Question

I am currently trying to implement a serial port reader class using Windows (already implemented one using Boost, want to cater for the possibility that the platform may not have Boost).

All seems to be working well, except when I test my Windows serial port reader (executable) using my Boost serial port writer (a separate executable), the writer throws an access denied exception. Otherwise the reader works, as it seems to be reading whatever is on the serial port up until the point that the writer can no longer write.

It doesn’t matter whether the writer is started first or the reader is started first, once the reader opens the port for reading, the writer can no longer write to that port.

I have tried setting different arguments in the CreateFile() method but to no avail so far, I would expect the following code snippet to work but it doesn’t.

m_serial = CreateFile(
    m_port, 
    GENERIC_READ, 
    FILE_SHARE_WRITE, 
    0, 
    OPEN_EXISTING, 
    FILE_ATTRIBUTE_NORMAL, 
    0);

The writer code may be irrelevant but here it is anyway:

void writeLine(std::string line) 
{
    boost::asio::io_service io;
    boost::asio::serial_port serial(io, m_port);

    serial.set_option(boost::asio::serial_port_base::baud_rate(m_rate));

    boost::asio::write(serial, boost::asio::buffer(line.c_str(), line.size()));

}

And the .what() for the boost::system::system_error is:

open: Access is denied

Any ideas?

I’ve looked here: http://www.robbayer.com/files/serial-win.pdf (great article, but doesn’t go that far) and http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858(v=vs.85).aspx – seems like it should be the dwShareMode argument but I can’t get it working.

Edit: I should mention I am using this serial port emulator http://www.eterlogic.com/Products.VSPE.html which may well be the cause of my woes, if so then it doesn’t matter. The emulator works as expected when using my Boost reader with my Boost writer though (from two separate executables).

Answer 1

I can understand why there have been no replies now. For the record, the arguments to open the serial port were fine. The problem was that I was attempting to open the same port for each read without closing it, so I’ve just left it open until I’ve completed finished with it.