Mega Code Archive
Trapping errors
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These two code examples shows a program that performs an integer-division
of two numbers.
There's at least two possible ways to get an error out from these examples:
1. To put in a non-digit.
2. To divide by zero.
These errors are trapped and output in nice customized messages.
{*****************************************************************
* Unit Name: Unit1
* Purpose : An example that shows how to trap errors in an
* application, and how to give these errors
* customized messages.
* (It's nicer not to run this appl. from Delphi. Run
* it directly from the exe-file.)
*
* Author : Mats Asplund, 2001-02-20
****************************************************************}
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TForm1 = class(TForm)
Edit1: TEdit;
Button1: TButton;
Edit2: TEdit;
Edit3: TEdit;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
const
// The errormessages that should show up, when error occurs.
Error1 = 'Only digits: 0-9 are allowed !';
Error2 = 'Division by Zero. Try again !';
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
var E: Exception;
begin
try
// Do the division
Edit3.Text := IntToStr(StrToInt(Edit1.Text) div StrToInt(Edit2.Text));
except
on E: Exception do
begin
// Look for 2 types of Error.
// Show a message-dialog if it's one of them.
if Pos('not a valid integer', E.Message) > 0 then
MessageDlg(Error1, mtError, [mbOK], 0);
if Pos('Division by zero', E.Message) > 0 then
MessageDlg(Error2, mtError, [mbOK], 0);
end;
end;
end;
end.
{*****************************************************************
* Unit Name: Unit2
* Purpose : This example uses already-made exception classes.
* Otherwise it will do just the same as the example above.
* (It's nicer not to run this appl. from Delphi. Run
* it directly from the exe-file.)
*
* Author : Mats Asplund, 2001-02-22
****************************************************************}
unit Unit2;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TForm1 = class(TForm)
Edit1: TEdit;
Button1: TButton;
Edit2: TEdit;
Edit3: TEdit;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
const
// The errormessages that should appeare, when error occurs.
Error1 = 'Only digits: 0-9 are allowed !';
Error2 = 'Division by Zero. Try again !';
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
try
Edit3.Text:= IntToStr(StrToInt(Edit1.Text) div StrToInt(Edit2.Text));
except
on EConvertError do
MessageDlg(Error1, mtError, [mbOK], 0);
on EDivByZero do
MessageDlg(Error2, mtError, [mbOK], 0);
end;
end;
end.
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