[fpc-pascal] Checking if a TStringList already exists

[James Richters]

I don’t seem to have FreeThenNil  I’m using FPC 3.0.4RC1 I don’t use Lazarus.. maybe it’s a Lazarus thing… or maybe it’s in a different unit 

 

plotdraw.pax.pas(20,7) Error: Identifier not found "FreeThenNil"              

 

James

 

From: fpc-pascal <fpc-pascal-bounces at lists.freepascal.org> On Behalf Of Giuliano Colla
Sent: Monday, May 20, 2019 6:01 PM
To: fpc-pascal at lists.freepascal.org
Subject: Re: [fpc-pascal] Checking if a TStringList already exists

 

Il 20/05/2019 15:23, James Richters ha scritto:

Thank you very much for the explanation and examples of this!   I am glad you pointed out the FreeAndNill() function, I will defiantly be needing that.
 
James


Then you might also appreciate the function Assigned. Assigned(P) returns true if P is non-nil, and false if P is Nil. Nothing fancy, just making the code more readable.

>From fpc documentation:



Program Example96;
 
{ Program to demonstrate the Assigned function. }
 
Var P : Pointer;
 
begin
  If Not Assigned(P) then
    Writeln ('Pointer is initially NIL');
  P:=@P;
  If Not Assigned(P) then
    Writeln('Internal inconsistency')
  else
    Writeln('All is well in FPC')
end.

Giuliano

P.S. In some rare case when dealing with complex objects you might need FreeThenNil() in place of FreeAndNil(). Give a look to https://lists.lazarus-ide.org/pipermail/lazarus/2011-April/062743.html



-- 
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