Send string to USB virtual port USB001 (Windows)

AleksM

My Windows application needs to send a QString to the USB001 port in order to print a document to a specific printer (ZPL format to a Zebra printer). Ideally I would copy a file to that port or send it somehow.

Anybody has an advice?

Related problem with QPrinter is posted here.

VRonin

QSerialPort + QDataStream/QTextStream

Please note you probably want to send a QLatin1String or a QByteArray rather than a QString

mrjj

Hi
Reminds me of the good old times where we did

share virtual USB001 port as "printersharename"
net use lpt1: \\computername\printersharename /persistent:yes
COPY /B test.txt LPT1

:)

AleksM

@VRonin Thanks. I tried, but only COM1 is available in my system. USB001 is a virtual printer port (Win 7 and Win 10), or I need to do something extra to map it. No clue.

AleksM

@mrjj Right, this works but it is not acceptable for the user to do net use when configuring the printer. Thanks.

mrjj

@AleksM
Well you could run it via QProcess and hook up from application but I agree
its a bit hackish.

mrjj

Hi
Just as a note.
As far as i know, its not possible with QPainter to send raw commands
to a printer and native API may be the only solution
https://support.microsoft.com/en-us/help/138594/howto-send-raw-data-to-a-printer-by-using-the-win32-api

Could be wrong though as i only dig around for some hours.

AleksM

@mrjj Thanks, mrjj! This is an alternative, but probably a QProcess with print batch file is more acceptable. Copy to network printer works within a batch file, but not with QFile::copy() !?

I am just curious if I can use USB001 port directly, from QT, but I am out of ideas at the moment.

aha_1980

@AleksM Have you read this SO thread? https://stackoverflow.com/questions/4442122/send-raw-zpl-to-zebra-printer-via-usb

mrjj

@AleksM
I think cmd copy /b knows the something about LPT1 that
QFile::copy do not. (since LPT1 is a special target)

Note:
While doing research i did see, and comments suggested it worked but
i have not tested it.

std::ifstream input("c:\\test", std::ios::binary);
if (input) {
    std::ofstream("lpt1", std::ios::binary) << input.rdbuf();
}
else {
    std::cerr << "ERROR: failed to open 'c:\\test' for reading\n";
}

AleksM

@aha_1980

Thanks aha_1980! I did not read it before. It is promising, but it does not work for me yet.

There are some fragments of the ZPL in a saved file (instead of printing), but some parts are transformed and some tags are added before and after. I need to experiment and troubleshoot a bit more.