[SOLVED] Printing to a [Zebra] CUPS printer from my Qt application

DiBosco · 10-02-2011, 05:21 AM

I have written a Qt4 app and need to print to my barcode printer. I can create a valid barcode file and if I use cutecom to copy this file via the printer's serial port it prints the label, so I know I am producing the correct information.

I am having problems with CUPS though. Test pages print blank for a start. At first if I called the cups API with this kind of thing:

Code:

	jobId = cupsCreateJob( CUPS_HTTP_DEFAULT, printer_name, job_name, 0, NULL );

	if ( jobId > 0 )
	        {
		const char* format = CUPS_FORMAT_TEXT;  // CUPS_FORMAT_POSTSCRIPT;

		cupsStartDocument( CUPS_HTTP_DEFAULT, printer_name, jobId, text, format, true );
// text is the ASCII string sent that can be sent via the serial port and works
		cupsWriteRequestData( CUPS_HTTP_DEFAULT, text, strlen( text ) ); 

		cupsFinishDocument( CUPS_HTTP_DEFAULT, printer_name );
	        }

It would print text rather than the barcode. Now I can't get anything out of it. I think I should be able to do something like:

lp -d S4M zebra.zpl

To send the file to the printer and, indeed, you can see the printer receives data but prints nothing out.

Is there something different/extra I need to do when using CUPS rather than the serial port for getting a printer to actually print out?

Thanks!

dwhitney67 · 10-02-2011, 07:34 AM

I've worked with the CUPS library before, however when I printed, the text came from a file. I do not know if that makes a difference. Do you know if your specialized printer requires text-formatted data, or does it accept postscript-formatted only? You seem to be certain that it is text only.

Here's some code I played with in the past (written in C++); it is very similar to yours in a lot of respects:

Code:

int
PrintUtility::print(std::istream& is, const char* filename)
{
   int jobId = 0;

   if (is.good() && !myPrinterName.empty())
   {
      collectOptions();

      jobId = cupsCreateJob(CUPS_HTTP_DEFAULT, myPrinterName.c_str(), filename,
                            myNumOptions, myOptions);

      if (jobId > 0)
      {
         const char* format = (std::string(filename).find(".ps") != std::string::npos ?
                               CUPS_FORMAT_POSTSCRIPT : CUPS_FORMAT_TEXT);

         char buffer[4096] = {0};
         snprintf(buffer, sizeof(buffer) - 1, "%s", filename);

         cupsStartDocument(CUPS_HTTP_DEFAULT, myPrinterName.c_str(), jobId, buffer, format, true);

         while (is.good())
         {
            is.read(buffer, sizeof(buffer));

            if (is.gcount() > 0)
            {
               cupsWriteRequestData(CUPS_HTTP_DEFAULT, buffer, is.gcount());
            }
         }

         cupsFinishDocument(CUPS_HTTP_DEFAULT, myPrinterName.c_str());
      }

      releaseOptions();
   }

   return jobId;
}

DiBosco · 10-02-2011, 08:05 AM

Well, I am pretty sure it's just a text thing. If I copy a text file to its serial port it prints out fine, and the ZPL language datasheet just goes on about ASCII characters.

Yours does indeed look very similar to mine. I've seen lots of people say this is doable, and I am sure I'm just missing something basic that would make it spring in to life! Just can't suss it though.

DiBosco · 10-03-2011, 11:46 AM

OK, just in case this helps someone else, forget about it being a Zebra printer, set it up as a raw stream.