Writing to a Serial (Com) Port in Visual C++

serial-portvisual c++visual-studio-2008

I have a device that is connected on port COM4, (115200 baud, 8-N-1). Based on examples I found here I'm opening the port with:

                    Keyboard_Handle=CreateFile("\\\\.\\COM4",GENERIC_WRITE,0,NULL,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,NULL); 
                    if(GetLastError() !=0 || Keyboard_Handle == INVALID_HANDLE_VALUE)
                    {
                        AfxMessageBox("Error opening connection to Keyboard");
                        exit(1);
                    }


                    char buffer[100];
     strcpy(buffer,"baud=115200 parity=N data=8 stop=1");
     BuildCommDCB((char*)&buffer,&dcb)) 

     if(GetCommState(Keyboard_Handle, &dcb))
     {
      dcb.BaudRate = CBR_115200;
      dcb.ByteSize = 8;
      dcb.Parity = 0;
      dcb.StopBits = 1;
      SetCommState(Keyboard_Handle, &dcb);
     }

Later in my code I call WriteFile on the port with:

    LPDWORD bytes_written;
    LPDWORD bytes_read;
    LPOVERLAPPED OVERLAP;
    char write_buf[10];

    write_buf[0] = 's';
    write_buf[1] = '\0';

    if(Keyboard_Handle != NULL) {
    WriteFile(Keyboard_Handle, (LPCVOID)write_buf , strlen(write_buf), bytes_written, OVERLAP); 
    }

And every time I run the code I get the JIT Debugger complaining about an unhandled exception (though the WriteFile is inside a Try/catch block).

Is there something wrong with how I'm doing this?

Best Answer

bytes_written needs to be an address of a variable; the compiler wouldn't compile the statement you posted.

Likewise, "OVERLAP" doesn't make sense.

Did you check whether CreateFile succeeded?

What's in write_buf when you call strlen on it?

Try copy-and-pasting the actual code that you're using.

Also that doesn't seem like a very good/informative sample that you're using. Try Windows Serial Port Programming and http://msdn.microsoft.com/en-us/library/ms810467.aspx

Also start with the sample program from the Microsoft site, test it before you modify it (to check that it's working on your machine) and then modify it.

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