Symbolic links

[Terry Johnson]

This question is more of a windows question than com0com, but I'm asking it here in case someone happens to know ...

When com0com is installed, and a pair is created so that say com 5 and com 6 are mapped in, symbolic links are created Com5 maps to \Device\com0com10 and Com6 maps to \Device\com0com20

If you then add a printer that uses com5, the symlink is changed to \Device\NamedPipe\Spooler\Com5. This means you can no longer open Com5 as a serial port, even if the print queue isn't being used. I've seen similar behaviour with LPT ports, but sometimes you get a NONSPOOLED_LPT1 link back to the original port. Can anyone tell me if this is something I can do directly, or does it require device driver voodoo...

[Vyacheslav Frolov]

> I've seen similar behaviour with LPT ports, but sometimes
> you get a NONSPOOLED_LPT1 link back to the original port.

The following simple link NONSPOOLED_COM5 to the original port:

/////////////////////////////////////////////////////////////////
#include <windows.h>
#include <iostream>
using namespace std;

int main(int /*argc*/, char* /*argv[]*/)
{
  const char *pName = "COM5";
  const char *pAltName = "NONSPOOLED_COM5";

  char pathList[1000];

  if (!QueryDosDevice(pName, pathList, sizeof(pathList)/sizeof(pathList[0]))) {
    DWORD err = GetLastError();
    cerr << "QueryDosDevice: error - " << err << endl;
    return 1;
  }

  if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
    cerr << "QueryDosDevice: INSUFFICIENT BUFFER" << endl;
    return 1;
  }

  cout << pName << ":" << endl;

  char *p, *pPath = NULL;
  int j;

  for (p = pathList, j = 0 ; *p ; p += lstrlen(p) + 1, j++) {
    cout << "  " << j << ": " << p << endl;
    pPath = p;
  }

  if (pPath) {
    if (!DefineDosDevice(DDD_RAW_TARGET_PATH, pAltName, pPath)) {
      DWORD err = GetLastError();
      cerr << "DefineDosDevice: error - " << err << endl;
      return 1;
    }

    cout << "OK: " << pAltName << " --> " << pPath << endl;
  }

  return 0;
}
/////////////////////////////////////////////////////////////////

To be available NONSPOOLED_COM5 for HyperTerminal, you need also
add code to modify Registry or import to Registry the following file:

--- NONSPOOLED_COM5.reg ---
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM]
"\\Device\\com0com10"="NONSPOOLED_COM5"
---------------------------