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CSerialPort v1.03 - Serial Port Wrapper

, 3 Mar 2000
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A freeware MFC class for Win32 serial ports.

Introduction

Welcome to CSerialPort, a freeware MFC class to wrap access to the Win32 APIs dealing with serial ports.

Features

  • Simple and clean C++ interface.
  • Uses C++ exceptions in preference to the normal Win32 return value mechanism. This ensures that code which uses CSerialPort is more robust.
  • Unicode enabled, supports linking to MFC statically and all code compiles cleanly at warning level 4.
  • Supports overlapped, blocking and callback usage models of the serial port. (Callback is only supported on NT).

Usage

  • To use the class in your code, simply include serialport.cpp in your project and #include serialport.h in which ever of your modules needs to make calls to the class.
  • To see the code in action, have a look at the module app.cpp in the sample app.

A brief example is as follows:

try {
    CSerialPort port;
    port.Open(1, 1200, CSerialPort::NoParity, 8, 
      CSerialPort::OneStopBit, 
      CSerialPort::XonXoffFlowControl);

    char sBuf[] = "This should appear on the serial port";
    port.Write(sBuf, strlen(sBuf));

    port.Flush();

    port.Close();
}
catch (CSerialException* pEx)
{
    TRACE(_T("Handle Exception, Message:%s\n"), 
                      pEx->GetErrorMessage());
    pEx->Delete();
}

History

  • V1.0 (31st May 1999)
    • Initial public release.
  • V1.01 (3rd June 1999)
    • Fixed problem with code using CancelIo function which does not exist on 95.
    • Fixed leaks which can occur in sample app when an exception is thrown.
  • V1.02 (16th June 1999)
    • Fixed a bug whereby CString::ReleaseBuffer was not being called in CSerialException::GetErrorMessage.
  • V1.03 (29th September 1999)
    • Fixed a simple copy and paste bug in CSerialPort::SetDTR.

APIReference

The API consists of the classes: CSerialException and CSerialPort. They have the following member functions and variables:

CSerialException::CSerialException

CSerialException( DWORD dwError = 0);

Parameters

dwError - The error that caused the exception.

Remarks

This member function is called when a CSerialException object is created. To throw a CSerialException, call the global function AfxThrowSerialException. If you call it using the default value for dwError, then internally it will call GetLastError for you.

CSerialException::GetErrorMessage

virtual BOOL GetErrorMessage( LPTSTR lpszError, 
      UINT nMaxError, PUINT pnHelpContext = NULL );
CString GetErrorMessage();

Return Value

  1. Nonzero if the function is successful; otherwise 0 if no error message text is available.
  2. A CString representation of the error.

Parameters

  • lpszError - A pointer to a buffer that will receive an error message.
  • nMaxError - The maximum number of characters the buffer can hold, including the NULL terminator.
  • pnHelpContext - The address of a UINT that will receive the help context ID. If NULL, no ID will be returned.

Remarks

Call this member function to provide text about an error that has occurred.

CSerialException::m_dwError

Remarks

The error that caused the exception. This error value is a system error code as found in WINERROR.H.

For a list of Win32 error codes, see Error Codes in the Win32 SDK.

CSerialPort::CSerialPort

CSerialPort();

Remarks

Standard C++ constructor for the class. Internally it just sets up the member variables to default values.

CSerialPort::~CSerialPort

~CSerialPort();

Remarks

Standard C++ destructor for the class. It will ensure that the comms port is closed if it is open.

