[fpc-pascal] Help with TList example

[James Richters]

Can you please give me an example of the correct way to use new and dispose?

I'll try the pointer

Thanks for the advice

James

-----Original Message-----
From: fpc-pascal <fpc-pascal-bounces at lists.freepascal.org> On Behalf Of Tony Whyman via fpc-pascal
Sent: Tuesday, September 8, 2020 7:21 AM
To: fpc-pascal at lists.freepascal.org
Cc: Tony Whyman <tony.whyman at mccallumwhyman.com>
Subject: Re: [fpc-pascal] Help with TList example

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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