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problem on saving in mfc with Serialize(CArchive &ar)

Posted on 2001-06-18
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867 Views
Last Modified: 2013-11-20
I created a base object called CBaseObject and it goes roughly like this:

class CBaseObject : public CObject  
{
     DECLARE_SERIAL(CBaseObject)

public:
     void Serialize(CArchive &ar);
     ...
     ...

}

The Serialize function is:
void CBaseObject::Serialize(CArchive &ar)
{
     CObject::Serialize(ar);
}

Then I created another class:

class CObjDoor : public CBaseObject  
{
public:
     void Serialize(CArchive &ar);
     ...
     ...

}

Which serialize function is:

void CObjDoor::Serialize(CArchive &ar)
{
     CBaseObject::Serialize(ar);
     if (ar.IsStoring())
          ar << nID << ptCenterPoint << fAngle << 
                 fFrameDepth << fFrameWidth << fTotalWidth << 
                fDoorThickness << fDoorOpenAngle << bFlipH << bFlipV;
     else
          ar >> nID >> ptCenterPoint >> fAngle >> 
                 fFrameDepth >> fFrameWidth >> fTotalWidth >> 
                fDoorThickness >> fDoorOpenAngle >> bFlipH >> bFlipV;
}

The class is used to store the door position, width, thickness, etc... but the problem is it doesnt save anything, when I open the file there is no doors...

It works fine with Wall Class that I previously created... it is directly inherit CObject as its base class.. so I guess the problem with the door is the inheritance?? pleaseee help meee....
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Question by:techpage
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9 Comments
 
LVL 3

Expert Comment

by:_mb_
ID: 6202866
Do you call these macro: IMPLEMENT_SERIAL (CObjDoor, CBaseObject, 1) ?
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 6203416
Hi techpage,

you'll need to declare 'Serial' as virtual at least in the base class, i.e.:

class CBaseObject : public CObject  
{
 DECLARE_SERIAL(CBaseObject)

 public:
  virtual void Serialize(CArchive &ar);
...
};

hope that helps,

ZOPPO
0
 
LVL 1

Expert Comment

by:nivel
ID: 6203501
virtual is good practice in cases like this, but as long as you don't do

ar << ((CBaseObject)obj);
instead of
ar << ((CObjDoor)obj);
it should work.

The IMPLEMENT_SERIAL, must be there though.
DECLARE_SERIAL(CObjDoor) is usually placed inside the class declaration, and IMPLEMENT_SERIAL(CObjDoor, CBaseObject, 1) in the definition file.
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 6203565
well, I think if techpage would have forgotton one of these macros they compiler would
create a lot of errors...

Further, code like
ar << ((CBaseObject)obj);
won't be compiled at all until techpage implements an operator << and operator >> for use with CArchive...

so, he'll have to use something like CArchive::ReadObj() or CArchive::WriteObj() which get's as argument
a 'const CObject*', so calling this for CBaseObject* will call CBaseObject::Serialize(), but calling it with
a CObjDoor* will also call CBaseObject::Serialize(), since all classes derived from CBaseObject don't
have virtual Serialize() function implemented...

further, techpage, you should make sure to call base class's Serialize() function before serializing
the derived class...

ZOPPO
0
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LVL 3

Author Comment

by:techpage
ID: 6204989
when I write:

IMPLEMENT_SERIAL(CObjDoor,CBaseObject,1)

the compiler showed error message:

error C2512: 'CObjDoor' : no appropriate default constructor available

what does that mean?
0
 
LVL 3

Author Comment

by:techpage
ID: 6204994
do you think that serialize can't work with a derived class?? it works okay with a class derived from CObject.

CBaseObject : CObject
CObjDoor : CBaseObject

so what's wrong with that... I guess it should work fine... but it's not !! why???
0
 
LVL 9

Accepted Solution

by:
Pacman earned 100 total points
ID: 6205167
> error C2512: 'CObjDoor' : no appropriate default constructor available

that means that your class "CObjDoor" has no default constructor. Add it to your class:

  CObjDoor();

I'm wondering how you could compile the code without using the IMPLEMENT_SERIAL() ...
0
 
LVL 9

Expert Comment

by:Pacman
ID: 6205177
> you'll need to declare 'Serial' as virtual at least in the base class, i.e.:

Serialize is already virtual (in CObject).
Repeating the word "virtual" is good programming practice but doesn't change anything.
0
 

Expert Comment

by:tridot
ID: 7539979
IMPLEMENT_SERIAL(CWord,CObject,1)

error C2512: 'CArchive' : no appropriate default constructor available

It have default constructor "CWord();"
but
Why tell me 'CArchive' no appropriate default constructor available,what meanings?
0

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