CODEWITHSUNDEEP
c++classinheritance
MD. Khairul Basar
MD. Khairul Basar

Reputation: 5110

Does derived class allocate memory for member variable?

#include<cstdio>
#include<iostream>
using namespace std;
class A
{
public:
    int x;
};
class B: public A
{
};
int main()
{
    B b;
    b.x=5;
    cout<<b.x<<endl;

    return 0;
}

i have the above code.it's all okay.but i want to know when i inherit class B from class A does the member variable x declared in class B too just like A or the class B just get access to the member variable x of class A ?
are there two variables with the same name in two different classes or there are only one variable and the objects of the both classes have access to it ?
if there are two different variables with the same name in two different classes then why, when an object of derived class is declared the constructor of base class is called ?

Upvotes: 0

Views: 823

Answers (1)

sanjayk79
sanjayk79

Reputation: 562

When you create an object of the derived class, a base class sub-object is embedded in the memory layout of the derived class object. So, to your question, there's only on variable that will be a part of the derived object. Since, we are only taking about non-static members here, each derived object gets its base-class sub-object laid out in memory. When you create a base class object, its a different piece of memory representing different object and has nothing to do with derived object created earlier.

Hope it clarifies your doubt!

This is a great book to understand C++ object model:

http://www.amazon.com/Inside-Object-Model-Stanley-Lippman/dp/0201834545/ref=sr_1_1?ie=UTF8&qid=1412535828&sr=8-1&keywords=inside+c%2B%2B+object+model

Upvotes: 1

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