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How to use the SendMessageTimeOut function ?

Posted on 1998-11-25
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Last Modified: 2010-04-04
Hello !
In my code I make modifications in the registry.
After those modifications I have to notify all others applications of those changes by broadcasting the WM_WININICHANGE message.
Under win95 I have to use the SendMessageTimeOut function.
The SDK give this example :
SendMessageTimeOut(HWND_BROADCAST,WM_WININICHANGE,0,0L,(LPARAM)(LPCTSTR)"windows",SMTO_NORMAL,1000,NULL);
But it doesn't work !
Does anybody know how to use this function ?
If you have some examples, it will be great !
Thanks in advance.
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Question by:nk51
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by:Madshi
Comment Utility
Hmmm. I don't think, you can use SendMessage or SendMessageTimeout to send broadcast messages. Don't know why it stands in the SDK.
Please try to use "PostMessage(HWND_BROADCAST,WM_WININICHANGE,...)".

Regards, Madshi.
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by:Madshi
Comment Utility
P.S: Try

(1) PostMessage(HWND_BROADCAST,WM_SETTINGCHANGE,0,lparam(pointer('Windows')));
or
(2) PostMessage(HWND_BROADCAST,WM_SETTINGCHANGE,0,0);

WM_WININICHANGE is obsolete.
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Author Comment

by:nk51
Comment Utility
if I use :
PostMessage(HWND_BROADCAST,WM_SETTINGCHANGE,0,lparam(pointer('Windows')));
the compilation return the message :
"incorrect cast"
if I use :
PostMessage(HWND_BROADCAST,WM_SETTINGCHANGE,0,0);
the compilation is OK but it doesn't work :
all others applications aren't notify about the changes I made in the registry.
Have you an explication about the compilation error ?
thanks.
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by:Madshi
Comment Utility
nk51,

I looked again at the documentation. I'm sorry. The SDK is right. I was wrong...   :-(
Now here comes the working solution:

procedure TForm1.Button1Click(Sender: TObject);
var s1 : string;
    c1 : cardinal;
begin
  s1:='windows';
  SendMessageTimeout(HWND_BROADCAST,WM_SETTINGCHANGE,0,integer(pointer(s1)),SMTO_NORMAL,1000,c1);
end;

Regards, Madshi.

P.S: This works with Delphi4. If you have Delphi3 or lower, perhaps you have to change "c1: cardinal" to "c1: integer".
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Author Comment

by:nk51
Comment Utility
You're answer seems to be good but the SendMessageTimeout function erase the modification I made in the registry and restore the previous value.
Have you an idea about what's happening ?

My code :

procedure TForm1.Button3Click(Sender: TObject);
var s1 : string;
    c1 : integer;
begin
   //Modification de la registry
   Imprimante := TStringList.Create;
   RegImprimante := TRegistry.Create;
   RegImprimante.RootKey := HKEY_LOCAL_MACHINE;
   if RegImprimante.OpenKey('Config\0001\System\CurrentControlSet\Control\Print\Printers',False)
   then
   begin
      RegImprimante.WriteString('Default','Tertiaire');
      RegImprimante.LazyWrite := False;
      RegImprimante.CloseKey;
   end;
   RegImprimante.free;

   s1:='windows';
   SendMessageTimeout(HWND_BROADCAST,WM_WININICHANGE,0,integer(pointer(s1)),SMTO_NORMAL,1000,c1);

end;
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Accepted Solution

by:
Madshi earned 50 total points
Comment Utility
Try

WritePrivateProfileString('windows','device','Tertiaire,driver,LPT1:','win.ini');

This seems to be one of the cases where the win.ini settings dominate the registry settings...

Regards, Madshi.
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Author Comment

by:nk51
Comment Utility
Your answer is excellent.
But to use the WritePrivateProfileString function, I need to know the driver and the port of the printer I want to put as default.
So I use the GetPrivateProfileString function to retrieve those parameters. But I have a problem of Access violation because of the PChar I use. Have you an idea about this problem ?

Thanks.

My code :

function TForm1.PrinterParams : string;
var
   buffer : pChar;
begin

    GetPrivateProfileString('devices','Tertiaire','',buffer,sizeof(buffer),'win.ini');
    result := buffer;

end;
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Expert Comment

by:Madshi
Comment Utility
Your "buffer" is only a pointer to a non-defined memory address. So what happens is: Windows writes 4 bytes (sizeOf(pointer)=4) to a non-defined memory address.
You can either allocate (and then of course free) a pchar using GetMem/FreeMem.
Or you can use "my" method:

begin
  SetLength(result,MAX_PATH);
  GetPrivateProfileString('devices','Tertiaire','',pchar(result),MAX_PATH,'win.ini');
  result:=string(pchar(result));  // This line shortens the string by looking at the #0 char...
end;

Regards, Madshi.
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by:nk51
Comment Utility
Thank, you're great Madshi !
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Expert Comment

by:Madshi
Comment Utility
No problem...  :-)
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