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Posted 16 Apr 2002

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 

<pre lang=mc++>// 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:

<pre lang=mc++>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;


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


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Comments and Discussions

GeneralI cannot SetCommState to return true. Pin
netlogging4-Apr-08 6:13
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QuestionException by FileStream Pin
strizi2-Nov-07 1:16
memberstrizi2-Nov-07 1:16 
QuestionRe: Exception by FileStream Pin
netlogging4-Apr-08 6:46
membernetlogging4-Apr-08 6:46 
QuestionSample code Pin
strizi2-Nov-07 1:14
memberstrizi2-Nov-07 1:14 
GeneralHi Pin
temikasali6-Aug-07 21:17
membertemikasali6-Aug-07 21:17 
Generalcode problem! Pin
Nenica16-Jun-04 14:15
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GeneralRe: code problem! Pin
HristoBojkov20-Apr-05 23:18
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GeneralWin32 Application Pin
Nenica18-Feb-04 11:28
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GeneralRe: Win32 Application Pin
surajt14-May-04 10:00
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GeneralRe: Win32 Application Pin
Nenica16-Jun-04 14:12
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GeneralRe: Win32 Application Pin
Sharingan_Rasengan10-Jul-06 19:05
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GeneralRe: Win32 Application Pin
Sharingan_Rasengan10-Jul-06 19:05
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GeneralRe: Win32 Application Pin
mertadin18-Jul-06 23:19
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GeneralRe: Win32 Application Pin
uptonryan19-Nov-06 21:46
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GeneralRe: Win32 Application Pin
YaoTown11-Mar-08 19:08
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QuestionRe: Win32 Application Pin
netlogging4-Apr-08 6:47
membernetlogging4-Apr-08 6:47 
QuestionProject Files? Pin
ukomoss6-Aug-03 14:43
memberukomoss6-Aug-03 14:43 
QuestionWhat is the keywords __gc ? Pin
gertano13-May-03 3:45
membergertano13-May-03 3:45 
AnswerRe: What is the keywords __gc ? Pin
Albert Pascual13-May-03 6:43
sitebuilderAlbert Pascual13-May-03 6:43 
GeneralRe: What is the keywords __gc ? Pin
gertano13-May-03 11:09
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GeneralRe: What is the keywords __gc ? Pin
Albert Pascual13-May-03 13:53
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AnswerRe: What is the keywords __gc ? Pin
wadegiles6-Jul-05 7:13
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GeneralSerial comms sample code PinPopular
Colin Bowdery3-Apr-03 2:26
memberColin Bowdery3-Apr-03 2:26 
GeneralRe: Serial comms sample code Pin
wadegiles6-Jul-05 6:58
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Generalusing this class with visual c++ Pin
SFH2-Apr-03 6:29
memberSFH2-Apr-03 6:29 

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