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OK.

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Welcome back to a another lesson on inheritance in this lesson, I am going to be kind of extending

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what we talked about before and adding one or two new things to our knowledge base about inheritance.

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It's going to be kind of a short lecture x.

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I'm only going to go over these few things, but definitely pay attention because they will be important.

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So what we're going to go over is how the constructors and D structures work in inheritance.

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As in like, when is which constructor called?

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And we're also going to go over this thing that we talked about, which I said you couldn't ignore in

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the last lecture because I just wanted you to know that you could use this for inheritance, but this

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word right here can be changed from public to other words as well.

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And we're going to talk about this base class access specification, which is what this is right here

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and how it relates to the base class and the difference between that and this right here.

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Because remember, this used to be private at some point and we changed it to protect it so we could

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have access inside of this friend.

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Function, right, are overloaded upstream operator and we wanted access to the private members assist

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declared in Karjat.

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Eight.

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It is a protected member.

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Protected means that we have access to these in the base class.

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These members inside of the derived classes rightly derive classes have access to these now if we put

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protected.

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So the point is, though, is that we're going to talk about this access, specify a lot and what it

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means if we change it.

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So first off, we're going to talk about the constructors and D structures, though.

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So in each class, in each derive class and base class, I have added a destructor.

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And I have put a printout line in the destructor saying that we are in it, so we are in the sedan destructor.

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I'm doing that for each destructor and I put a little sea out in the constructor as well.

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So constructor and destructor, I have little printout statements that will tell us that we are in there,

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so we'll know when it's called.

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And I did that for the base class and all of the drive classes.

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So what I'm going to do is go ahead and run this program now, but I'm not going to print out info about

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the cars using the overloaded operator because that will create unnecessary clutter.

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What we want to do is just kind of see the printouts and know what order the constructors are called

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in and what order the structures are called in in terms of the base class versus the derived class.

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So let's go ahead and run this and we will see what the output is.

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OK, so let's go ahead and zoom in on this a little bit.

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I'm going to scroll up a bit, so we see that we are first in the car constructor and then we are in

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the truck constructor, then car, then sedan, then car, then SUV.

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So notice that we instantiate our objects in this order truck and then sit in an SUV.

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So what happens with the constructor in inheritance is that the base class constructor will be called

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first before the derived class constructor.

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So you notice we instantiate a truck, right?

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So what C++ needs to do is it needs to sees that you instantiate a truck and then it needs to look at

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the superclass or base class of truck, which is car, right?

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So it goes to car called the car constructor.

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Then it comes back and does the truck constructor.

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When we do a sedan, it has to repeat the same process over.

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It says, OK, what's the superclass of sedan with the car?

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I go to a car called Car Constructor, then calls a day and it does the same thing for SUV.

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You see car and then SUV.

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The destructor is the mirror image of this right here.

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It's basically inverted, so you notice that it destroys the most recently created derived class object.

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So SUV and then it goes to the car, right?

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And then the sedan and then car and truck and then car.

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So the whole ordering is reversed in terms of this and also it is reversed in terms of whether the base

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class or drive class is called first.

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So the derived class destructor is called before the base class destructor opposite of the constructor,

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where the base class constructor is called before the derived class constructor.

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So you can just see that it happens in this order, and then it's just a mirror image right here.

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So this part right here is the inverse of the constructor up here as far as ordering.

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So just wanted to show you that because it's kind of important to know what's going on and what's happening

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and what order.

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So the next thing that I want to talk to you about is this base class access specification keyword here.

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So right now we have public.

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So what this word really means is it describes how the.

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Functions here and members and everything are going to be inherited into the derived class.

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So since we say public.

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That means that all of these methods here.

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Sorry, all of these member functions here, I keep calling them methods because that's a way to refer

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to them in other programming languages.

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All of these member functions here are going to be inherited into Sudan and they are going to be made

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accessible.

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To Maine, for example, from Sudan as public member functions, so.

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It says, you know, these are public right here.

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It's that means that what's going to happen when we inherit this as public, it's going to make those

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functions public through the sedan class as well.

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So imagine that we just take all this highlighted stuff here and we just copy paste it here into this

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public section.

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That's basically what's happening.

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It means that all of these highlighted member functions here are going to become public in Sudan and

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so we can use them in Maine.

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What I can do is change this if I change this to protected.

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What happens is that you notice that there was a protected word right here, right, and that gave us

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access to these inside of the derived classes, right?

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All the derived classes.

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If I put a protected.

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Right here, what it means is that it's going to when we copy all of this and like invisibly make it

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available here.

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In our sedan class, it's not going to be public anymore.

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These are not going to be public anymore when they're here in sedan.

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They're going to be protected in what is protected.

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Mean again, it means that they're only available to classes that derive from the classes as protected.

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So if we had another class that was deriving from sedan as a sedan was the super class, then that means

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that the protected car.

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Member functions here would be available to that class that was deriving from it.

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But the problem is is it's not available elsewhere in the client code.

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Watch what happens when I go to Maine.

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Immediately, these two methods coming from car, right, set fuel and set paint are actually coming

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from car.

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You see set fuel and step paint.

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They're red now because we cannot access them in Maine because they are protected.

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They are only available to whatever classes may derive from Sudan because they're being exposed to this

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client code in a protected manner, in a public manner.

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If I go right here, it says that fuel is a protected member of car member of car that's just telling

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us that we cannot access that from here in Maine.

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But notice how swetnam doors is still fine.

