Access violation at address 0045D810 in module 'Project1.exe'

[johanzold]

Hello,

i try to test the well known ping.pas / icmp.pas, without any luck

---

This the first few lines of the head of the Unit1:

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, StdCtrls, Ping;

type
TForm1 = class(TForm)

If i Write here :
Ping1:Tping;

then later i call: Ping1.Timeout := 3000;

I get the following error message: Exceptional class EAccessViolation with message Access violation at address 0045D810 in module 'Project1.exe'. Read of address 00000030.

If save and close the project, and open it again I get the following error message:

Field Form1.Ping1 does not have a corresponing component. Remove the declatation ?
---

If I move Ping1:Tping; to the 'var' part:

var
Form1: TForm1;
Ping1:Tping;

I get the following error message: Exceptional class EAccessViolation with message Access violation at address 0045CB98 in module 'Project1.exe'. Read of address 00000030.

---

If I add Ping1: Tping to Unit1.dfm:

object Form1: TForm1
Ping1= TPing

I get the first erro I had described.

---------

My question is: what am i doing wrong ?

 

[whosrdaddy]

Hi,

your trying to access an object that's not created yet, hence the AV. the ping variable is nothing more than a pointer to a structure (the TPing object) in memory.

If save and close the project, and open it again I get the following error message:

Field Form1.Ping1 does not have a corresponing component. Remove the declatation ?

add the ping : TPing line in the public section of the form object (look for the keyword public), or, as you did declare it as a global variable.

then you must do something like this

....
 Ping := TPing.Create; // this will create your actual object
 // now you can reference the object
 Ping.Timeout := 3000;
 DoSomethingWithPing;
 // now free the allocated memory 
 FreeAndNil(Ping);
 // object is now destroyed
 Ping.Timeout := 3000; // ---> this will create an AV since the object no longer exists

...

I hope this makes sense....

Cheers,
Daddy

-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!

 

[johanzold]

Thank you! The ' Ping := TPing.Create; ' version works fine. Unfortunately I compline the program, it needs additional 10 second to complile it, but it is okay.

The first version (ping1 : TPing; in the public part)
unfortunately still don't work.

1.
type
TForm1 = class(TForm)
r1: TMemo;
public
ping1 : TPing;
procedure FormShow(Sender: TObject);


It will gives an error message: Error reading Form1.OnShow: Invalid property value

2.

type
TForm1 = class(TForm)
r1: TMemo;
procedure FormShow(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
ping1 : TPing;
end;


This version still creates an error message :
Exceptional class EAccessViolation with message Access violation at address 0045CB98 in module 'Project1.exe'. Read of address 00000030

Any idea where is the problem ?

 

[johanzold]

The original Pingtst1.pas made by F. Piette also starts like these:


unit PingTst1;

{$I ICSDEFS.INC}

interface

uses
Windows, Messages, SysUtils, Classes, Forms, StdCtrls, Controls, Ping;

const
PingTestVersion = 103;
CopyRight : String = ' PingTest (c) 1997-2005 Francois Piette V1.03 ';

type
TPingTstForm = class(TForm)
Ping1: TPing;


So


type
SomeForm = class(TForm)
Ping1: TPing;


should work somehow. But how ?

 

[whosrdaddy]

oh I see.

in fact the TPing object is a component.
any reference direct under the class definition is put there by the designer. did you install FPiette's ICS component suite?

if this is the case you just drop a TPing component from the palette onto your form. in that case the TPing.Create is handled by the TForm.

/Daddy

-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!