Correct way to send commands directly to printer!

Question

Ok, here is how i do it:

procedure TMainWindow.btnRawPrintClick(Sender: TObject);
begin
  BeginPrint;
  SendStr(#27#69);
  SendStr(\'MyData\');
  SendStr(#10         


        

Answer 1

Your current code is sending data to the printer in the wrong format due to changes between Ansi and Unicode characters. The printer you're using is evidently able to tolerate some amount of error, which is why some of your commands worked, but there's a limit.

In your version of Delphi, Char is equivalent to WideChar, so change your Char code to use AnsiChar instead, so you can send one-byte characters, as the printer expects. Your PrintRawData function was fine before. Your change is wrong. The printer does not expect to receive two-byte Unicode characters, but that's what your change amounts to.

After restoring the original PrintRawData code, change your SendStr function to this:

procedure TMainWindow.SendStr(const Text: string);
var
  data: AnsiString;
begin
  data := Text;

  if (PrintRawData(printHandle,
                   PAnsiChar(data),
                   Length(data)) < 0) then begin
    ShowMessage('PrintRawData Failed');
    EndRawPrintPage(printHandle);
    EndRawPrintJob(printHandle);
  end;
end;

I made the following changes to the code:

1. Replace the Char array with an AnsiString.
2. Instead of growing the data array one character at a time with a loop, do the Unicode-to-Ansi conversion with a single assignment statement and let the RTL take care of the conversion.
3. Type-cast the data string to PAnsiChar for passing to PrintRawData.
4. Pass string parameters as const unless you need to modify their contents.
5. No need for an explicit exit statement when the function is already finished.