Constructors

Eric wrote:[color=blue]
>
> I get two link errors telling me that the constructor and destructor are
> undefined.
>
> However, if I remove the constructor and destructors from the .cp file
> and change the .h file to:
>
> template <class T>
> class TRegionGrower
> {
> public:
>
> TRegionGrower( void )
> {
> }
>
> ~TRegionGrower( void )
> {
> }
> };
>
> The link errors go away.[/color]

The FAQ addresses this issue:

http://www.parashift.com/c++-faq-lite/containers-and-templates.html#faq-34.12

--
Russell Hanneken
rghanneken@pobo x.com
Remove the 'g' from my address to send me mail.

[Claudio Jolowicz]

Re: [Q] Template: Undefined Constructors

On Mon, 19 Apr 2004, Eric wrote:
[color=blue]
>Ok, this is very strange.
>
>in TRegionGrower.h , I've got:
>
>--
>template <class T>
>class TRegionGrower
>{
>public:
>
> TRegionGrower( void );
> ~TRegionGrower( void );
>};
>--
>
>In TRegionGrower.c p, I've got:
>
>--
>#include "TRegionGrower. h"
>
>template <class T>
>TRegionGrower< T>::
>TRegionGrowe r( void )
>{
>
>}
>
>
>
>template <class T>
>TRegionGrower< T>::
>~TRegionGrower ( void )
>{
>
>}
>--
>
>I use this class by doing:
>
> TRegionGrower<U Int8> regionGrower;
>
>I get two link errors telling me that the constructor and destructor are
>undefined.
>[/color]

1. How about giving us the definition of UInt8? With a sensible typedef,
there shouldn't be any errors. If its a macro, anything is possible.

2. Is the last line of code in a separate source file or in
TRegionGrower.c p?

3. What does the command line to (compile and) link the files look like?

[color=blue]
>However, if I remove the constructor and destructors from the .cp file
>and change the .h file to:
>
>--
>template <class T>
>class TRegionGrower
>{
>public:
>
> TRegionGrower( void )
> {
> }
>
> ~TRegionGrower( void )
> {
> }
>};
>--
>
>The link errors go away.
>
>Any idea what might be going on here?
>
>
>[/color]

--
Claudio Jolowicz

[Michiel Salters]

Re: [Q] Template: Undefined Constructors

egusenet@verizo n.net (Eric) wrote in message news:<1gci5k9.1 7r0locvblnj0N%e gusenet@verizon .net>...[color=blue]
> Ok, this is very strange.
>
> in TRegionGrower.h , I've got:
>
> --
> template <class T>
> class TRegionGrower
> {
> public:
>
> TRegionGrower( void );
> ~TRegionGrower( void );
> };
> --
>
> In TRegionGrower.c p, I've got:[/color]
[ the obvious implementation ]

The FAQ reference in the previous post is correct, although there
currently is an alternative solution. These templates need extra
bookkeeping, as the FAQ explains. This is enabled using the export
keyword on the class, but it is today only supported on the Comeau
compiler.

Regards,
Michiel Salters