Problem with Inheritance

[Gama Franco]

Hi,

I've been developing this API, but now I get stuck in a compiling error
and I'm out of ideas. Some comments are welcome.

The hierarchy is bases in three classes, and I will explain it bellow in
detail.

The three classes are:
1 - IFolderManager -> abstract base class
2 - FolderManagerCo mmon : public IFolderManager
3 - FolderManager : public FolderManagerCo mmon

The properties of this relation are:

1 - IFolderManager has only abstract methods and no attributes.

2 - IFolderManagerC ommon implements a small set of methods from the base
class.
3 - IFolderManagerC ommon declares and implements some protected methods,
and as some private attributes.
4 - IFolderManagerC ommon has no constructors, since it is also an
abstract class (doesn't implement all the methods from the base class).

5 - FolderManager implements all the methods from the base class that
are not implemented by FolderManagerCo mmon.

6 - All the three classes have virtual destructors.
7 - All methods are virtual.
8 - Only FolderManager has constructors.

From this description we see that the union of FolderManagerCo mmon and
FolderManager implement all the methods declared by the interface (base
class).

The problem is that when I compile the code I get the following error:
.../src/common/FolderManagerCo mmon.h:7: error: candidates are:
FolderManagerCo mmon::FolderMan agerCommon(cons t FolderManagerCo mmon&)

This error points to the constructor of FolderManager, in
FolderManager.c xx. And I have no ideia of what is going on.

I've tried to explain to resume the error, so that there was no need to
look at the code. But I will place the code here also, in case I
couldn't explain myself:
--------------------------------------------------------------
IFolderManager. h
--------------------------------------------------------------
#ifndef IFOLDERMANAGER_ H
#define IFOLDERMANAGER_ H
#include "ITableManager. h"
#include <vector>
#include <string>
using namespace std;

/** @interface
* @stereotype base_class */
class IFolderManager {

public:
virtual IFolderManager* createFolder(co nst string& folderName,
const string& folderAttribute s,
const string& folderDescripti on) const
throw (TIDB_Exception ) =0;

virtual ITableManager* createTable(con st string& tableName,
ICondDBTable& table,
const string& tableAttributes ,
const string& tableDescriptio n) const
throw(TIDB_Exce ption)=0;

virtual void deleteFolder(co nst string& folderName) const
throw (TIDB_Exception ) = 0;

virtual void deleteTable(con st string& tableName) const
throw (TIDB_Exception ) = 0;

virtual IFolderManager* getFolderManage r(const string& folderName)
const
throw(TIDB_Exce ption)= 0;

virtual vector < IFolderManager >* getFolderManage rs() const
throw(TIDB_Exce ption) = 0;

virtual ITableManager* getTableManager (const string& tableName) const
throw(TIDB_Exce ption) = 0;

virtual vector < ITableManager >* getTableManager s() const
throw(TIDB_Exce ption)= 0;

virtual const string& getDescription( ) const =0;

virtual const string& getPath() const =0;

virtual const string& getVersion() const=0;

virtual ~IFolderManager () {} //dummy destructor
};
#endif //IFOLDERMANAGER_ H
--------------------------------------------------------------
IFolderManagerC ommon.h
--------------------------------------------------------------
#ifndef FOLDERMANAGERCO MMON_H
#define FOLDERMANAGERCO MMON_H

#include "IFolderManager .h"
#include "../common/IDatabase.h"

class FolderManagerCo mmon : public IFolderManager {
public:
virtual const string& getDescription( ) const;

virtual const string& getPath() const;

virtual const string& getVersion() const;

virtual ~FolderManagerC ommon();

protected:
virtual const IDatabase& getDatabase() const;

private:
string path;
string version;
string description;
IDatabase& database;
};

#endif // FOLDERCOMMON_H
--------------------------------------------------------------
FolderManager.h
--------------------------------------------------------------
#ifndef FOLDERMANAGER_H
#define FOLDERMANAGER_H
#include "../common/FolderManagerCo mmon.h"

