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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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Introduction

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
{
public:
    CSerialPort(void);
    __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();

private:    
    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
{
[DllImport("kernel32.dll")]
extern bool SetCommState(System::IntPtr hFile, CSerialPort::DCB * lpDBC);
[DllImport("kernel32.dll")]
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:

CSerialPort::CSerialPort(void)
{
}

bool CSerialPort::Open( char *szComPort)
{
    int handle;
            
    handle = MyKernel::CreateFile(
        szComPort,
        GENERIC_READ | GENERIC_WRITE,
        0,
        NULL,
        OPEN_ALWAYS,
        FILE_FLAG_NO_BUFFERING | FILE_FLAG_OVERLAPPED,
        NULL);

    try
    {
        IntPtr    pCom(handle);
        m_MyFileStream = new FileStream(pCom, 
                                        FileAccess::ReadWrite, 
                                        true, 1000, true);        
    }

    catch (Exception  * e ) {
        Console::WriteLine(e->ToString());
          return false;
      }

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

    MyKernel::SetCommState(m_MyFileStream->get_Handle(), 
                           CommSettings);
    

    try
    {
        m_MyStreamReader = new StreamReader(m_MyFileStream);
    }

    catch (Exception  * e ) {
        Console::WriteLine(e->ToString());
          return false;
      }

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

        catch (Exception  * e ) {
            Console::WriteLine(e->ToString());
            return false;
        }
    }

    return true;
}

void CSerialPort::Write(String __gc * buf)
{
    try
    {
        m_MyStreamWriter->Write(buf);
        m_MyStreamWriter->Flush();    
        
    }

    catch (Exception  * e ) {
        Console::WriteLine(e->ToString());    
      }
}

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

    return (buf);
}

void CSerialPort::Close()
{
    m_MyStreamWriter->Close();
    m_MyStreamReader->Close();
    m_MyFileStream->Close();
}

To use it:

CSerialPort * pSerial = new CSerialPort;

pSerial->Open(S"COM2:");
Console::WriteLine(pSerial->Read());

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().

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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
 
Blog

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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