🚀 go-pugleaf

Hi

I have an application that occasionally (about 10% of the time) generates
the error 'list index out of bounds' on execution, but I have yet to see the
error while running the project via the debugger. I have listed the code
below. Can anyone see any  possible problems with the code?

Basically, the application gets the username of the person logged on from
windows and then queries an MS Access database using this data to see if a
persons details exist. Because of problems with >30 users accessing the
database simultanioulsy (very slow network at times) The database is queried
in a randomly generated timer procedure.

any help appreciated.


code:

// get the name of the station, in the form normally in the form T11-20
where T11 is room and 20 is staion number
function getStationName:string;
var
    stationName    : string;
    stationNameLen : Dword;
begin
    stationNameLen := 255;
    SetLength(stationName, stationNameLen);
    If GetComputerName(PChar(stationName), stationNameLen) Then
            Result := Copy(stationName,1,stationNameLen - 1)
    Else
            Result := 'Unknown';
End;

// get the the username of person logged on. normally digit,digit, then 6
char
Function GetUserFromWindows: string;
Var
  UserName    : string;
  UserNameLen : Dword;
Begin
  form1.Text:='getting username';
  UserNameLen := 255;
  SetLength(userName, UserNameLen);
  If GetUserName(PChar(UserName), UserNameLen) Then
    Result := Copy(UserName,1,UserNameLen - 1)
  Else
    Result := 'Unknown';
End;


// check if there are details in MS Access database for this user
function tform1.UserInDatabase:boolean;
var
        tryagain:boolean;
begin
        form1.Text:='checking for user in database';
        {search for an entry in students table that matches the username}
        ADOQuery.Close;
        with ADOQuery do
            begin
            sql.clear;
            sql.add('select * from students where userName =?');
            Parameters[0].value := user;
            end;
        tryagain:=true;
        while tryagain do
            begin
            tryagain:=false;
            try
                ADOQuery.Open;
            except
                begin
                messageDlg('Unable to open query',mterror,[mbok],0);
                tryagain:=true; {unable to open query so try again}
                end;
           end;
        if (ADOQuery.fieldbyname('forename').asstring='') then
            begin
            messageDlg('Call your teacher, details for '+user+' do not
exist',mterror,[mbok],0);
            UserInDatabase:=false;
            end
        else UserInDatabase:=true;
        end;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
        name:string;
        time:integer;
        stationName:string;
        dummy:integer;
begin
        firstTime:=true;
        form1.Text:='activating UDP';
        idUDPServer1.Active := True;
        form1.Text:='get username';
        user:=GetUserFromWindows;
        form1.Text:=user;
        stationName:=getStationName;
        room:=stationName[1]+stationName[2]+stationName[3];
        Randomize;
        file://prevent timer interval of 0
        repeat
            time:= Random(200);
        until time>0;

        time:=time*100;
        form1.Text:='timer int:'+inttostr(time);
        timer1.interval:=time;
        timer1.Enabled:=true;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var
name:string;
begin
timer1.enabled:=false;
if UserInDatabase then
        begin
        form1.Text:='user in database';
        name:=ADOQuery.fieldbyname('forename').asstring+ '
'+ADOQuery.fieldbyname('surname').asstring;
        form1.Text:=name;
        end;
end;