Opening LPT port in C++

[CeZaR]

Hi,
I've posted earlier a question regarding the call to GetCommState.
Here is the code for the function.
The problem is that GetCommState always returns false!!
Why?

void Open()
{
// the DCB and COMMTIMEOUTS structure are declare a __value struct
DCB *dcbCommPort = __nogc new DCB();
COMMTIMEOUTS *ctoCommPort = __nogc new COMMTIMEOUTS();
// OPEN THE COMM PORT.
hComm = CreateFile("LPT1",GENERIC_READ | GENERIC_WRITE,0, 0,OPEN_EXISTING,0,0);
// IF THE PORT CANNOT BE OPENED, BAIL OUT.
if(hComm == INVALID_HANDLE_VALUE)
{
throw(new ApplicationException("Comm Port Can Not Be Opened"));
}
// SET THE COMM TIMEOUTS.
GetCommTimeouts(hComm,ctoCommPort);
ctoCommPort->ReadTotalTimeoutConstant = ReadTimeout;
ctoCommPort->ReadTotalTimeoutMultiplier = 0;
ctoCommPort->WriteTotalTimeoutMultiplier = 0;
ctoCommPort->WriteTotalTimeoutConstant = 0;
SetCommTimeouts(hComm,ctoCommPort);

// SET BAUD RATE, PARITY, WORD SIZE, AND STOP BITS.
GetCommState(hComm, dcbCommPort);
dcbCommPort->BaudRate=BaudRate;
dcbCommPort->flags=0;
//dcb.fBinary=1;
dcbCommPort->flags|=1;
if (Parity>0)
{
dcbCommPort->flags|=2;
}
dcbCommPort->Parity=Parity;
dcbCommPort->ByteSize=ByteSize;
dcbCommPort->StopBits=StopBits;
if (!SetCommState(hComm, dcbCommPort)) // always returns false
{
throw(new ApplicationException("Comm Port Can Not Be Opened"));
}
Opened = true;
}

Thanks!

 

[William DePalo [MVP VC++]]

I've posted earlier a question regarding the call to GetCommState.
Here is the code for the function.
The problem is that GetCommState always returns false!!

You shouldn't have to guess. _Immediately_ after the function returns, call
GetLastError().

Now, I haven't researched it, but if IJW is trampling on the thread's last
Win32 error by making some intervening Win32 API call, take a look at this:

http://blogs.msdn.com/adam_nathan/archive/2003/04/25/56643.aspx

Just by the way, is the LPT port in question controlled by a printer driver?

Regards,
Will

 

[CeZaR]

I've stopped the spooler service before running the program.
Then i call CreateFile with "\\\\.\\NONSPOOLED_LPT1".
BTW GetLastError returns 2 -> Invalid function.

 

[CeZaR]

And, finally i've fixed it!
The LPT port doesn't support all of the function in this code.
They all work for COM ports.
For LPT use just CreateFile, WriteFile.