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Hello everyone.



2

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So in this we do I want to discuss about friend functions.



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OK so let us take an example suppose I have a class drug now inside the class drug.



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I have some private public and protected properties so private.



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Protected and public.



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OK.



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So let's say x is a private property.



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Why is a predicted property and Z is a public property.



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OK.



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So the private property X it is not accessible outside the truck class.



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Okay.



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Similarly the protected property right.



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It is accessible.



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Our tender truck last but only with the help of derived classes and Z.



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This property is open to all.



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We can access it anywhere.



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Okay.



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Now suppose I have a class bus.



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Now the bus class has a print function okay.



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And this print function it wants to access the private property of the class.



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Okay you want to access the X..



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Okay.



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So how can this print function can access the private property of an entire class.



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Okay.



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So the answer is with the help of friend functions.



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Okay.



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So with the help of a friend functions a class a class can access the private and the protected properties



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of the order class.



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Okay so with the help of friend functions.



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A class can access the private in the protected property of the class because the public properties



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are already accessible to everyone.



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Okay.



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So what we have to do.



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So what we have to do we have to make this print function a friend of this class.



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Okay.



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Now we all know friends knows it don't.



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Okay I want to access the secret off track.



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So the print has to become the friend.



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Okay.



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Different knows the secret.



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So when the brain function will become the friend of the class.



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It can access the secret property it can access all the secrets of the track class.



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Okay.



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In order to see in gold



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okay.



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So I have a class drug now inside the gastric.



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We have decided that I have some I have some private property I have some predicted property and I will



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have some public property



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okay.



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Now I have a class bus class bus has a function



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so class bus has a function now what this function wants this function wants to excess excess the X



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of drug.



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This function was to exist the private and the public properties private and the protected properties



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of the track class.



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Okay so how can we do this.



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So the only ways what we will do we will declare this print function as a friend of the class.



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Okay so what is the syntax syntax is very simple.



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First of all we have to write friend



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then we have to write void then bus scope resolution operator the name of the function print.



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Okay so what will happen now.



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Okay so now the print function of the bus class is now a friend of the class.



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Okay the print function of the bus class is now a friend of the class.



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So this print function now can access all the secrets of the class okay.



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But if it will then this file will get an added okay that it will be at this lane.



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Let's end if I look okay so what is the added



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okay.



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So this will be Z okay.



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So it will then this file we will get an error at this line so what is their ETA is at this line.



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Compiler doesn't know what this bus.



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Okay.



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If you will see that it so bus has not been declared.



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So what happened in C++



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Okay so we are getting a compilation error at this length.



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So what happens in C++.



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So in C++ the execution starts from the mean but the compiler should start from the very first line.



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Okay.



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So the completion will be from top to bottom.



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So at this line line number well we do not have bus.



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Okay buses not declared.



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So compiler will not go at line number 15 it will not search at this land the compiler will stop and



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it will tell us that it doesn't know what is bus.



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Okay.



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So what we have to do we have to declare we have to write this code in front of before the class okay



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above the track class so let's move the whole code



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okay.



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So listen this file



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so at this time we are not getting any added.



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Okay now one more thing that we have to we have to be careful.



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So now this function is a friend of the track class.



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So we cannot give the definition here.



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Okay.



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We cannot give the definition we have to give the definition outside the class.



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Okay.



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So I am given the definition here.



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So for giving the definition the structure will be void bus scope resolution operator print okay.



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So now in this function.



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So now here within this function I can access all the secrets of the class private and protected properties.



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Okay.



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X Y and Z all are accessible.



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Okay.



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So for accessing the private properties and the protected properties first of all we will create an



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object.



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So correctly so I can access X..



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Let's say existing I can access y.



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So do not y as let's say 20 and let us also print the value of x and y so sealed do not X and do not



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v



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okay.



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Now let us call this function brain function.



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So I am creating an object must be and will call the function b dot print



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okay.



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Now listen this file



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so I would produce coming out with 10 and 20.



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Okay so I will code is working fine.



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So our code is working fine okay so let's do one more thing.



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Suppose I have a global function okay.



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So I have a normal global function.



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Let's say the name of the function is best okay.



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Now this test function



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this test function also wants to access the private and the predicted this track.



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It also wants to access the private property of the class.



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Okay.



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So what we have to do we will do the same thing.



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We will make this test function as the friend of the track class.



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Okay.



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So this index will be quite simple.



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We will write friend then void and then test.



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Okay.



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So again if you will then this file we will get the compilation error at this line because this test



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function does not belong to a class because we have written friend in before the test function.



