Invalid parameter error using GetDefaultCommConfig - c++

Question

I came up with the same issue,in which I got a LPTSTR portname param as input from a function.I have to convert this into wstring,so that I can fetch the Port paramaters.
below is the code snippet in which am trying to copy lptstr to wstring.
void C_PORT_MONITOR::SetPrinterComPortParam(LPTSTR PortName)
{
#ifdef _UNICODE
std::wstring l_ComPortName;
#else
std::string l_ComPortName;
#endif
DWORD dwSize,le = 0;
dwSize = sizeof(COMMCONFIG);
LPCOMMCONFIG lpCC = (LPCOMMCONFIG) new BYTE[dwSize];
l_ComPortName = PortName;//mPortName;
if(l_ComPortName.length() <= 0 )
return;
bool SetFlag = false;
//Get COMM port params called to get size of config. block
int length = l_ComPortName.length();
int iPos = l_ComPortName.find_first_of(':');
int iChc = length- iPos; //remove the charactrers after :
l_ComPortName = l_ComPortName.substr(0, (length- iChc)); //remove the characters from colon //COM1
//Get COMM port params with defined size
BOOL ret = GetDefaultCommConfig(l_ComPortName.c_str(), lpCC, &dwSize);
_RPT1(_CRT_WARN, "C_PORT_MONITOR::SetPrinterComPortParam length=%x,iPos=%x,iChc=%x,l_ComPortName=%s",length, iPos, iChc, l_ComPortName);
if(!ret)
{
le = GetLastError();
_RPT1(_CRT_WARN ,"C_PORT_MONITOR::SetPrinterComPortParam LastError=%x",le);
}
I need to assign this portname to l_comportname. and I need to create a substring from this l_comportname as COM1 and I have to use this substring in getdafaultcommconfig()

Answer 1

Your error is the second parameter not the first. Your debugging statement is bugged because it doesn't account for wide strings %s is for narrow strings only, you should use %S for a wide string.
Here's the real error
dwSize = sizeof(COMMCONFIG);
LPCOMMCONFIG lpCC = (LPCOMMCONFIG) new BYTE[dwSize];
lpCC->dwSize = sizeof(COMMCONFIG); // this line is needed
You might need this as well (the documentation isn't very clear)
lpCC->wVersion = 1;
It's very common in Windows programming that you have to initialize a struct with the size of the struct.
Ref: https://technet.microsoft.com/en-us/aa363188(v=vs.90)