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.

Quote:

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Originally Posted by Saad Rafey

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.

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;
}

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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()

@Elkvis thanks for your help