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Error while reading data from serial port

This is a discussion on Error while reading data from serial port within the Windows Programming forums, part of the Platform Specific Boards category; I am writing a program in Visual C++ to access serial port.Code is given below:- Code: #include "stdafx.h" #include <windows.h> ...

  1. #1
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    Feb 2013
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    Error while reading data from serial port

    I am writing a program in Visual C++ to access serial port.Code is given below:-


    Code:
        #include "stdafx.h"
        #include <windows.h>
        #include <stdlib.h>
        #include <stdio.h>
        #include <string.h>
        #include <commdlg.h>
    
    
        int nread,nwrite;
    
    
    
    
        void main()
        {
    
    
         COMMTIMEOUTS timeouts;
         COMMCONFIG dcbSerialParams;
         char *words,*buffRead, *buffWrite;
         DWORD dwBytesWritten,dwBytesRead;
    
    
    
    
    
    
         HANDLE hSerial= CreateFile(L"COM1", GENERIC_READ | GENERIC_WRITE,
                               0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
         if ( hSerial == INVALID_HANDLE_VALUE) 
         {
         if (GetLastError() == ERROR_FILE_NOT_FOUND)
         {
         printf(" serial port does not exist \n");
         }
         printf(" some other error occured. Inform user.\n");
         }
    
    
    
    
         //DCB     dcbSerialParams ;
         //GetCommState( hSerial, &dcbSerialParams.dcb);
         if (!GetCommState(hSerial, &dcbSerialParams.dcb)) 
         {
         printf("error getting state \n");
         }
    
    
         dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb);
    
    
    
    
         dcbSerialParams.dcb.BaudRate = CBR_1200;
         dcbSerialParams.dcb.ByteSize = 8;
         dcbSerialParams.dcb.StopBits = ONESTOPBIT;
         dcbSerialParams.dcb.Parity = NOPARITY;
    
    
         dcbSerialParams.dcb.fBinary = TRUE;
         dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_DISABLE;
         dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_DISABLE;
         dcbSerialParams.dcb.fOutxCtsFlow = FALSE;
         dcbSerialParams.dcb.fOutxDsrFlow = FALSE;
         dcbSerialParams.dcb.fDsrSensitivity= FALSE;
         dcbSerialParams.dcb.fAbortOnError = TRUE;
    
    
    
    
        if (!SetCommState(hSerial, &dcbSerialParams.dcb)) 
        {
        printf(" error setting serial port state \n");
        }
    
    
    
    
        GetCommTimeouts(hSerial,&timeouts);
    
    
        timeouts.ReadIntervalTimeout = 1000;
        timeouts.ReadTotalTimeoutConstant = 1000;
        timeouts.ReadTotalTimeoutMultiplier = 1000;
        timeouts.WriteTotalTimeoutConstant = 1000;
        timeouts.WriteTotalTimeoutMultiplier= 1000;
    
    
        if(!SetCommTimeouts(hSerial, &timeouts)) 
        {
        printf("error setting port state \n");
        }
    
    
    
    
        //****************Write Operation*********************//
        words = "B";
        nwrite = strlen(words);
    
    
        buffWrite = words;
        dwBytesWritten = 0;
    
    
        if (!WriteFile(hSerial, buffWrite, nwrite, &dwBytesWritten, NULL)) 
        { 
        printf("error writing to output buffer \n");
        }
        printf("Data written to write buffer is\n %s \n",buffWrite);
    
    
    
    
    
    
    
    
    
    
        //***************Read Operation******************//
        buffRead = 0;
        dwBytesRead = 0;
        nread = strlen(words);
    
    
        if (!ReadFile(hSerial, buffRead, nread, &dwBytesRead, NULL)) 
        {
        printf("error reading from input buffer \n");
        }
        printf("Data read from read buffer is \n %s \n",buffRead);
    
    
        CloseHandle(hSerial);
    
    
        }
    Above program is working properly while write operation (i.e writing data on serial port) but while read operation its is not reading data from serial port.


    I am getting output on console window is given below:-
    Code:
        Data written to write buffer is
        B
        error reading from input buffer
        Data read from read buffer is
        <null>
    I want to know where I am getting wrong and how to resolve it.