/**
* @stereotype Oracle
*/
class FolderManager : public FolderManagerCo mmon {

public:
FolderManager(c onst string& path, const IDatabase& database);

virtual IFolderManager* createFolder(co nst string& folderName,
const string& folderAttribute s,
const string& folderDescripti on) const
throw (TIDB_Exception );

virtual ITableManager* createTable(con st string& tableName,
ICondDBTable& table,
const string& tableAttributes ,
const string& tableDescriptio n) const
throw (TIDB_Exception );

virtual void deleteFolder(co nst string& folderName) const
throw (TIDB_Exception );

virtual void deleteTable(con st string& tableName) const
throw (TIDB_Exception );

virtual IFolderManager* getFolderManage r(const string& folderName)
const
throw (TIDB_Exception );

virtual vector < IFolderManager >* getFolderManage rs() const
throw (TIDB_Exception );

virtual ITableManager* getTableManager (const string& tableName) const
throw (TIDB_Exception );

virtual vector < ITableManager >* getTableManager s() const
throw (TIDB_Exception );

virtual ~FolderManager( );

private:

/** @link dependency */
/*# P_Folder lnkFolder; */

/** @link dependency */
/*# P_Table lnkTable; */
};
#endif //FOLDERMANAGER_H

[Gianni Mariani]

Gama Franco wrote:
....

The problem is that when I compile the code I get the following error:
../src/common/FolderManagerCo mmon.h:7: error: candidates are:
FolderManagerCo mmon::FolderMan agerCommon(cons t FolderManagerCo mmon&)

This error points to the constructor of FolderManager, in
FolderManager.c xx. And I have no ideia of what is going on.
It seems you have missed putting FolderManager.c xx in your code snippet.
I have not been able to reproduce the error you describe with the code
you have posted.

Please post a complete, compileable snippet of code that demonstrates
the problem you describe.

Anyhow, you do mention "error points to the constructor of
FolderManager". FolderManager has no declared constructor so it's using
the default constructor generated by the compiler. It seems you are
defining a new one in the .cxx file which is probably an error.

I've tried to explain to resume the error, so that there was no need to
look at the code. But I will place the code here also, in case I
couldn't explain myself:

.... the code below, which does not have any errors under gcc 3.4, was
taken from your original post.

#include <vector>
#include <string>
using namespace std;

struct TIDB_Exception {};
struct ITableManager {};
struct ICondDBTable {};
struct IDatabase {};

/** @interface
* @stereotype base_class */
class IFolderManager {

public:
virtual IFolderManager* createFolder(co nst string& folderName,
const string& folderAttribute s,
const string& folderDescripti on) const
throw (TIDB_Exception ) =0;

virtual ITableManager* createTable(con st string& tableName,
ICondDBTable& table,
const string& tableAttributes ,
const string& tableDescriptio n) const
throw(TIDB_Exce ption)=0;

virtual void deleteFolder(co nst string& folderName) const
throw (TIDB_Exception ) = 0;

virtual void deleteTable(con st string& tableName) const
throw (TIDB_Exception ) = 0;

virtual IFolderManager* getFolderManage r(const string& folderName)
const
throw(TIDB_Exce ption)= 0;

virtual vector < IFolderManager >* getFolderManage rs() const
throw(TIDB_Exce ption) = 0;

virtual ITableManager* getTableManager (const string& tableName) const
throw(TIDB_Exce ption) = 0;

virtual vector < ITableManager >* getTableManager s() const
throw(TIDB_Exce ption)= 0;

virtual const string& getDescription( ) const =0;

virtual const string& getPath() const =0;

virtual const string& getVersion() const=0;

virtual ~IFolderManager () {} //dummy destructor
};
class FolderManagerCo mmon : public IFolderManager {
public:
virtual const string& getDescription( ) const;

virtual const string& getPath() const;

virtual const string& getVersion() const;

virtual ~FolderManagerC ommon();

protected:
virtual const IDatabase& getDatabase() const;

private:
string path;
string version;
string description;
IDatabase& database;
};

/**
* @stereotype Oracle
*/
class FolderManager : public FolderManagerCo mmon {

public:
FolderManager(c onst string& path, const IDatabase& database);

virtual IFolderManager* createFolder(co nst string& folderName,
const string& folderAttribute s,
const string& folderDescripti on) const
throw (TIDB_Exception );

virtual ITableManager* createTable(con st string& tableName,
ICondDBTable& table,
const string& tableAttributes ,
const string& tableDescriptio n) const
throw (TIDB_Exception );

virtual void deleteFolder(co nst string& folderName) const
throw (TIDB_Exception );

virtual void deleteTable(con st string& tableName) const
throw (TIDB_Exception );

virtual IFolderManager* getFolderManage r(const string& folderName)
const
throw (TIDB_Exception );

virtual vector < IFolderManager >* getFolderManage rs() const
throw (TIDB_Exception );

virtual ITableManager* getTableManager (const string& tableName) const
throw (TIDB_Exception );

virtual vector < ITableManager >* getTableManager s() const
throw (TIDB_Exception );

virtual ~FolderManager( );

private:

/** @link dependency */
/*# P_Folder lnkFolder; */

/** @link dependency */
/*# P_Table lnkTable; */
};

[David Hilsee]

"Gama Franco" <ti***@cern.c h> wrote in message
news:41******** **************@ news.telepac.pt ...

