Q:

Write a program that describes the safe way to access one object to another in C++?

YasminRadwan26

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2022-06-26

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Write a program that describes the safe way to access one object to another in C++?

C++ programming, Interview questions, C++ programming Interview-questions,

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YasminRadwan26

2022-06-26

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Answer:

Let see an example, where class A object is calling from class B. In the first example, I am calling class a function in the constructor of class B.

#include<iostream>
using namespace std;
class A
{
public:
    A()
    {
        cout << "class  A constructor" <<endl;
    }
    void f()
    {
        cout << "class  A function" <<endl;
    }
};
class B
{
public:
    B(class A *a)
    {
        cout << "class  B constructor" <<endl;
        a->f();
    }
};
extern class A a;
class B b(&a);
class A a;
int main()
{
    return 0;
}

Output:

class B constructor

class A function

class A constructor

-------------------------------------------------------------------------------------------------------

You can see when we are running the code class A function is calling before the calling of the constructor of class A. It is unsafe and might show undefined behavior.

So below we are modifying the code for safety. In the below code function only call after the construction of class A.

#include<iostream>
using namespace std;
class A
{
public:
    A()
    {
        cout << "class  A constructor" <<endl;
    }
    void f()
    {
        cout << "class  A function" <<endl;
    }
};
class B
{
public:
    B(class A *a)
        : pFun(a)
    {
        cout << "class  B constructor" <<endl;
    }
    void init()
    {
        pFun->f();
    }
    class A *pFun;
};
extern class A a;
class B b(&a);
class A a;
int main()
{
    //Now Safe to access one object from another
    b.init();
    
    return 0;
}

Output:

class B constructor

class A constructor

class A function

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