Programming Forums > Application Development > C++

sharadpro · Feb 4th, 2007, 12:23 PM

#include<iostream>
using namespace std;

class X
{
int x;
public:
int y;
protected:
int z;
};

class Y : public X
{
int a;
public:
int b;
protected:
int c;
};

int main()
{
cout<<sizeof(Y);
return 0;
}

According the output (24 on my machine) , even the variable x which was private in class X is being considered as a part of class Y?
Please explain!

lectricpharaoh · Feb 4th, 2007, 12:33 PM

What's to explain? Those private members will still be there, even if they ae not directly accessible. However, this doesn't mean they are not accessible at all; try putting a pair of get/set methods in the base class, and then call them.

The point is that private data members are (generally) intended to help the class keep track of its own internal state. Deriving a new class from this class doesn't mean it no longer has this responsibility, thus, it should have all the original members.

DaWei · Feb 4th, 2007, 1:14 PM

That's why it's called 'inheritance'

. Those other thangys are access modifiers.

pegasus001 · Feb 4th, 2007, 2:43 PM

Quote:

Originally Posted by sharadpro

even the variable x which was private in class X is being considered as a part of class Y?

They are family, it counts.

Feb 4th, 2007, 12:23 PM	#1
sharadpro Newbie Join Date: Feb 2006 Location: India Posts: 25 Rep Power: 0	Size of inherited class! (Toggle Plain Text) #include<iostream> using namespace std; class X { int x; public: int y; protected: int z; }; class Y : public X { int a; public: int b; protected: int c; }; int main() { cout<<sizeof(Y); return 0; } #include<iostream> using namespace std; class X { int x; public: int y; protected: int z; }; class Y : public X { int a; public: int b; protected: int c; }; int main() { cout<<sizeof(Y); return 0; } According the output (24 on my machine) , even the variable x which was private in class X is being considered as a part of class Y? Please explain!

Feb 4th, 2007, 12:33 PM	#2
lectricpharaoh SEXY SHOELESS GOD OF WAR! Join Date: Jun 2005 Location: Wet west coast of Canada Posts: 1,193 Rep Power: 5	What's to explain? Those private members will still be there, even if they ae not directly accessible. However, this doesn't mean they are not accessible at all; try putting a pair of get/set methods in the base class, and then call them. The point is that private data members are (generally) intended to help the class keep track of its own internal state. Deriving a new class from this class doesn't mean it no longer has this responsibility, thus, it should have all the original members. __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

Feb 4th, 2007, 1:14 PM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	That's why it's called 'inheritance' . Those other thangys are access modifiers. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Programming Forums > Application Development > C++

Size of inherited class!