  2. #2
    Registered User
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    2,348
    Quote Originally Posted by Saad Rafey View Post
    Code:
    void main()
    this is the first mistake that immediately stood out to me. the correct form is

    Code:
    int main()
    
    or
    
    int main(int argc, char** argv)
    the second mistake you made was posting C code in the C++ forum. an alternative to this would be to post in the windows forum, as you are clearly using windows-specific system calls.

  3. #3
    and the hat of wrongness Salem's Avatar
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    First of all, your indentation is poor.
    Code:
    #include "stdafx.h"
    #include <windows.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include <commdlg.h>
    
    //!! why are these global?
    int nread, nwrite;
    
    int main()  //!! main returns int - not void!
    {
      COMMTIMEOUTS timeouts;
      COMMCONFIG dcbSerialParams;
      char *words, *buffRead, *buffWrite;
      DWORD dwBytesWritten, dwBytesRead;
    
      //!! http://msdn.microsoft.com/en-us/library/c426s321%28v=vs.80%29.aspx
      //!! Use _T("COM1") then your code will still compile and work
      //!! if you switch between ANSI and UNICODE
      HANDLE hSerial = CreateFile(L"COM1", GENERIC_READ | GENERIC_WRITE,
                                  0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
      if (hSerial == INVALID_HANDLE_VALUE) {
        if (GetLastError() == ERROR_FILE_NOT_FOUND) {
          printf(" serial port does not exist \n");
        }
        printf(" some other error occured. Inform user.\n");
      }
    
      //DCB     dcbSerialParams ;
      //GetCommState( hSerial, &dcbSerialParams.dcb);
      if (!GetCommState(hSerial, &dcbSerialParams.dcb)) {
        printf("error getting state \n");
      }
    
      dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb);
      dcbSerialParams.dcb.BaudRate = CBR_1200;
      dcbSerialParams.dcb.ByteSize = 8;
      dcbSerialParams.dcb.StopBits = ONESTOPBIT;
      dcbSerialParams.dcb.Parity = NOPARITY;
      dcbSerialParams.dcb.fBinary = TRUE;
      dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_DISABLE;
      dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_DISABLE;
      dcbSerialParams.dcb.fOutxCtsFlow = FALSE;
      dcbSerialParams.dcb.fOutxDsrFlow = FALSE;
      dcbSerialParams.dcb.fDsrSensitivity = FALSE;
      dcbSerialParams.dcb.fAbortOnError = TRUE;
    
      if (!SetCommState(hSerial, &dcbSerialParams.dcb)) {
        printf(" error setting serial port state \n");
      }
    
      GetCommTimeouts(hSerial, &timeouts);
      timeouts.ReadIntervalTimeout = 1000;
      timeouts.ReadTotalTimeoutConstant = 1000;
      timeouts.ReadTotalTimeoutMultiplier = 1000;
      timeouts.WriteTotalTimeoutConstant = 1000;
      timeouts.WriteTotalTimeoutMultiplier = 1000;
    
      if (!SetCommTimeouts(hSerial, &timeouts)) {
        printf("error setting port state \n");
      }
    
    
      //****************Write Operation*********************//
      words = "B";
      nwrite = strlen(words);
      buffWrite = words;
      dwBytesWritten = 0;
      if (!WriteFile(hSerial, buffWrite, nwrite, &dwBytesWritten, NULL)) {
        printf("error writing to output buffer \n");
      }
      printf("Data written to write buffer is\n %s \n", buffWrite);
    
      //***************Read Operation******************//
      buffRead = 0;
      dwBytesRead = 0;
      nread = strlen(words);  //!! see the words
      if (!ReadFile(hSerial, buffRead, nread, &dwBytesRead, NULL)) {
        printf("error reading from input buffer \n");
      }
      printf("Data read from read buffer is \n %s \n", buffRead);
    
      CloseHandle(hSerial);
    
      //!! all done successfully
      return 0;
    }
    1. Pay attention to all the other //!! comments in the code.

    2. The reason for the crash is as follows - you're not pointing to a buffer you can write to.
    buffRead is a NULL pointer!

    Try something like
    char buffRead[100];
    nread = sizeof(buffRead); // note, not strlen()
    stahta01 likes this.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  4. #4
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    Feb 2013
    Posts
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    @Elkvis thanks for your help

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