How to fix an External: ACCESS VIOLATION error in Pascal? - pascal

Question

I'm getting an error in Pascal, and according to my research it's due to a declaration error (class or variable). It has to be something small, since it was working just fine. I would really appreciate any help.
To be more specific, the error I'm getting is:
'External:ACCESS VIOLATION' with message: Accedd violation reading from address $000004A8. In line 66: Efa.Text:=D.Fa ;
unit UnidadProyectoInformaticaUno;
{$mode objfpc}{$H+}{$R+}{$Q+}
interface
uses
Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls,Math;
type
{ TForm1 }
TForm1 = class(TForm)
BNext: TButton;
BPrev: TButton;
BAdd: TButton;
BDel: TButton;
BClose: TButton;
EFa: TEdit;
EIm: TEdit;
EOch: TEdit;
EOt: TEdit;
ENum: TEdit;
LabFa: TLabel;
LabIm: TLabel;
LabOch: TLabel;
LabOt: TLabel;
LabNUM: TLabel;
procedure BAddClick(Sender: TObject);
procedure BCloseClick(Sender: TObject);
procedure BDelClick(Sender: TObject);
procedure BNextClick(Sender: TObject);
procedure BPrevClick(Sender: TObject);
private
public
end;
var
Form1: TForm1;
implementation
{$R *.lfm}
type
R= record
Fa,Im,Och: string[20];
Ot:array[1..5] of integer;
end;
Var F:file of R;
D,D1,D2:R;
Irec,i,j,k:integer;
note,grade,nada:string;
procedure OutRec;
begin
with Form1 do
IF Irec > 0 then
begin
seek(F,Irec-1);
read(F,D);
EFa.Text:=D.Fa;
EIm.Text:=D.Im;
for i:= 1 to 5 do
begin
grade:= grade +IntToStr(D.Ot[i])+' ';
end;
Eot.Text:=grade;
EOch.Text:=D.Och;
Enum.Text:= IntToStr(Irec);
end
else
begin
EFa.Text:=nada;
Enum.Text:=nada;
end;
end;
{ TForm1 }
procedure TForm1.BNextClick(Sender: TObject);
begin
If Irec = filesize(F) then
Exit
else
Irec:= Irec+1;
OutRec;
end;
procedure TForm1.BAddClick(Sender: TObject);
begin
D.Fa:=Efa.Text;
D.Im:=Eim.Text;
D.Och:=EOch.Text;
Note:= Eot.text;
for i:= 1 to 5 do
begin
k:=Pos(' ',Note);
D.Ot[i]:= strToInt(Copy(Note,1,k-1));
Delete(Note,1,k);
end;
seek(F,FileSize(F));
Write(F,D);
Irec:= FileSize(F);
OutRec;
end;
procedure TForm1.BCloseClick(Sender: TObject);
begin
close
end;
procedure TForm1.BDelClick(Sender: TObject);
begin
for i:= Irec+1 to Filesize(F) do
begin
seek(F,i-1);
read(F,D);
Seek(F,i-2);
Write(F,D);
end;
Seek(F,Filesize(f)-1);
Truncate(F);
Irec:= Min(Irec,FileSIze(F));
Outrec;
end;
procedure TForm1.BPrevClick(Sender: TObject);
begin
if Irec<2 then Exit;
Irec:= Irec-1;
OutRec;
end;
function Sort(Z:R):string;
begin
Result:=Z.Fa+' '+Z.Im+' '+Z.Och;
end;
procedure BStatus;
begin
with Form1 do
BNext.Enabled:= Irec < FileSize(f);
end;
procedure B1Status;
begin
with Form1 do
BPrev.Enabled:= Irec > 1;
end;
procedure B2Status;
begin
with Form1 do
BAdd.Enabled:= length(Eot.Text) > 0 ;
end;
procedure B3Status;
begin
with Form1 do
BDel.Enabled:= IRec > 0;
end;
begin
assignfile(F,'file.dat');
try reset(F);
except
rewrite(F);
end;
Irec:= Min(1,filesize(F));
OutRec;
for i :=1 to filesize(F)-1 do
for j:= Filesize(F) to i do
begin
seek(F,i);
read(F,D1,D2);
if Sort(D1)>Sort(D2) then
begin
write(f,D2,D1);
end;
end;
end.

Answer 1

In Free Pascal Reference guide, version 3.04 (May 2018), Paragraph 16.2 that deals with Units, it is said that a unit may have an initialization part and a finalization part. It is also said: "An initialization section by itself (i.e. without finalization) may simply be replaced by a statement block.", which is what you have in your code.
That statement block, between the begin and end of the unit, executes at program initialization before the Form1 (declared in the same unit) is created. Therefore you can not refer to anything belonging to the form, like fields, controls, methods, etc. in this statement block, neither directly nor indirectly.
You are calling procedure OutRec, which refers to Efa: TEdit of the form. Since the form is not yet created, you get the error of Access violation.
You must rearrange your code so it doesn't attempt to access any parts of the form from the statement block that replaces a unit initialization part.