CSerialException::Open

void Open( int nPort, DWORD dwBaud = 9600, 
  Parity parity = NoParity, BYTE DataBits = 8, 
  StopBits stopbits = OneStopBit, 
  FlowControl fc = NoFlowControl, BOOL bOverlapped = FALSE);
throw( CSerialException );

Parameters

  • nPort - The communications port to open.
  • dwBaud - The baud rate to use
  • parity - The parity to use. parity is an enum with the following values:
     enum Parity
        { 
        EvenParity,
        MarkParity,
        NoParity,
        OddParity,
        SpaceParity
        };
  • Databits - The number of data bits to use.
  • stopbits - The number of stop bits to use. stopbits is an enum with the following values:
     enum StopBits
        {
        OneStopBit,
        OnePointFiveStopBits,
        TwoStopBits
        }; 
  • fc - The flow control method to use. fc is an enum with the following values:
    enum FlowControl
    {
    NoFlowControl,
    CtsRtsFlowControl,
    CtsDtrFlowControl,
    DsrRtsFlowControl,
    DsrDtrFlowControl,
    XonXoffFlowControl
    }; 
  • bOverlapped - TRUE if you want to open in overlapped mode, otherwise FALSE to use blocking calls.

Remarks

Call this member function to open a communications port. Internally the class will use CreateFile to open the comms port (handling the case where the port number if greater than 9) and then uses SetState to set the various RS-232 settings as specified via the function parameters. If an error occurs, a CSerialException will be thrown.

CSerialPort::Close

Close();

Remarks

The corollary function to Open. Just closes the comms port if already open.

CSerialPort::Attach

void Attach(HANDLE hComm);

Parameters

hComm - The SDK handle of the open comms port.

Remarks

Allows you to attach a CSerialPort instance to an existing SDK comms port handle. This function is similar in behavior to the CWnd::Attach function provided in MFC.

CSerialPort::Detach

HANDLE Detach();

Return Value

The SDK comms port HANDLE.

Remarks

Corollary function to Attach. This function is similar in behavior to the CWnd::Detach function provided in MFC.

CSerialPort::operator HANDLE

operator HANDLE();

Return Value

The SDK comms port HANDLE.

Remarks

Use this operator to get the handle of the underlying comms port. You can use this handle to call the Windows APIs directly.

CSerialPort::IsOpen

BOOL IsOpen() const

Return Value

TRUE if the comms port is open, otherwise FALSE.

CSerialPort::Dump

void Dump(CDumpContext& dc) const

Remarks

Standard MFC diagnostic support function.

CSerialPort::Read\ReadEx

DWORD Read(void* lpBuf, DWORD dwCount);
BOOL Read(void* lpBuf, DWORD dwCount, OVERLAPPED& overlapped);
void ReadEx(void* lpBuf, DWORD dwCount);
    throw( CSerialException );

Return Value

  1. The number of bytes read.

  2. TRUE if the overlapped read completed synchronously, FALSE if the operation is to be completed asynchronously.

Parameters

  • lpBuf - Points to the buffer to read the data into from the serial port.
  • dwCount - Specifies the number of bytes to read from the serial port.
  • overlapped - reference to an OVERLAPPED structure. This is required if the port was opened in overlapped mode.

Remarks

These 3 functions are wrappers for the SDK calls ReadFile and ReadFileEx. The 2nd version of Read is the overlapped version.

CSerialPort::Write\WriteEx

DWORD Write(const void* lpBuf, DWORD dwCount);
BOOL Write(const void* lpBuf, DWORD dwCount, OVERLAPPED& overlapped);
void WriteEx(const void* lpBuf, DWORD dwCount);
    throw( CSerialException );

Return Value

  1. The number of bytes written.

  2. TRUE if the overlapped write completed synchronously, FALSE if the operation is to be completed asynchronously.

Parameters

  • lpBuf - Points to the buffer containing the data to be written to the serial port.
  • dwCount - Specifies the number of bytes to write to the serial port.
  • overlapped - reference to an OVERLAPPED structure. This is required if the port was opened in overlapped mode.

Remarks

These 3 functions are wrappers for the SDK calls WriteFile and WriteFileEx. The 2nd version of Write is the overlapped version.

CSerialPort::TransmitChar

void TransmitChar(char cChar) const
   throw( CSerialException );

Remarks

Simple wrapper for the TransmitCommChar SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetOverlappedResult

void GetOverlappedResult(OVERLAPPED& overlapped, 
        DWORD& dwBytesTransferred, BOOL bWait)
    throw( CSerialException );

Remarks

Simple wrapper for the GetOverlappedResult SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::CancelIo

void CancelIo()
    throw( CSerialException );

Remarks

Simple wrapper for the CancelIo SDK function call. See the Win32 SDK documentation for further details. Please note that this function is only available on NT 4, or Windows 98 or later. In version 1.0 of CSerialPort, this would cause code developed with it to fail to load on Windows 95 with an error about a missing export. This problem has been rectified in v1.01 of CSerialPort.

