Question

I am having a problem with a Serial Port communication between Arduino Nano and C++, even though the problem is in C++ side. Basically I want to send integers (or long,…) from the Arduino to a C++ program to be processed.

First I did a test sending information from the Arduino to the computer using Matlab. The Arduino code is pretty simple:

int i = 0;

void setup() {

   // start serial port at 9600 bps:
   Serial.begin(9600);
   establishContact(); 
}

void loop() {
  Serial.println(i);
  i=i+1;  
  delay(10);
}

void establishContact() {
   while (Serial.available() <= 0) {
     Serial.println('A', BYTE);
     delay(10);
   }
}

The Matlab side is also simple:

clc;
clear all;
numSec=2;
t=[];
v=[];

s1 = serial('COM3');    % define serial port
s1.BaudRate=9600;               % define baud rate
set(s1, 'terminator', 'LF');    % define the terminator for println
fopen(s1);

try                             % use try catch to ensure fclose
                                % signal the arduino to start collection
    w=fscanf(s1,'%s');              % must define the input % d or %s, etc.
    if (w=='A')
        display(['Collecting data']);
        fprintf(s1,'%s\n','A');     % establishContact just wants 
                                    % something in the buffer
    end

    i=0;
    t0=tic;
    while (toc(t0)<=numSec)
        i=i+1;
        t(i)=toc(t0);
        t(i)=t(i)-t(1);
        v(i)=fscanf(s1,'%d');     
    end

    fclose(s1);
    plot(t,v,'*r')   

catch me
    fclose(s1);                
end       

My goal is, with C++, do the same that is done in Matlab using fscanf(s1, ‘%d’).

Here is the current code that I am using (C++ code):

void main()
{
 HANDLE hSerial;
 hSerial = CreateFile(TEXT("COM3"), 
   GENERIC_READ | GENERIC_WRITE, 
   0,
   NULL, 
   OPEN_EXISTING,
   FILE_ATTRIBUTE_NORMAL,//FILE_FLAG_OVERLAPPED, 
   NULL);



if ( hSerial == INVALID_HANDLE_VALUE)
 {
  printf("Error initializing handler");
 } 
 else 
 {

  // Set the parameters of the handler to the serial port.
  DCB dcb = {0};

  dcb.DCBlength = sizeof(dcb);

  if ( !GetCommState(hSerial, &dcb) )
  {
   printf("Error setting parameters");
  }

  FillMemory(&dcb, sizeof(dcb), 0);
  dcb.BaudRate = CBR_9600;
  dcb.ByteSize = 8;
  dcb.StopBits = ONESTOPBIT;
  dcb.Parity = NOPARITY;

  if ( !SetCommState(hSerial, &dcb) )
  {
   // error setting serial port state.
  }

  // Tell the program not to wait for data to show up
  COMMTIMEOUTS timeouts = {0};

  timeouts.ReadIntervalTimeout = 0;//20;
  timeouts.ReadTotalTimeoutConstant = 0;//20;
  timeouts.ReadTotalTimeoutMultiplier = 0;//50;
  timeouts.WriteTotalTimeoutConstant = 0;//100;
  timeouts.WriteTotalTimeoutMultiplier = 0;//100;

  if ( !SetCommTimeouts(hSerial, &timeouts) )
  {
   printf("Error setting the timeouts");

  }

  char szBuff[5] = "";
  DWORD dwBytesRead = 0;
  int i = 0;
  char test[] = "B\n";
  int maxSamples = 10;
  DWORD dwCommStatus;

  WriteFile(hSerial, test, 2, &dwBytesRead, NULL);

  SetCommMask(hSerial,EV_RXCHAR);

  while (i < maxSamples)
  {
   WaitCommEvent (hSerial, &dwCommStatus, 0);

   if (dwCommStatus & EV_RXCHAR) 
   {
    memset(szBuff,0,sizeof(szBuff));
    ReadFile(hSerial, LPVOID(szBuff), 4, &dwBytesRead, NULL);

    cout<<szBuff;
    printf(" - %d - \n", atoi(szBuff));
   }
   i++;     
  }

  scanf("%d", &i);

  CloseHandle(hSerial);
 }
    }

The goal of my code would be something like num = ReadSerialCOM(hSerial, "%d");

My current C++ code reads the information from the buffer, but there is not an accepted end of line, which implies that my numbers (integers) are received cut.

Eg:

I send 8889 from the Arduino, which places it in the COM port. And the command ReadFile saves ’88’ into szBuff. At the next iteration ’89\n’ is saved into sZBuff. Basically I want to avoid to post-process sZBuff to concat ’88’ and ’89\n’.

Anyone?
Thanks!

Answer 1

As Hans Passant and dauphic pointed, it doesn’t seem to be a general solution for my question. I am writing, though, the code that I was trying to avoid, just in case somebody finds it useful or face the same problem that I had:

int i = 0;  
DWORD dwBytesRead = 0;
DWORD dwCommStatus = 0;
char szBuff[2] = "";                
int maxRead = 20;   
int sizeNum = 1;    
int *num    = (int*)malloc(maxRead*sizeof(int)); 
char *currNum;
char *pastNum;

// Write something into the Serial Port to start receive 
// information from the Arduino
WriteFile(hSerial, (LPCVOID)"A\0", 1, &dwBytesRead, NULL);    
SetCommMask(hSerial, EV_RXCHAR);

// Start reading from the Serial Port
while ( i < maxRead )
{
    WaitCommEvent (hSerial, &dwCommStatus, 0);

    if (dwCommStatus & EV_RXCHAR) // if a char is received in the serial port
    {
        ReadFile(hSerial, LPVOID(szBuff), 1, &dwBytesRead, NULL);

        if ( szBuff[0] > 47 && szBuff[0] < 58 )
        {
            sizeNum++;
            if (sizeNum ==2)
            {
                currNum = (char*)malloc(sizeNum*sizeof(char));
                strcpy(currNum, szBuff);
            } else
            {
                if (pastNum != NULL)
                    free(pastNum);
                pastNum = currNum;
                currNum = (char*)malloc(sizeNum*sizeof(char));
                strcpy(currNum, pastNum);
                strcpy(currNum+(sizeNum-2)*sizeof(char), szBuff);
            }

            cout << szBuff<<endl;   
        } else if (szBuff[0] == '\n' && sizeNum > 1) // end of number
        {
            num[i] = atoi(currNum);
            i++;                    

            sizeNum = 1;
            if (currNum!=NULL)
                free(currNum);
        }
    }
}