Odd registry behaviour in WinXP
lazarus / 67-Windows

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CM630 · 2014-10-24 11:43

While fixing a bug in LazSerial I got to synaser. Here is the
problematic code:
Code: [Select]function GetSerialPortNames: string;
var
  reg: TRegistry;
  l, v: TStringList;
  n: integer;
  debvalnames: string;
begin
  l := TStringList.Create;
  v := TStringList.Create;
  reg := TRegistry.Create;
  try
{$IFNDEF VER100}
{$IFNDEF VER120}
    reg.Access := KEY_READ;
{$ENDIF}
{$ENDIF}
    reg.RootKey := HKEY_LOCAL_MACHINE;
    reg.OpenKey('\HARDWARE\DEVICEMAP\SERIALCOMM', false);
    debvalnames:=reg.GetValueNames(l);
    reg.GetValueNames(l);
    for n := 0 to l.Count - 1 do
    begin
      v.Add(reg.ReadString(l[n]));
    end;
    Result := v.CommaText;
  finally
    reg.Free;
    l.Free;
    v.Free;
  end;
end;   The purpose of the function is to return a string, containing
the list of the COM devices, attached to the computer. The bug occurs
when the number of the COM port is higher than 9 or exactly- last
digits of the COM number are trimmed. For example, my bluetooth device
is attached at COM32, but in the result of the function I get  COM3.
I have narrowed the search to the following code:
 Code: [Select]v.Add(reg.ReadString(l[n]));


I changed the code the following way:
 Code: [Select]ComName:= reg.ReadString(l[n]);
ShowMessage(length(ComName ) + '   ' + ComName);
v.Add(ComName);
If I put a breakpoint on the line with ShowMessage(...);  when the
application stops on it, when I put the mouse pointer over  ComName it
shows  „COM32“, or exactly what it should.
But, ShowMessage(length(ComName ) + '   ' + ComName);  shows  „COM3 
4“. It occurs that the last char is lost. If I have a longer port
number, probably last two chars will be lost.
So I did:
Code: [Select]ComName:= reg.ReadString(l[n]);
SetLength (ComName, 5);
ShowMessage(length(ComName ) + '   ' + ComName);
v.Add(ComName);
Now the last character is not lost, but I have a - (minus) sign in the
end of the shorter COM port names, which is not a surprise.
To recapitulate: The string is correctly retrieved from the registry,
but its length value is wrong. Is there a bug in windows itself, in
FPC (or Lazarus) registry module or in the posted code itself? And
what should I do to make it work. Definitely, I can trim the minus
signs, but that is the last chance solution.


Edit: I added anoher entry in the registry: COM252.
So, actually when using  SetLength (ComName, 5);  I get the following
strings „COM1“; „COM32-“; „COM33-“ and „COM252“. There are no minus
signs after  COM1 !!!
EDIT (again): Trough the registry editor I open the COM32 and COM33
values and then I pressed enter, just like editing them. Now the minus
signs disappeared! I removed the SetLength statement and still
everythings works fine.  Seems like the bluetooth device gets added
improperly?!?
Edit (once again): Now I remember, that some quotation marks " were
shown in the registry entry names, which have now disappeared. I will
move the bluetooth dongle to another usb port.

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derek.john.evans · 2014-10-24 12:42

Have you checked the binary encoding of the strings? (via regedit). 
Maybe its a widechar issue?

What version of Lazarus are you running?

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BigChimp · 2014-10-24 12:54

His signature mentions the Laz version...

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CM630 · 2014-10-24 13:02

Quote from: derek.john.evans on October 24, 2014, 02:42:15 pmHave you
checked the binary encoding of the strings? (via regedit).  Maybe its
a widechar issue?
I just did. So here is what I found out. It was 43 00 4F 00 4d 00 33
00 32 00. When I edited it (actually by only clicking OK in the
registry editor), it got changed to  43 00 4F 00 4d 00 33 00 32 00 00
00. Maybe there is a trick to use this info.

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derek.john.evans · 2014-10-24 13:39

Thats interesting. Looks like some registry writers arn't writing
correctly.

There is a StringSizeIncludesNull property, which is hardcoded to True
in winreg.inc

Which causes the string to be truncated in registry.pas
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i      If
StringSizeIncludesNull then       SetLength(Result, Info.DataSize-1) 
  else       SetLength(Result, Info.DataSize);     
It would seem, the code "should" check to see if the end char is
actually a #0, before truncating.

EDIT: I guess you will have to use your own version of ReadString() to
cater for the possible non nulled strings

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CM630 · 2014-10-24 14:28

I see at least tree possible reasons for that:
1. COM port adding to bluetooth in WinXP is buggy.
2. There is a problem in the driver of the  bluetooth dongle.
3. There is a problem in the device I am connecting to. It is a custom
one, so I might discuss it with the designer. But I cannot think why
it would have a connection to COM port assignment, so this does not
seem much possible to me.
Thanks for the ideas, I am done with Pascal for this week.

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CM630 · 2014-10-27 06:45

So I can definitely say, that the reason for that behaviour is item 1:
COM port adding to bluetooth in WinXP is buggy.
I have added my cell phone and the same problem occurred, which
rejected item 3 as a reason for the problem. Then replaced the
bluetooth dongle by a one by another manufacturer (or another model,
at least, definitely it is smaller than any of the ICs in the other
one). The problem reoccured, rejecting item 2 as a possible cause.


EDIT: I do wonder if there is not a buig in the FPC/Lazarus registry
functions? In a few days I could try this in another programming
language, to check how things are working there.