CSerialPort::GetConfig

void GetConfig(COMMCONFIG& config)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommConfig SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetDefaultConfig

static void GetDefaultConfig(int nPort, COMMCONFIG& config)
    throw( CSerialException );

Remarks

Simple wrapper for the GetDefaultCommConfig SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::SetConfig

void SetConfig(COMMCONFIG& config)
    throw( CSerialException );

Remarks

Simple wrapper for the SetCommConfig SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::SetDefaultConfig

static void SetDefaultConfig(int nPort, COMMCONFIG& config)
    throw( CSerialException );

Remarks

Simple wrapper for the SetDefaultCommConfig SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::ClearBreak

void ClearBreak()
    throw( CSerialException );

Remarks

Simple wrapper for the ClearCommBreak SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::SetBreak

void SetBreak()
    throw( CSerialException );

Remarks

Simple wrapper for the SetCommBreak SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::ClearError

void ClearError(DWORD& dwErrors)
    throw( CSerialException );

Remarks

Simple wrapper for the ClearCommError SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetStatus

void GetStatus(COMMSTAT& stat)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommStatus SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetState

void GetState(DCB& dcb)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommState SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::SetState

void SetState(DCB& dcb)
    throw( CSerialException );

Remarks

Simple wrapper for the SetCommState SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::Escape

void Escape(DWORD dwFunc)
    throw( CSerialException );

Remarks

Simple wrapper for the EscapeCommFunction SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::ClearDTR

void ClearDTR()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant CLRDTR which lowers the DTR line.

CSerialPort::ClearRTS

void ClearRTS()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant CLRRTS which lowers the RTS line.

CSerialPort::SetDTR

void SetDTR()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant SETDTR which raises the DTR line.

CSerialPort::SetRTS

void SetRTS()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant SETRTS which raises the RTS line.

CSerialPort::SetXOFF

void SetXOFF()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant SETXOFF which causes transmission to act as if an XOFF character has been received..

CSerialPort::SetXON

void SetXON()
    throw( CSerialException );

Remarks

Calls the Escape function using the constant SETXON which causes transmission to act as if an XON character has been received..

CSerialPort::GetProperties

void GetProperties(COMMPROP& properties)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommProperties SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetModemStatus

void GetModemStatus(DWORD& dwModemStatus)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommModemStatus SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::SetTimeouts

void SetTimeouts(COMMTIMEOUTS& timeouts)
    throw( CSerialException );

Remarks

Simple wrapper for the SetCommTimeouts SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetTimeouts

void GetTimeouts(COMMTIMEOUTS& timeouts)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommTimeouts SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::Set0Timeout

void Set0Timeout()
    throw( CSerialException );

Remarks

Configures both send and receive timeouts to be 0. This causes writes to return immediately, and for reads to return with whatever data is waiting in the receive buffer, rather than wait for the specified amount of bytes to arrive.

CSerialPort::Set0WriteTimeout

void Set0WriteTimeout()
    throw( CSerialException );

Remarks

Configures the send timeouts to be 0. This cause writes to return immediately.

CSerialPort::Set0ReadTimeout

void Set0ReadTimeout()
    throw( CSerialException );

Remarks

Configure the receive timeout to be 0. This causes reads to return with whatever data is waiting in the receive buffer rather than wait for the specified amount of bytes to arrive.