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Why is that?

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Because we put Satnam Dawes is actually a member of Sudan.

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It's not a member of car.

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And what did we say about the members of Sudan?

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We said that their public right here, right?

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That's why this is accessible in Maine.

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Yet these set feelings that paint are not accessible in Maine.

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Why?

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Because they are protected.

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We said protected car.

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So now when we grab all this, these are all protected, they're not available to me.

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That's why when we tried to call those functions here in Maine, set fuel, set paint, they are actually

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not available to me.

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So we would want to leave this as public, right?

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We put it back to public.

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You notice that these disappear.

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So there is one more thing to do, and that is private.

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And it's the same thing is protected, except rather than exposing the inherited member functions here

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as protected, it's now exposing them as private so they're not available either in Maine.

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So if I go here now, it says Fairfield is a private member of CAR.

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So that means that it's private, constrained by private inheritance here, and I click there, and

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it brings us to here and it's just like, Hey, you made it private, you made everything that we're

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inheriting from car all private, so it is inaccessible to any client code.

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So that's just something to note, that's what the access specified means, the access, the base class

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access specify air, which is the way that you inherit stuff from the base class.

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Whatever word you put here that you're just describing, the way that it's going to be accessible from

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Sudan.

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So remember, protected one might be nice if you're wanting to make another derived class of Sudan,

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where Sudan is like a super class and now you have multiple levels of inheritance.

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That way, you would expose all of car to that like derived class of Sudan in a protected manner, so

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you could use it in that derived class from Sudan.

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Public will make stuff from car

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be accessible to client code just like these are.

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I mean, these are public, right?

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So if you're like, well, I'm also going to want in my client code to call all of cars member functions

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here, then you need to make this public.

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All right.

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So that was kind of it for this lesson.

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I just you know what this means and how you can change it.

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You know, if you're using multiple levels of inheritance, then you might be putting protected here.

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And there are some reasons why you might want to put money.

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You might want to put private.

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Maybe you still want to just use some of the methods in here.

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You know, stuff is still stuff is still accessible to car.

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If it's protected, you know, it doesn't, it doesn't matter what you feel like.

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If I put private here, even I could still use stuff from car in sedan.

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Right?

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So for example, I can go over here to sedan, even though this is private, you know, this doesn't

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work here anymore.

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But if I go to sedan, let's just put something super random.

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So.

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Let's just say in setting some doors, we also want to just randomly display.

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Let's see, like the odometer or something like that.

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I don't know.

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Let's just say get pain or something like that.

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Like, what if we just want to show you the pain as well?

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And it's like, so whenever you set the number of doors, we just have this thing that's like, uh,

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you know, by the way, the paint color is.

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Like that.

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So what I can do in here is actually use this function in here, get paint.

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So if I go back here, I can say, by the way, the paint color is in, I can just say get paint because

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I have access to this function because it is inherited.

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All right.

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So.

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It's not really saying, like all this stuff is public in terms of my sedan class, when I say private,

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it means that when I'm using these.

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When I copy all these over to Sudan, they become they're basically going to be put down here in this

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private.

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That's what you can imagine.

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Like they're they're basically like put down here in the private list because all of these methods are

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private in terms of the Sudan in which it's saying that I'm exposing these in a private way to the clan

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code.

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So we still have full accessibility to all of this in the Sudan class.

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So no matter what word you put right here, private protected public, you're still going to have access

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to everything here in car because you're inheriting it right?

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If you were to put all of this highlighted junk down here in protected and changes to private or something,

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then they would be private to car and the inheriting class would not have access to it.

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So you notice, like, let's take a look here.

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This is totally fine, right?

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And I can go ahead and test this out.

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I can print it out.

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We'll go back to Maine.

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I've commented this stuff out.

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All right.

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So let's go ahead and run this.

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So you notice this says, by the way, the pink color is white, so you see that right there, right?

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So if I can go if I go back here to car and I was to change this from public to private.

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We start running into a ton of issues, right, if I go back here to Main, you noticed that like none

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of these are accessible, like now, these aren't accessible because they're private members of car.

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And if I go to Sudan, this is red too, because it's a private number of cars.

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So I don't even have access inside of this sedan derived class.

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So that's why these should be public.

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And I just wanted to show you that if you were to change this to private, that makes that changes the

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accessibility inside the derived classes.

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But as far as inheritance, it changes the accessibility as far as anything that wants to get access

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to the sedan, class client code, whoever imports it, like up here, you know, like we have day and

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age.

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That means that the way that we describe the inheritance is kind of what affects the accessibility we

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would have in Maine to some of the methods that got inherited from car, right?

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All of this stuff it now becomes part of sedan is defined at the accessibility level by this word.

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All right, cool.

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So I'm actually going to make this public because I want that to be public, right?

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And I'm going to change this back.

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This makes no sense to have it here, so I get rid of that.

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Cool.

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So now everything you notice will be accessible in here, so if I in peace, they are accessible, and

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that's why I believe that as public in here.

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So that's pretty much all I had to say about those two kind of sub topics.

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It's important to know which order things are being called in as far as inheritance.

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And important to know the different types of access specification that you can do.

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If at some point you end up having multiple levels of inheritance, you'll need to know about protected

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and stuff like that, right?

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Because you may not want to make those members here accessible all the way down to the client.

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Could you maybe just want to have it accessible to a derived class of sedan or truck or SUV, whatever

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you end up trying to implement?

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All right, so with that, I will see you in the next lecture.