Re: [fpc-pascal] Help with TList example

[Tony Whyman via fpc-pascal]

Two observations:

1. In Pascal you should use "new" and "dispose" to allocate and 
deallocate record types - not GetMem and FreeMem.

2. MyRec is a pointer type and you should code the line as

MyRec^.Value := tmp


On 08/09/2020 12:10, James Richters via fpc-pascal wrote:
I'm trying to figure out how TList works.  I found the code example below by 
doing a search, but I can't compile it,  I get Error: Illegal qualifier on the 
line
     MyRec.Value := tmp;
   It's indicating the error is on the V of Value

I tried commenting that line out, then I get the same error on
     MyRec.AByte := Byte(tmp);
At the A of AByte

So I commented that out too and then I get the error on

    Writeln('Value: ', MyRecList[tmp].Value, ' AByte: ', MyRecList[tmp].AByte);
At the V on Value after MyRecList[tmp].

I don't know enough about the syntax to figure out what's wrong here.  Does 
anyone have any ideas?  It seems like there is something fundamentally wrong.

I'm trying to make a temporary list of records.  Kind of like a TStringList, 
but instead of a list of strings, a list of my own custom records.  Perhaps 
there is a better way?


program Project1;
{$mode objfpc}{$H+}

uses
   SysUtils, Classes;

type
   PMyRec=^TMyRec;
   TMyRec=record
     Value: Integer;
     AByte: Byte;
   end;

   TMyRecList=class(TList)
   private
     function Get(Index: Integer): PMyRec;
   public
     destructor Destroy; override;
     function Add(Value: PMyRec): Integer;
     property Items[Index: Integer]: PMyRec read Get; default;
   end;

{ TMyRecList }

function TMyRecList.Add(Value: PMyRec): Integer;
begin
   Result := inherited Add(Value);
end;

destructor TMyRecList.Destroy;
var
   i: Integer;
begin
   for i := 0 to Count - 1 do
     FreeMem(Items[i]);
   inherited;
end;

function TMyRecList.Get(Index: Integer): PMyRec;
begin
   Result := PMyRec(inherited Get(Index));
end;

var
   MyRecList: TMyRecList;
   MyRec: pMyRec;
   tmp: Integer;
begin
   MyRecList := TMyRecList.Create;
   for tmp := 0 to 9 do
   begin
     GetMem(MyRec, SizeOf(TMyRec));
     MyRec.Value := tmp;
     MyRec.AByte := Byte(tmp);
     MyRecList.Add(MyRec);
   end;

   for tmp := 0 to MyRecList.Count - 1 do
     Writeln('Value: ', MyRecList[tmp].Value, ' AByte: ', MyRecList[tmp].AByte);
   WriteLn('  Press Enter to free the list');
   ReadLn;
   MyRecList.Free;
end.

James

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