CSerialPort::SetMask

void SetMask(DWORD dwMask)
    throw( CSerialException );

Remarks

Simple wrapper for the SetCommMask SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::GetMask

void GetMask(DWORD& dwMask)
    throw( CSerialException );

Remarks

Simple wrapper for the GetCommMask SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::WaitEvent

void WaitEvent(DWORD& dwMask)
void WaitEvent(DWORD& dwMask, OVERLAPPED& overlapped)
    throw( CSerialException );

Remarks

Simple wrapper for the WaitCommEvent SDK function call. The second version of WaitEvent is the overlapped version which will return immediately and you can wait for the manual reset event member of the OVERLAPPED structure to become signaled in your code. See the Win32 SDK documentation for further details.

CSerialPort::Flush

void Flush()
    throw( CSerialException );

Remarks

Simple wrapper for the FlushFileBuffers SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::Purge

void Purge(DWORD dwFlags)
    throw( CSerialException );

Remarks

Simple wrapper for the PurgeComm SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::TerminateOutstandingWrites

void TerminateOutstandingWrites()
    throw( CSerialException );

Remarks

Calls the Purge function using the constant PURGE_TXABORT which terminates all outstanding write operations and returns immediately, even if the write operations have not been completed.

CSerialPort::TerminateOutstandingReads

void TerminateOutstandingReads()
    throw( CSerialException );

Remarks

Calls the Purge function using the constant PURGE_RXABORT which terminates all outstanding read operations and returns immediately, even if the read operations have not been completed.

CSerialPort::ClearWriteBuffer

void ClearWriteBuffer()
    throw( CSerialException );

Remarks

Calls the Purge function using the constant PURGE_TXCLEAR which clears the output buffer (if the device driver has one)..

CSerialPort::ClearReadBuffer

void ClearReadBuffer()
    throw( CSerialException );

Remarks

Calls the Purge function using the constant PURGE_RXCLEAR which clears the input buffer (if the device driver has one)..

CSerialPort::Setup

void Setup(DWORD dwInQueue, DWORD dwOutQueue)
    throw( CSerialException );

Remarks

Simple wrapper for the SetupComm SDK function call. See the Win32 SDK documentation for further details.

CSerialPort::OnCompletion

virtual void OnCompletion(DWORD dwErrorCode, 
           DWORD dwCount, LPOVERLAPPED lpOverlapped);
    throw( CSerialException );

Parameters

  • dwErrorCode - Specifies the I/O completion status. This parameter may be one of the following values:
    Value Meaning
    0 The I/O was successful.
    ERROR_HANDLE_EOF The ReadFileEx function tried to read past the end of the file.
  • dwCount - Specifies the number of bytes transferred. If an error occurs, this parameter is zero.
  • lpOverlapped - Points to the OVERLAPPED structure specified by the asynchronous I/O function.

Remarks

This function is called as the completion routine for any asynchronous calls to WriteEx or ReadEx. In your derived class from CSerialPort, you can override this function to perform your own specific code in reaction to an asynchronous call completion. Don't forget to call the parent version, namely this function CSerialPort::OnCompletion as it handles the cleanup of the memory allocated for the lpOverlapped parameter.

Planned Enhancements

  • Provide a better sample app. At the moment, it's very much a test program which tests all of the functions.
  • If you have any other suggested improvements, please let me know so that I can incorporate them into the next release.

Contacting the Author

Please send any comments or bug reports to me via email. For any updates to this article, check my site here.