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So this test function doesn't belong to drug class and when we will reach line number it Dean we will



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get compilation error saying that best is not defined okay because test is written below the track class.



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Okay so what we have to do we have to move this code above.



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Okay so what we can do we will write the declaration.



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So this is the declaration okay.



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And here we can write the definition.



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So now we will not get completion at it.



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Okay so.



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Okay.



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So let's copy this code only



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okay.



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So now let us call this function test from the mean.



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Okay so test now let's define



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Okay so 10 20 and again 10 20.



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So the first one is due to by Sprint function.



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The second one is due to the global function which is the friend of the class.



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Okay.



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Okay.



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So one thing to note here is this test and this print function.



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They are not the part of the class.



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Okay.



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They are not the part of the class.



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So.



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So these two functions are not part of class.



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So if I declare another function if I defined another function here let's have white display and inside



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the display function.



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So can I write C out this a can I write this.



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So is this line correct.



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Obviously this is correct.



159

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So what is the meaning of this.



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This may contain the address of the current object so I can access the private property inside the class.



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So this is correct.



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This implicitly means C out arrow x c out x.



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Okay so this implicitly means this only.



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Okay.



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So what is the point I want to make here is.



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Friend function do not have access to this point.



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Okay so I am writing some points here.



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Okay.



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So first of all friend function do not have access to this point that way because friend functions are



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not the part of the class.



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Okay.



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Friend function are not the part of the class.



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So you do not have access to this pointer okay.



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Now the second point is we can put the friend function under any excess modifier.



175

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Okay so we can put these friend functions under any excess modifier.



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There will be no change okay.



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No effect.



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So the point is the excess modifiers do not work for friend function.



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Okay so I am writing here.



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Access modify it



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does not look for a friend function Y because the excess modified defined the accessibility of the members



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of the class and friend functions are not part of the class since friend function not the part of the



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class.



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Then access modify it cannot be used for friend function.



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So what I want to say here is so here the friend functions are in that the public we can move it to



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protected and we can also move it to private okay.



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There will be no changes okay.



188

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Now what I want is so we have a bus class inside the bus class.



189

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Let's say we have many functions so print one function similarly we have print to function print three



190

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functions print for function and so on.



191

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Okay so inside the bus class.



192

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Suppose we have many functions okay.



193

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And all these functions want to access the secrets of the class.



194

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Okay.



195

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All these functions wants to access the private and the protected properties of the upper class.



196

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So there are two ways to do this.



197

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So the first raise what we will do we will make all these functions as friend a function of their track



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class.



199

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Okay so this is the first Ruby.



200

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The second way the shortcut is what we will do.



201

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We will make the bus class as a friend of class.



202

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Okay we will make bus class.



203

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We will declare bus class as a friend of class.



204

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So the syntax is very simple



205

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okay.



206

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So let's combine these two lines.



207

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So what I want to do I want to make I want to make I want to declare I want to declare bus as a friend



208

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after class.



209

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So the syntax is very simple friend class bus okay.



210

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So what will happen with the help of this line.



211

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So with the help of this line what I want to say here is now the class bus is a friend of class.



212

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Okay so all the functions all the all the member function of the bus class can access all the properties



213

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of the truck class okay.



214

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Every member function of the bus class is now a friend of the truck class.



215

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Okay so these type of classes these type of classes are called Friend classes.



216

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Okay so these type of classes are called Friend classes so we know what our friend classes.



217

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Okay.



218

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Now the fourth point is the friendship is one way so we have one with friendship.



219

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So what is the meaning of when we.



220

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Friendship.



221

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So what is the meaning of a new friendship.



222

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So class drug has declared bus as his friend.



223

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So bus can access all the properties of the track class.



224

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Okay but divisive outside is not true.



225

00:13:15,480 --> 00:13:22,080

Okay bus can access all the properties of the truck class because truck has declared bus as its friend



226

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but the vice MSA is not true.



227

00:13:24,450 --> 00:13:28,970

Truck cannot access the private and the predicted properties of the bus class.



228

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Okay because bus has not declared Brooke as its friend.



229

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Now okay because bus has not declared drug as a stranger yet.



230

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Okay so the friendship is one where friendship okay.



231

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So when we friendship and we know what is a friend plus excess money if I will not vote for a friend



232

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glasses and Frank glasses do not have access to this point.



233

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Okay.



234

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Friend functions do not have access to this point.



235

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Okay so I hope everything is cleared.



236

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Thank you.