Initial value of a property in a component

[cdbc]

Hi.

Every Tobject created will have 0, nil null, values assigned to members on creation. (mind you, i might be wrong). Somewhere along, there is a call to fillchar(*,#0) or so or zeromemory(*,*).

Regards Benny

[eny]

Every Tobject created will have 0, nil null, values assigned to members on creation.

Hm, I wonder what the 4th line would do...

Code: Pascal  [Select][+][-]

1. constructor myCustomControl.Create(AOwner: TComponent);  
2. begin  
3.    inherited Create(AOwner);  
4.    FAlpha := 255;      
5. end;

[cdbc]

Hi

Sorry, my point was...:

constructor myCustomControl.Create(AOwner: TComponent);    
begin    
   inherited Create(AOwner); <- in here some zero-memory is going on at creation time.
   FAlpha := 255;        
end;  

[edit]: My bad...

Code: [Select]

      class function TObject.NewInstance : tobject;

        var
           p : pointer;

        begin
           getmem(p, InstanceSize);
           if p <> nil then
              InitInstance(p);
           NewInstance:=TObject(p);
        end;

      class function TObject.InitInstance(instance : pointer) : tobject; {$ifdef SYSTEMINLINE} inline; {$ENDIF}

        begin
           { the size is saved at offset 0 }
           fillchar(instance^, InstanceSize, 0);
           { insert VMT pointer into the new created memory area }
           { (in class methods self contains the VMT!)           }
           ppointer(instance)^:=pointer(self);
           if PVmt(self)^.vIntfTable <> @emptyintf then
             InitInterfacePointers(self,instance);
           InitInstance:=TObject(Instance);
        end;
No zeroing going on at all...
Seems a bit different from delphi...?

Regards Benny

[Laksen]

fillchar(instance^, InstanceSize, 0);

[eny]

No zeroing going on at all...
Seems a bit different from delphi...?

Yep, you're right here, that was one of the Delphi caveats: don't initialize variables before having called the inherited constructor.

[Marc]

No zeroing going on at all...
Seems a bit different from delphi...?

Yep, you're right here, that was one of the Delphi caveats: don't initialize variables before having called the inherited constructor.

??? as laksen wrote, all classes are initialized to zero (opposite to objects)

[eny]

??? as laksen wrote, all classes are initialized to zero (opposite to objects)

I know... and that's a good thing 

I seem to recall that in earlier version of Delphi (version 3, many years ago ) the values of properties were destroyed as soon as an inherited costructor was called, after you had given them a value in the Create constructor. So the statements:

Code: Pascal  [Select][+][-]

1. constructor myCustomControl.Create(AOwner: TComponent);    
2. begin    
3.   FAlpha := 42;        
4.   inherited Create(AOwner);    
5. end;

would still give FAlpha a value of 0.

[cdbc]

Hi

@Laksen: Overlooked that one  May have been a wee bit sleepy...

Regards Benny