Hi,

I've been developing this API, but now I get stuck in a compiling error
and I'm out of ideas. Some comments are welcome.

The hierarchy is bases in three classes, and I will explain it bellow in
detail.

The three classes are:
1 - IFolderManager -> abstract base class
2 - FolderManagerCo mmon : public IFolderManager
3 - FolderManager : public FolderManagerCo mmon

The properties of this relation are:

1 - IFolderManager has only abstract methods and no attributes.

2 - IFolderManagerC ommon implements a small set of methods from the base
class.
3 - IFolderManagerC ommon declares and implements some protected methods,
and as some private attributes.
4 - IFolderManagerC ommon has no constructors, since it is also an
abstract class (doesn't implement all the methods from the base class).
I just want to point out that abstract classes may need to have
constructors. In fact, in your case, I would expect IFolderManagerC ommon to
have constructors, because it has private data that it must initialize. If
you like, they may be protected, but they should still exist.
5 - FolderManager implements all the methods from the base class that
are not implemented by FolderManagerCo mmon.

6 - All the three classes have virtual destructors.
7 - All methods are virtual.
8 - Only FolderManager has constructors.

From this description we see that the union of FolderManagerCo mmon and
FolderManager implement all the methods declared by the interface (base
class).

The problem is that when I compile the code I get the following error:
../src/common/FolderManagerCo mmon.h:7: error: candidates are:
FolderManagerCo mmon::FolderMan agerCommon(cons t FolderManagerCo mmon&)

This error points to the constructor of FolderManager, in
FolderManager.c xx. And I have no ideia of what is going on.
You didn't provide the source to FolderManager.c xx, and it looks like you
didn't provide all of the compiler's messages. It's difficult to figure out
what the compiler's complaining about if you can't see the relevant
information. Consider posting that information if you aren't getting the
help you need.

<snip> class FolderManagerCo mmon : public IFolderManager {
public:
virtual const string& getDescription( ) const;

virtual const string& getPath() const;

virtual const string& getVersion() const;

virtual ~FolderManagerC ommon();

protected:
virtual const IDatabase& getDatabase() const;

private:
string path;
string version;
string description;
IDatabase& database;
};

<snip>

How do you expect "database" to be initialized? This class needs a
constructor.

--
David Hilsee

[Gama Franco]

Hi,

I'm sorry to post with a different e-mail, but the Newsgroup's Server
of my ISP is not working and I had to use a (very) old google account.

There are some points that I don't understand. Why does an abstract
class need a constructor, and how can an abstract class have a
constructor?
For what I remember, it is not possible to create objects of an
abstract class... or is it?

Also, what is the definition of 'default constructor'? Is the one
without arguments?

The set of classes "Database" use the same technique (one Interface,
one Common and a final class)... the strange is that I don't get a
compiler error for those three classes, but that must happen because
of some detail that I don't know of.
I'm also not sure if the Database classe finish compilation, because
IDatabase 'includes' IFolderManager.
Now I post the compiler errors:

#########The one related to the constructor
.../src/Oracle/FolderManager.c xx: In constructor
`FolderManager: :FolderManager( const std::string&, const IDatabase&)':
.../src/Oracle/FolderManager.c xx:4: error: no matching function for
call to `FolderManagerC ommon::FolderMa nagerCommon()'

#########Relate d to the inheritence IFolderManager <--
FolderManagerCo mmon
.../src/common/FolderManagerCo mmon.h:7: error: candidates are:
FolderManagerCo mmon::FolderMan agerCommon(cons t FolderManagerCo mmon&)

Bellow I will post FolderManagerCo mmon.cxx and FolderManager.c xx

=============== =============== =============== =============== ====
FolderManagerCo mmon.cxx
=============== =============== =============== =============== ====
#include "FolderManagerC ommon.h"

const string& FolderManagerCo mmon::getDescri ption() const{
return this->description;
}

const string& FolderManagerCo mmon::getPath() const{
return this->path;
}

const string& FolderManagerCo mmon::getVersio n() const {
return this->version;
}

