Detect the status of a printer paper - delphi

Question

i need to get paper status information from a printer. I have a list of esc/pos commands.
I'm trying to send these comands with escape function
http://msdn.microsoft.com/en-us/library/windows/desktop/dd162701%28v=vs.85%29.aspx
This is my code
type
TPrnBuffRec = record
bufflength: Word;
Buff_1: array[0..255] of Char;
end;
procedure TFTestStampa.SpeedButton2Click(Sender: TObject);
var
Buff: TPrnBuffRec;
BuffOut: TPrnBuffRec;
TestInt: Integer;
cmd : string;
begin
printer.BeginDoc;
try
TestInt := PassThrough;
if Escape(Printer.Handle, QUERYESCSUPPORT, SizeOf(TESTINT),
#testint, nil) > 0 then
begin
cmd := chr(10) + chr(04) + '4';
StrPCopy(Buff.Buff_1, cmd);
Buff.bufflength := StrLen(Buff.Buff_1);
Escape(Printer.Canvas.Handle, Passthrough, 0, #buff,
#buffOut);
ShowMessage( conver(strPas(buffOut.Buff_1)) );
end
finally
printer.EndDoc;
end;
function TFTestStampa.Conver(s: string): String;
var
i: Byte;
t : String;
begin
t := '';
for i := 1 to Length(s) do
t := t + IntToHex(Ord(s[i]), 2) + ' ';
Result := t;
end;
Problem is with different cmds I obtain always the same string ....
Can you give me an example of escape function with last parameter not nill ?
Alternatives to obtain paper status ?

Answer 1

I suppose you are using Delphi 2009 above and you used this source for your example, so your problem might be caused by Unicode parameters. In Delphi since version 2009, string type is defined as UnicodeString whilst in Delphi 2009 below as AnsiString, the same stands also for Char which is WideChar in Delphi 2009 up and AnsiChar below.
If so, then I think you have a problem at least with your buffer data length, because Char = WideChar takes 2 bytes and you were using StrLen function which returns the number of chars what cannot correspond to the data size of number of chars * 2 bytes.
I hope this will fix your problem, but I can't verify it, because I don't have your printer :)
type
TPrinterData = record
DataLength: Word;
Data: array [0..255] of AnsiChar; // let's use 1 byte long AnsiChar
end;
function Convert(const S: AnsiString): string;
var
I: Integer; // 32-bit integer is more efficient than 8-bit byte type
T: string; // here we keep the native string data type
begin
T := '';
for I := 1 to Length(S) do
T := T + IntToHex(Ord(S[I]), 2) + ' ';
Result := T;
end;
procedure TFTestStampa.SpeedButton2Click(Sender: TObject);
var
TestInt: Integer;
Command: AnsiString;
BufferIn: TPrinterData;
BufferOut: TPrinterData;
begin
Printer.BeginDoc;
try
TestInt := PASSTHROUGH;
if Escape(Printer.Handle, QUERYESCSUPPORT, SizeOf(TestInt), #TestInt, nil) > 0 then
begin
Command := Chr(10) + Chr(04) + '4';
StrPCopy(BufferIn.Data, Command);
BufferIn.DataLength := StrLen(Command);
FillChar(BufferOut.Data, Length(BufferOut.Data), #0);
BufferOut.DataLength := 0;
Escape(Printer.Canvas.Handle, PASSTHROUGH, 0, #BufferIn, #BufferOut);
ShowMessage(Convert(StrPas(BufferOut.Data)));
end
finally
Printer.EndDoc;
end;
end;