Create New Serial Class Inheriting from Stream

Question

How should I inherit from Stream, for creating a new class MySerial able to be initialized from a Stream0 instance?.

The error so far is: "cannot declare variable 'mySerial' to be of abstract type 'MySerial'".

If I make a class MySerial not inheriting, but adding a property Stream, everything works fine, except the new call mechanism for the resend() function, created to accept Stream instances.

EDIT: This is the edited code. Current error is: "expected unqualified-id before '=' token".

MySerial.h

class MySerial:public Stream{
    private:
        int param;
    public:
        MySerial(){}; // OK
        MySerial(Stream &Serial0){MySerial=&Serial0} // Here is the question
        // Stream Implementation
        int available(){return available();}
        int read(){return read();}
        int peek(){return peek();}
        size_t write(uint8_t c){return write(c);}
        using Print::write; 
};

MySerial.ino

#include <MySerial.h>
#include <SoftwareSerial.h>

SoftwareSerial swSerial(6,7);
MySerial mySerial(swSerial);

void setup(){}
void loop(){    
    if (mySerial.available()){
        c=mySerial.read();
        resend(mySerial,c);
    }
}
// This function should accept any Stream: SoftwareSerial, MySerial, Serial...
void resend(Stream &Stream0, char c){
    Stream0.write(c);
}

Juraj · Accepted Answer · 2019-03-22 16:33:53Z

The Stream class has pure virtual methods which must be implemented in derived not abstract class.

The pure virtual method from base class Print is:

virtual size_t write(uint8_t) = 0;

The pure virtual methods from Stream are:

virtual int available() = 0;
virtual int read() = 0;
virtual int peek() = 0;

additionally add in your class the line

using Print::write;

to pull in overloaded methods write(str) and write(buf, size) fromPrint

Here I have an example of a simple class derived from Stream.

EDIT: Most of your question seemed to focus on wrapping some Stream implementation. Now I see that you maybe want to enhance the SoftwareSerial class and add a new method in the inherited class. It is simple:

MySerial.h

#ifndef _MYSERIAL_H_
#define _MYSERIAL_H_

#include <SoftwareSerial.h>

class MySerial: public SoftwareSerial {
private:
  int param;

public:

  MySerial(uint8_t receivePin, uint8_t transmitPin) :
      SoftwareSerial(receivePin, transmitPin, false) {
    param = 0;
  }

  void resend(char c) {
    write(c);
  }
};
#endif

MySerial.ino

#include "MySerial.h"

MySerial mySerial(6, 7);

void setup() {
  mySerial.begin(9600);
}

void loop() {
  if (mySerial.available()) {
    int c = mySerial.read();
    mySerial.resend(c);
  }
}

Thanks. I made the indicated changes. I am still troubled with the constructor declaration, for taking a Stream object as initial object. — Brethlosze
– Brethlosze, Commented Mar 22, 2019 at 15:13
Your answers are great just as the last time. I will study this code further. — Brethlosze
– Brethlosze, Commented Mar 22, 2019 at 16:37

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