Classes and member variables and fucntions

[danbaarts]

I am new to C++.

Can you access the value of a private member variable of one class from a member function of another class?

If so how? If not what are some other ways to get the value of a private member variable so it can be accessed outside of its class?

Thanks

Danny

 

[sskumar]

Hi Danny,
We can access a private member of a claa from other class member function i fthey are declared friend functions.

To simply get the private member outside a class,write a public member function that returns the value of the private member.

S.Senthil kumar

 

[BoulderBum]

You can only access private members of Class1 if Class2 is a "friend" of Class1 (which kind of ruins encapsulation) or if the Class2 "inherits" from Class1.

You can find out about inheritance and friend classes in C++ with a google search, but I think you want something simpler.

If you set Class1 up with a function returnPrivateMember(), then Class2 can call that function to get the variable.

E.g.

Class Class1
{
public:
Class1( int input ) { privateInt = input; }
int returnPrivateInt() { return privateInt; } //access to copy of private member
private:
int privateInt; //private member
};

class Class2
{
public:
Class2(): myClass1( 6 ) //initializes private Class1 with a value of 6
{ privateDouble = myClass1.returnPrivateInt(); } //assigns privateDouble with value returned by Class1 function
double returnPrivateDouble() { return privateDouble; }
private:
Class1 myClass1;
double privateDouble;
};

With such return-a-private-member functions, you can make sure the data of the class is still protected, while allowing other code to "see" the variable.

 

[BoulderBum]

Darn it, someone beat me to the punch!

 

[BoulderBum]

PS

Here's a clearer Class2

class Class2
{
public:
Class2(): myClass1( 6 ) //initializes private Class1 with a value of 6
{ privateDouble = myClass1.returnPrivateInt(); } //assigns privateDouble
//with value returned
//by Class1 function
double returnPrivateDouble() { return privateDouble; }
private:
Class1 myClass1; //initialized in constructor above
double privateDouble;
};

 

[BoulderBum]

PSS I lied about inheritance giving access to private members... I had a brain fart, it gives you access to protected members...

Ummmm, I'll just shut-up now.

 

[danbaarts]

thanks so much to both of you!

your help is greatly appreciated


danny (future answer giver)

 

[Zyrenthian]

You didn't lie Otherwise this quote would have never been said

"Remember, in C++, only friends can touch your private parts"



Matt