ExtraTasks.md

---

title: "Libaries and Inheritance" author: "Dan Goldsmith"

Libaries

Libaries

• Allow us to reuse code in multiple projects.
  • Write the Code once
  • Include the Libary to use it.

Example: Turning the Class into a Library

• Now we have gone to all the effort of creating our class.
• We should make it so it is usable by other programs.
• Break the code out into new files, which can be included.
• NOTE: WE cannot do this in the simulator.

Turning the code into a library

• We need two files here.
  • Headerfile contains the definitions
  • Source file contains the code to make things work

Libary: Header file (Flasher.h)

\scriptsize

#ifndef CUSTOM_FLASHER.H
#define CUSTOM_FLASHER.H

#include "mbed.h"

class Flasher{
    private:
        float delay;
        DigitalOut pin;
        
  public:
     //Constructor
     Flasher(PinName thePin, float delayTime);

	void flash(int times); 
};
endif

Library Source file (Flasher.c)

\scriptsize

#include "Flasher.h"
#include "mbed.h"

//Constructor
Flasher(PinName thePin, float delayTime) : pin(thePin) {
    delay = delayTime;
}

void flash(int times){
    for (int x = 0; x< times; x++){
		pin= !pin;
		wait(delay);
	}
}

Main Program Code

\scriptsize

#include "mbed.h"
#include "Flasher.h"

int main() {
	//Setup
	Flasher ledOne = Flasher(LED1, 0.5)
	Flasher ledTwo = Flasher(LED2, 0.25)
	
	//Loop
	while(1){
		ledOne.flash(5);
		ledTwo.flash(10);
	}

Inheritance

Inheritance Example: A new type of Flasher.

• Lets build on the previous Flasher Example.
  • Number of times the sequence happens based on some "State".
  • This time we have multiple LED's
  • Different types of Flasher will show different sequences.

UML Class Diagrams Inheritance

• What are our attributes?
  • LED's that are attached.
  • State the flasher object is in.
• What are the functions
  • Flashing Sequence.
  • Alternate Flashing Sequence

C++ Inheritance Implementation: Base Class

\scriptsize

class BaseFlasher{
    private:
        int state = 0; //Initialise the state variable
        float delay; 
        
    public:
        //Constructor
        BaseFlasher(float delayTime) {
            delay = delayTime;
	    }

        //Run a sequence of flashes
	    void flash(int times){
	        for (int x=0; x < times; x++){
	            doFlash(); //Update the lights
	        }
	    }		
		//Note.  Needs to be virtual otherwise we inherit the parent version.
		virtual void doFlash();  //Actually toggle the lights
};

C++ Inheritance Implementation: Subclass

\scriptsize

class OneLedFlasher : public BaseFlasher{
    public:
            DigitalOut theLED; //Class Only Variable for the LED    
    
        OneLedFlasher(float delayTime, PinName thePin) 
		  : BaseFlasher(delayTime),  theLED(thePin)  {
            //Nothing needs to go here.
        }   
        
        void doFlash() //Polymorphic
        {
            theLED = !theLED;
        }
		
		void alternateFlash()
		{
			for (int x=0; x< times; x++){
				theLED = !=theLED;
				wait(0.1);
				theLED = != theLED;
				wait(0.9);
	    }
};