FolderManagerCo mmon::~FolderMa nagerCommon()
{
}

//protected methods
const IDatabase& FolderManagerCo mmon::getDataba se() const{
return this->database;
}
=============== =============== =============== =============== ====
FolderManager.c xx
=============== =============== =============== =============== ====
#include "FolderManager. h"

FolderManager:: FolderManager(c onst string& path, const IDatabase&
database)
{
//TODO
}

ITableManager* FolderManager:: getTableManager (const string& tableName)
const
throw (TIDB_Exception )
{
//TODO
return NULL;
}

vector < ITableManager >* FolderManager:: getTableManager s() const
throw (TIDB_Exception )
{
//TODO
return new vector < ITableManager >;
}

ITableManager* FolderManager:: createTable(con st string& tableName,
ICondDBTable& table,
const string& tableAttributes ,
const string& tableDescriptio n) const
throw (TIDB_Exception )
{
//TODO
return NULL;
}

void FolderManager:: deleteTable(con st string& tableName) const
throw (TIDB_Exception )
{
//TODO
}
void FolderManager:: deleteFolder(co nst string& folderName) const
throw (TIDB_Exception )
{
//TODO
}

IFolderManager* FolderManager:: createFolder(
const string& folderName,
const string& folderAttribute s,
const string& folderDescripti on) const
throw (TIDB_Exception )
{
//TODO
return new FolderManager( "/" + folderName, this->getDatabase()) ;
}

IFolderManager* FolderManager:: getFolderManage r(const string&
folderName) const
throw (TIDB_Exception ) {
//TODO
return new FolderManager( "/" + folderName, this->getDatabase()) ;
}

vector < IFolderManager >* FolderManager:: getFolderManage rs() const
throw (TIDB_Exception )
{
//TODO
return new vector<IFolderM anager >;
}

FolderManager:: ~FolderManager( )
{

}

Thanks in advance,
Gama Franco

[Gianni Mariani]

Gama Franco wrote:
....

There are some points that I don't understand. Why does an abstract
class need a constructor, and how can an abstract class have a
constructor?
You can certainly have a constructor for an abstract class. The term
"abstract" class means that the class cannot be instantiated by itself.
For what I remember, it is not possible to create objects of an
abstract class... or is it?
It is if you inherit from it - but not by itself.

Also, what is the definition of 'default constructor'? Is the one
without arguments?
Yes. However, don't be confused by the default constructor provided by
the compiler and the default constructor that may be defined.

....

Now I post the compiler errors:

#########The one related to the constructor
../src/Oracle/FolderManager.c xx: In constructor
`FolderManager: :FolderManager( const std::string&, const IDatabase&)':
../src/Oracle/FolderManager.c xx:4: error: no matching function for
call to `FolderManagerC ommon::FolderMa nagerCommon()'

#########Relate d to the inheritence IFolderManager <--
FolderManagerCo mmon
../src/common/FolderManagerCo mmon.h:7: error: candidates are:
FolderManagerCo mmon::FolderMan agerCommon(cons t FolderManagerCo mmon&)

Bellow I will post FolderManagerCo mmon.cxx and FolderManager.c xx
....

This is your problem. You are defining a constructor which needs (and
will) instantiate the constructor for it's inherited classes (in this
case FolderManagerCo mmon ). In this case it seems like gcc does not
create a default constructor for FolderManagerCo mmon most likely because
you need to initialize FolderManagerCo mmon::database. Since
FolderManagerCo mmon::database is a reference it can only be bound by the
constructor and the compiler has no way of knowing how to do it and
hence it seems like gcc in this case simply does not provide a default
constructor. I'm not sure if this is what the standard requires but I
for one like this behaviour (because it's likely a bug to do anything
else anyway!).

FolderManager:: FolderManager(c onst string& path, const IDatabase&
database)
{
//TODO
}

You need to do somthing like this:
class FolderManagerCo mmon : public IFolderManager {
public:

FolderManagerCo mmon( const IDatabase& database )
: database( database )
{
}
....
const IDatabase& database;
};

FolderManager:: FolderManager(
const string& path, const IDatabase& database
)
: FolderManagerCo mmon( database )
{
//TODO
}
And all will be well.