$DEFINE: how does it work?

[alogrep 0]

HI

I hope someone can shed some light. I can mke it to work

I have this code (pseudo)

FUNCTION DOTHERPORT;
BEGIN
{$ifDEF  BO}
          result :=DoCharges(true,-1,false,False,false,lg('CLOSE CHARGES'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$else}

         result := DoCharges(sender=Nil,-1,False,False,FALSE,lg(TDsFancyButton(Sender).Caption),'',0,dm2.sysdate.fieldbyname('date').asdatetime);
{$endif}
END;

function selectreport(sender: Tobject);
begin
  if sender = good1 then
{$DEFINE BO}
   dotherport;
   
end;

FUNCTION DOTHERPORT;
BEGIN
{$ifDEF  BO}
          result :=DoCharges(true,-1,false,False,false,lg('CLOSE CHARGES'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$else}

         result := DoCharges(sender=Nil,-1,False,False,FALSE,lg(TDsFancyButton(Sender).Caption),'',0,dm2.sysdate.fieldbyname('date').asdatetime);
{$endif}
END;

function selectreport(sender: Tobject);
begin
  if sender = good1 then
{$DEFINE BO}
  else
{$define OLD}
   dotherport;
   
end;

I would expect that the line under {$ifdef BO

  would execute. 

Instead it goes to the other line.

How does $DEFINE work?

Thanks.

[Darian Miller 386]

• {$DEFINE BO} is a compiler directive for conditional compilation:  https://docwiki.embarcadero.com/RADStudio/en/Conditional_compilation_(Delphi)

• Once the program is compiled, all {$IFDEF ...} logic is set and does not change at runtime.

[Remy Lebeau 1618]

Pascal code is compiled top-down in a single pass. DEFINE, IFDEF, etc are compiler directives that are evaluated only at compile-time. The resulting code is fixed, it cannot be changed at runtime. If you try to IFDEF something before it has been DEFINE'd, the result will be False. Hence the name IF-DEFined.

 

In any case, DEFINE/IFDEF is not the correct solution for your problem anyway. You are making a decision based on data known only at runtime, so you need to add an extra parameter to your function that is called at runtime (you need to add a Sender parameter, too), eg:

function doTheReport(Sender: TObject; Bo: Boolean);
begin
  if Bo then
    Result := DoCharges(true, -1, False, False, False, lg('CLOSE CHARGES'), '1', dm2.SysDate.FieldByName('date').AsDateTime)
  else
    Result := DoCharges(Sender=nil, -1, False, False, False, lg(TDsFancyButton(Sender).Caption), '', 0, dm2.SysDate.FieldByName('date').AsDateTime);
end;

function selectReport(Sender: TObject);
begin
  doTheReport(Sender, Sender = good1);
end;

Alternatively:

function doTheReport(Sender: TObject);
begin
  if Sender = good1 then
    Result := DoCharges(true, -1, False, False, False, lg('CLOSE CHARGES'), '1', dm2.SysDate.FieldByName('date').AsDateTime)
  else
    Result := DoCharges(Sender=nil, -1, False, False, False, lg(TDsFancyButton(Sender).Caption), '', 0, dm2.SysDate.FieldByName('date').AsDateTime);
end;

function selectReport(Sender: TObject);
begin
  doTheReport(Sender);
end;

 

Edited yesterday at 02:51 AM by Remy Lebeau

[Rollo62 589]

As explained above, define work top-down as compiletime, pretty much as the "defines" in C/C++.

This is very useful since you can switch between certain code behaviour parts, include or not to compile, depending on a compiletime defined condition.
 

//Can be used with DEFINED() in a more speaking, checkbox-like version
{$DEFINE ___USE_THE_BO_VARIANT }
{$DEFINE _X_USE_THE_MO_VARIANT }
{$DEFINE ___USE_THE_ZO_VARIANT }

FUNCTION DOTHERPORT;
BEGIN
{$ifDEF  _X_USE_THE_BO_VARIANT}
          result :=DoCharges(true,-1,false,False,false,lg('CLOSE CHARGES'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$else}

         result := DoCharges(sender=Nil,-1,False,False,FALSE,lg(TDsFancyButton(Sender).Caption),'',0,dm2.sysdate.fieldbyname('date').asdatetime);
{$endif}
END;

//Or maybe in mode complex scenarios, as switch/case-like option, like this
FUNCTION DOTHERPORT2;
BEGIN

{$if     DEFINED( _X_USE_THE_BO_VARIANT ) }
          result :=DoCharges(true,-1,false,False,false,lg('CLOSE CHARGES'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$elseif DEFINED( _X_USE_THE_MO_VARIANT ) }
         result := DoCharges(sender=Nil,-1,False,False,FALSE,lg(TDsFancyButton(Sender).Caption),'',0,dm2.sysdate.fieldbyname('date').asdatetime);
{$elseif DEFINED( _X_USE_THE_ZO_VARIANT ) }
          result :=DoCharges(true,-1,false,False,false,lg('ZOOOO'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$else                                    }
          result :=DoCharges(true,-1,false,False,false,lg('NOTHING ELSE MATTERS'),'1',dm2.sysdate.fieldbyname('date').asdatetime)
{$endif}

END;

 

Edited yesterday at 05:39 AM by Rollo62