Incorrect error returned for c'tor on windows

[dronesalot]

in win.cc line 85 there is the following line:
ss << "Unknown error opening the serial port: " << errno;

In fact the error code was returned from
DWORD errno_ = GetLastError();
So the line should really read:
ss << "Unknown error opening the serial port: " << errno_;

Ultimately I think it's not a good variable name anyway given that errno is already defined. The proper method should probably call FormatMessage to get the correct error message from the serial driver anyway. I can submit a patch if people think this is a good idea.

[dronesalot]

The following is functional although not really technically correct. It falls back to a big of an architectural problem because the IOException does not support a UNICODE error string of type wstring so the windows error has to be converted and may not work properly under foreign language versions of windows. I have also not taken into account any non-UNICODE implementations but this falls back to the old behaviour. I've also renamed errno_ to last_error to improve readability.

Someone with the right tools can probably generate a proper patch for this.

if (fd_ == INVALID_HANDLE_VALUE) {
DWORD last_error = GetLastError();
stringstream ss;
LPVOID lpMsgBuf=NULL;
switch (last_error) {
case ERROR_FILE_NOT_FOUND:
// Use this->getPort to convert to a std::string
ss << "Specified port, " << this->getPort() << ", does not exist.";
THROW (IOException, ss.str().c_str());
default:
// get the text error specific to this serial driver
#ifdef UNICODE
DWORD result=FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, last_error,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPTSTR) &lpMsgBuf, 0, NULL );
if (result) {
wstring err((WCHAR *)lpMsgBuf,(unsigned int)result);
string errstr(err.begin(),err.end());
ss << "Unknown error opening the serial port: " << errstr;
THROW (IOException, ss.str().c_str());
}
else {
ss << "Unknown error opening the serial port: " << last_error;
THROW (IOException, ss.str().c_str());
}
#else
ss << "Unknown error opening the serial port: " << last_error;
THROW (IOException, ss.str().c_str());
#endif
}
}