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

PJ Naughter

United States United States
No Biography provided

Comments and Discussions

 
GeneralMy vote of 2 Pinmemberxumenghua26-Sep-12 18:00 
GeneralHOW to download it? PinmemberMember 14106041-May-12 16:14 
QuestionI have two problems to solve with this... Pinmemberdavidjaybrown16-Dec-11 9:52 
GeneralSend large file PinmemberMember 67473684-May-11 19:46 
GeneralCompilling errors in VC6. Pinmemberclwk16-Nov-09 22:01 
GeneralRe: Compilling errors in VC6. Pinmemberclwk16-Nov-09 22:03 
I try to build it in a dll for serial port operation, and met the errors when compiling under vc6.
GeneralThank you Pinmembersandeep.ym3-Jun-09 23:35 
Generalthanks Pinmembershetty25801-Apr-09 22:52 
GeneralRead problem PinmemberEd Shober20-Mar-08 14:07 
GeneralRe: Read problem Pinmemberwct2-Jan-09 4:20 
GeneralTimeouts Pinmemberbbrehm652513-Nov-07 1:21 
GeneralRe: Timeouts Pinmemberbbrehm652513-Nov-07 18:01 
AnswerRe: Timeouts Pinmemberpjnaughter17-Nov-07 5:35 
QuestionTrying to setup an external modem using this lib. Pinmembersamchuan4-Sep-07 22:49 
GeneralCompiling Problems, Please HELP Pinmemberseap42-Aug-07 3:16 
AnswerRe: Compiling Problems, Please HELP Pinmemberpjnaughter17-Nov-07 5:37 
GeneralPerfect Work! Pinmemberbasskeeper7-Jul-07 2:33 
Questioncall a remote phone number with serial IO Pinmemberlarrykind11-Mar-07 6:53 
QuestionReading and Writing continuously at the same port [modified] Pinmembersagar_kjse12-Oct-06 9:32 
AnswerRe: Reading and Writing continuously at the same port Pinmemberpjnaughter8-Nov-06 6:04 
QuestionInterrupt??? PinmemberBraski7-Sep-06 22:06 
AnswerRe: Interrupt??? Pinmemberpjnaughter8-Nov-06 6:11 
Questionstrsafe.h PinmemberBraski6-Sep-06 22:16 
AnswerRe: strsafe.h Pinmemberpjnaughter8-Nov-06 6:12 
GeneralProblem with Microsoft VC++ 6.0 [modified] Pinmemberdaviderave26-Jul-06 21:29 
GeneralRe: Problem with Microsoft VC++ 6.0 Pinmemberpjnaughter8-Nov-06 6:13 
GeneralRe: Problem with Microsoft VC++ 6.0 PinmemberDunchess18-Nov-06 14:03 
AnswerRe: Problem with Microsoft VC++ 6.0 Pinmemberpjnaughter19-Nov-06 4:15 
Generalmultiple ports Pinmemberpicazo18-Feb-06 11:43 
GeneralRe: multiple ports Pinmemberpjnaughter13-Apr-06 6:54 
GeneralNon-Overlapped I/O Pinmemberkissmoses26-Dec-05 17:31 
Generalrs-232 interface Pinmemberszakaryan28-Jun-05 14:08 
GeneralRTS issue PinmemberAlexander A.28-Mar-05 21:26 
GeneralRe: RTS issue Pinmemberpjnaughter28-Mar-05 22:49 
GeneralInvalid access to memory location. PinmemberRFID Chris17-Feb-05 13:29 
QuestionHow to configure baudrate 230400 bps Pinmemberphi-pink14-Feb-05 16:05 
AnswerRe: How to configure baudrate 230400 bps Pinmemberpjnaughter16-Feb-05 2:06 
GeneralRe: How to configure baudrate 230400 bps PinmemberLaunchpad2-May-07 5:00 
GeneralRe: How to configure baudrate 230400 bps Pinmemberpjnaughter2-May-07 5:20 
Generalzmodem/xmodem transfers PinmemberTornSoul22-Jan-05 17:48 
GeneralRe: zmodem/xmodem transfers Pinmemberpjnaughter23-Jan-05 0:46 
GeneralRe: zmodem/xmodem transfers PinmemberTornSoul23-Jan-05 6:20 
GeneralRe: zmodem/xmodem transfers Pinmemberpjnaughter8-Nov-06 6:15 
General"the handle is invalid" message Pinmembergonzul26-Dec-04 2:14 
GeneralCant use from second .h PinsussAnonymous13-Dec-04 1:33 
GeneralRe: Cant use from second .h Pinmemberpjnaughter13-Dec-04 3:40 
GeneralRe: Cant use from second .h PinsussAnonymous13-Dec-04 5:49 
GeneralRe: Cant use from second .h Pinmemberpjnaughter13-Dec-04 6:47 
GeneralRe: Cant use from second .h PinsussAnonymous14-Dec-04 3:45 
GeneralRe: Cant use from second .h Pinmemberpjnaughter14-Dec-04 9:35 

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