Read and parse continuous serial stream

Question

I'm trying to read in and parse a message in the form of X123987 continuously streaming into a serial port. There are no new lines or control characters other than the X which marks the beginning/end of the message. The message contains two, three-character components, ex: 123, and 987. I'm trying to copy bytes as their read into a char array, and then on the control character, return the result, but while this compiles, I don't get any output, and it crashes constantly.

#include <SoftwareSerial.h>

SoftwareSerial RS485Serial(10, 11);

char _byte_received;
char _buffer[10];
char _value[10];

bool OnReceive() 
{
  if (RS485Serial.available()) 
   {
    digitalWrite(13, HIGH);
      _byte_received = RS485Serial.read();
      if (_byte_received == 'X') {
        strcpy(_value, _buffer);
        memset(_buffer, 0, 10);
        return true;
      } else {
        strcat(_buffer, _byte_received);
        return false;
      }
    digitalWrite(13, LOW);
   } else {
    return false;
   }
}
void setup() {
  Serial.begin(9600);
  Serial.println("Restarting...");
  pinMode(13, OUTPUT);   
  pinMode(3, OUTPUT);    
  digitalWrite(3, LOW);  
  RS485Serial.begin(9600);
}

void loop() 
{
  if (OnReceive())
  {
    Serial.print("value: "); 
    Serial.write(_value); 
    Serial.println("");
  }
}

Output:

Restarting...
value: 
Restarting...
value: 
Restarting...
value: 
Restarting...
value: 
Restarting...
value:

I expect to see value: 123987

You wrote: “while this compiles [...]”. No. The code you posted does not compile. — Edgar Bonet
– Edgar Bonet, Commented Jul 20, 2017 at 18:08
I don't know what library are you using, but strcat take two strings, and you are passing a string a char, which is not what you want. concat may be? — user31481
– user31481, Commented Jul 20, 2017 at 18:11
I updated the code to make it complete so it now does actually compile. I'm very likely using the char array functions wrong, and that's probably my issue. Should I creating a one char string before using strcat? I think I just don't know how to ask my question properly. — waspinator
– waspinator, Commented Jul 20, 2017 at 18:47
Look at the prototype for strcat: char *strcat(char *dest, const char *src );. You are trying to pass a char where there should be a char * for the 2nd parameter. — 001
– 001, Commented Jul 20, 2017 at 18:53
How much data will be received ? What else is the sketch doing ? The SoftwareSerial takes over the Arduino, and there is not a lot that the Arduino can do any more. The words "continuously streaming" and "SoftwareSerial" rings an alarm bell. You might need an other Arduino board. — Jot
– Jot, Commented Jul 21, 2017 at 2:12

score 1 · Accepted Answer · 2017-07-20 19:02:36Z

In OnReceive, you are concatening a string with a char. This may be the cause of the resets.

As a side note, you don't really need to use strcat, strcpy and other str functions. You can make your sketch lean by accesing the arrays directly, like this:

char _buffer[10];
int index = 0;

bool OnReceive()
{
  bool status = false;
  if (RS485Serial.available())
  {
    digitalWrite(Pin13LED, HIGH);
    char _byte_received = RS485Serial.read();
    if (_byte_received == 'X') {
      _buffer[index] = 0; // Mark the end of string.
      index = 0;
      status = true;
    } else {
      _buffer[index++] = _byte_received;
      // ToDo: check for overflow;
    }
    digitalWrite(Pin13LED, LOW);
  }

  return status;
}
void setup() {
  Serial.begin(9600);
  Serial.println("Restarting...");
  pinMode(Pin13LED, OUTPUT);
  pinMode(SSerialTxControl, OUTPUT);
  digitalWrite(SSerialTxControl, RS485Receive);
  RS485Serial.begin(9600);
}

void loop()
{
  if (OnReceive())
  {
    Serial.print("value: ");
    Serial.print(_bufer);
    Serial.println("");
  }

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