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dialogs

Posted on 1998-10-22
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Last Modified: 2010-04-16
I have written this program in Borland TPW 1.5, and i keep getting application errors. please help, the file is stock.res is available by emailing me(i don't think you can upload files).

program Stock_exchange;

{$R STOCK.res}

uses WinTypes, WinProcs, WObjects, wincrt;

type
  PTestDialog = ^TTestDialog;
  TTestDialog = object(TDialog)
    procedure butt(var Msg: TMessage); virtual id_First + 159 ;  
   end;

type
  PMyWindow=^TMyWindow;
  TMyWindow=object(TWindow)
    constructor Init(AParent: PWindowsObject; Atitle: PChar);
    procedure players(var msg:tmessage); virtual cm_first + 51;
  end;    
     
  TMyApplication = object(TApplication)
    procedure InitMainWindow;virtual;    
  end;
   
var MyApp:TMyApplication;          
 
constructor TMyWindow.Init(AParent: PWindowsObject; Atitle: PChar);
begin  
  TWindow.Init(AParent, Atitle);
  attr.menu :=loadmenu(hinstance, pchar(100));
end;

procedure ttestdialog.butt(var msg: tmessage);
var TextItem: PChar;
begin
 getdlgitemtext(getdlgitem(hwindow,151),151,textitem,20);
 
end;

procedure TMyWindow.Players(var Msg: tmessage);
begin
     Application^.ExecDialog(New(PTestDialog, Init(@Self, 'DIALOG_1')));
end;

procedure TMyApplication.InitMainWindow;
begin
  MainWindow:=New(PMyWindow, Init(nil,'Menus'));
end;

begin
   myapp.init('Video');
   myapp.run;
   myapp.done;
end.
 
please help!

Please use POBWEST@YAHOO.COM (as i can't read mail from the stated one in the profile for the next week)
0
Comment
Question by:pobwest
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3 Comments
 
LVL 2

Expert Comment

by:joe_h
ID: 1215841
Mail me the complete code, I'll have a look :)

joe@hw.cz

0
 
LVL 2

Accepted Solution

by:
joe_h earned 100 total points
ID: 1215842
Problem is

   procedure ttestdialog.butt(var msg: tmessage);
    var TextItem: PChar;  {<-------- HERE.}
    begin
     getdlgitemtext(getdlgitem(hwindow,151),151,textitem,20);
    end;    

The thing is, that by saying 'var textitem:PChar' you declare a pointer, which, at this moment, POINTS SOMEWHERE, BUT NOBODY KNOWS WHERE. So, a call to getdlgitemtext will result in up to 20 bytes (the last parameter) being changed somewhere in memory, causing Windows to crash - you have never actually allocated space for the resulting string.

I guess you meant to write something like:
   procedure ttestdialog.butt(var msg: tmessage);
    var TextItem: array[0..20] of char;
    begin
     getdlgitemtext(getdlgitem(hwindow,151),151,@textitem,20);
    end;

Here, ther 'var' statement actually allocates 21 bytes (I like to put an extra byte in for safety) for the string, while the @textitem returns a pointer to this allocated space.

HTH, Joe
 
0
 

Author Comment

by:pobwest
ID: 1215843
That the one!

I changed the procedure to this

procedure ttestdialog.butt(var msg: tmessage);
var TextItem:array[0..20] of char;
a:integer;
begin
   getdlgitemtext(hwindow,201,textitem,20);
   writeln('Returned Value :',a);
   writeln('Text recived   :',textitem);
end;

and it seems to have done the trick


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