DeviceCapabilities of a network printer - c++

Question

I'm trying to get list of supported page sizes of network printer using DeviceCapabilities and completely confused with sPort parameter.
DWORD nPapersCount = ::DeviceCapabilities(sPrinter, sPort, DC_PAPERS, nullptr, nullptr);
Could anyone suggest me, what should I provide in sPort for network printer and how could I reliably obtain that port?
As experiment, I have tried PC name in format "\\Share", its port "\\Share\LPT1", just "LPT1" and have no luck.
Also, I've found EnumPorts function, so I could obtain a list of printer ports on remote server, but I have no idea how to deal with list of ports i n case of multiple printers on server.
typedef struct _PORT_INFO_2 {
LPTSTR pPortName;
LPTSTR pMonitorName;
LPTSTR pDescription;
DWORD fPortType;
DWORD Reserved;
} PORT_INFO_2, *PPORT_INFO_2;

Answer 1

You can't guess the portname, specially in case of network printers. Use PrintDlg to get information from currently selected printer (this can be done without showing the print dialog).
Portname is available through hDevNames member of PRINTDLG structure.
DEVNAMES structure:
typedef struct tagDEVNAMES {
WORD wDriverOffset;
WORD wDeviceOffset;
WORD wOutputOffset; //<= port name
WORD wDefault;
} DEVNAMES, *LPDEVNAMES;
Unicode example:
PRINTDLG pdlg = { sizeof PRINTDLG };
pdlg.Flags = PD_RETURNDEFAULT;
PrintDlg(&pdlg);
LPDEVNAMES lpDev = (LPDEVNAMES)GlobalLock(pdlg.hDevNames);
std::wstring device = (LPCTSTR)lpDev + lpDev->wDeviceOffset;
std::wstring port = (LPCTSTR)lpDev + lpDev->wOutputOffset;
::GlobalUnlock(pdlg.hDevNames);
//clean up after PrintDlg, as pointed out by #RemyLebeau
GlobalFree(pdlg.hDevMode);
GlobalFree(pdlg.hDevNames);
int nPapersCount;
nPapersCount = ::DeviceCapabilities(device.c_str(), port.c_str(), DC_PAPERS, NULL, NULL);
if (nPapersCount > 0)
{
WORD* sizeBuf = new WORD[nPapersCount];
DeviceCapabilities(device.c_str(), port.c_str(), DC_PAPERS, (LPTSTR)sizeBuf, NULL);
for (int i = 0; i < nPapersCount; i++)
std::wcout << sizeBuf[i] << "\n";
delete[] sizeBuf;
}

Answer 2

Using PrintDlg is a little unwieldy, and has the disadvantage that it only lets you query the default printer (AFAIK). The better bet is to use GetPrinter, with a requested output level of 5:
HANDLE h = NULL;
OpenPrinter(printerName, &h, NULL); // printerName is a LPWSTR
if (!h)
return;
DWORD cbBuf=0;
GetPrinter(h, 5, NULL, 0, &cbBuf);
// First call to GetPrinter determines an output buffer size
BYTE *buf = new BYTE[cbBuf];
if (!GetPrinter(h, 5, buf, cbBuf, &cbBuf))
{ ClosePrinter(h); return; }
PRINTER_INFO_5 *ppi = (PRINTER_INFO_5*) buf;
LPWSTR port = ppi->pPortName;
ClosePrinter(h);