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How to open a serial COM port in Managed C++

, 16 Apr 2002
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How to open a Serial COM port using Managed C++ and loading unmanaged DLLs
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Many days ago, I was looking for a class in managed C++ that gives me access to the COM port. I was surprised I couldn't find anything to use. There were many classes to use for sockets and files, but none for COM ports.

I tried to use System::IO::File without any success. Actually File::Open gave me an exception. So I went ahead and created a class to handle serial COM ports. Please note I am using DllImport to import the kernel32.dll 

// Header File
__gc class CSerialPort
    __nogc struct DCB
        int DCBlength;
        int BaudRate;
        int fBinary;
        int fParity;
        int fOutxCtsFlow;
        int fOutxDsrFlow;
        int fDtrControl;
        int fDsrSensitivity;
        int fTXContinueOnXoff;
        int fOutX;
        int fInX;
        int fErrorChar;
        int fNull;
        int fRtsControl;
        int fAbortOnError;
        int fDummy2;
        unsigned short wReserved;
        unsigned short XonLim;
        unsigned char ByteSize;    //byte
        unsigned char Parity; // byte
        unsigned char StopBits;    //byte
        char XonChar;
        char XoffChar;
        char ErrorChar;
        char EofChar;
        char EvtChar;
        unsigned short wReserved1;

    bool    Open( char *szComPort);
    void    Write(String __gc * buf);
    String  *Read();
    void    Close();

    FileStream    * m_MyFileStream;
    StreamWriter * m_MyStreamWriter;
    StreamReader * m_MyStreamReader;
    static long GENERIC_READ  = 0x80000000L;
    static long GENERIC_WRITE = 0x40000000L;

    static int OPEN_ALWAYS = 4;

    static int FILE_FLAG_NO_BUFFERING = 0x20000000;
    static int FILE_FLAG_OVERLAPPED   = 0x40000000;


namespace MyKernel
extern bool SetCommState(System::IntPtr hFile, CSerialPort::DCB * lpDBC);
extern int CreateFile( char * lpFileName , int dwDesiredAccess, int dwShareMode,
  IntPtr lpSecurityAttributes, int dwCreationDisposition,
  int dwFlagsAndAttributes, IntPtr hTemplateFile );


Also note that I am creating a new namespace to use the imported functions from kernel32.dll

This is the cpp file:


bool CSerialPort::Open( char *szComPort)
    int handle;
    handle = MyKernel::CreateFile(

        IntPtr    pCom(handle);
        m_MyFileStream = new FileStream(pCom, 
                                        true, 1000, true);        

    catch (Exception  * e ) {
          return false;

    DCB    * CommSettings = new DCB();
    CommSettings->DCBlength = sizeof(CommSettings);
    CommSettings->BaudRate  = 38400;
    CommSettings->ByteSize  = 8;
    CommSettings->Parity    = 0;
    CommSettings->StopBits    = 1;


        m_MyStreamReader = new StreamReader(m_MyFileStream);

    catch (Exception  * e ) {
          return false;

    if ( m_MyFileStream->get_CanWrite() )
            m_MyStreamWriter = new StreamWriter(m_MyFileStream);

        catch (Exception  * e ) {
            return false;

    return true;

void CSerialPort::Write(String __gc * buf)

    catch (Exception  * e ) {

String  * CSerialPort::Read()
    String    *buf;
    buf = m_MyStreamReader->ReadLine();

    return (buf);

void CSerialPort::Close()

To use it:

CSerialPort * pSerial = new CSerialPort;


We open COM port 2 and we wait to read a LINE with \r\n or \n. If you waiting for bytes you need to change m_MyStreamReader->ReadLine() to m_MyStreamReader->Read().


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About the Author

Albert Pascual
Web Developer
United States United States
Al is just another Software Engineer working in C++, ASp.NET and C#. Enjoys snowboarding in Big Bear, and wait patiently for his daughters to be old enough to write code and snowboard.
Al is a Microsoft ASP.NET MVP

Comments and Discussions

GeneralI cannot SetCommState to return true. Pinmembernetlogging4-Apr-08 5:13 
QuestionException by FileStream Pinmemberstrizi2-Nov-07 0:16 
QuestionRe: Exception by FileStream Pinmembernetlogging4-Apr-08 5:46 
QuestionSample code Pinmemberstrizi2-Nov-07 0:14 
GeneralHi Pinmembertemikasali6-Aug-07 20:17 
Generalcode problem! PinmemberNenica16-Jun-04 13:15 
GeneralRe: code problem! PinmemberHristoBojkov20-Apr-05 22:18 
GeneralWin32 Application PinmemberNenica18-Feb-04 10:28 
GeneralRe: Win32 Application Pinmembersurajt14-May-04 9:00 
GeneralRe: Win32 Application PinmemberNenica16-Jun-04 13:12 
GeneralRe: Win32 Application PinmemberSharingan_Rasengan10-Jul-06 18:05 
GeneralRe: Win32 Application PinmemberSharingan_Rasengan10-Jul-06 18:05 
GeneralRe: Win32 Application Pinmembermertadin18-Jul-06 22:19 
GeneralRe: Win32 Application Pinmemberuptonryan19-Nov-06 20:46 
GeneralRe: Win32 Application PinmemberYaoTown11-Mar-08 18:08 
QuestionRe: Win32 Application Pinmembernetlogging4-Apr-08 5:47 
QuestionProject Files? PinsussUwe Komoss6-Aug-03 13:43 
QuestionWhat is the keywords __gc ? Pinmembergertano13-May-03 2:45 
AnswerRe: What is the keywords __gc ? PinmemberAlbert Pascual13-May-03 5:43 
GeneralRe: What is the keywords __gc ? Pinmembergertano13-May-03 10:09 
GeneralRe: What is the keywords __gc ? PinmemberAlbert Pascual13-May-03 12:53 
AnswerRe: What is the keywords __gc ? Pinmemberwadegiles6-Jul-05 6:13 
GeneralSerial comms sample code PinsussColin Bowdery3-Apr-03 1:26 
GeneralRe: Serial comms sample code Pinmemberwadegiles6-Jul-05 5:58 
Generalusing this class with visual c++ PinmemberSFH2-Apr-03 5:29 

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