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".


class MySerial:public Stream{
        int param;
        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; 


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

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

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

1 Answer 1


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:


#ifndef _MYSERIAL_H_
#define _MYSERIAL_H_

#include <SoftwareSerial.h>

class MySerial: public SoftwareSerial {
  int param;


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

  void resend(char c) {


#include "MySerial.h"

MySerial mySerial(6, 7);

void setup() {

void loop() {
  if (mySerial.available()) {
    int c = mySerial.read();
  • Thanks. I made the indicated changes. I am still troubled with the constructor declaration, for taking a Stream object as initial object.
    – Brethlosze
    Commented Mar 22, 2019 at 15:13
  • Your answers are great just as the last time. I will study this code further.
    – Brethlosze
    Commented Mar 22, 2019 at 16:37

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