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Odd registry behaviour in WinXP

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While fixing a bug in LazSerial I got to synaser. Here is the problematic code:

--- Code: ---function GetSerialPortNames: string;
  reg: TRegistry;
  l, v: TStringList;
  n: integer;
  debvalnames: string;
  l := TStringList.Create;
  v := TStringList.Create;
  reg := TRegistry.Create;
    reg.Access := KEY_READ;
    reg.RootKey := HKEY_LOCAL_MACHINE;
    for n := 0 to l.Count - 1 do
    Result := v.CommaText;
--- End code ---
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: ---v.Add(reg.ReadString(l[n]));
--- End code ---

I changed the code the following way:
--- Code: ---ComName:= reg.ReadString(l[n]);
ShowMessage(length(ComName ) + '   ' + ComName);

--- End code ---
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: ---ComName:= reg.ReadString(l[n]);
SetLength (ComName, 5);
ShowMessage(length(ComName ) + '   ' + ComName);

--- End code ---
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.

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

What version of Lazarus are you running?

His signature mentions the Laz version...


--- Quote from: derek.john.evans on October 24, 2014, 02:42:15 pm ---Have you checked the binary encoding of the strings? (via regedit).  Maybe its a widechar issue?

--- End quote ---
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.

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

There is a StringSizeIncludesNull property, which is hardcoded to True in

Which causes the string to be truncated in registry.pas

--- Code: Pascal  [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---     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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