Multipath inheritance :There are 2 Ways to Avoid this Ambiguity:

 6. A special case of hybrid inheritance: Multipath inheritance: 

A derived class with two base classes and these two base classes have one common base class is called multipath inheritance. Ambiguity can arise in this type of inheritance. 
Example:

CPP

// C++ program demonstrating ambiguity in Multipath
// Inheritance
 
#include <iostream>
using namespace std;
 
class ClassA {
public:
    int a;
};
 
class ClassB : public ClassA {
public:
    int b;
};
 
class ClassC : public ClassA {
public:
    int c;
};
 
class ClassD : public ClassB, public ClassC {
public:
    int d;
};
 
int main()
{
    ClassD obj;
 
    // obj.a = 10;                  // Statement 1, Error
    // obj.a = 100;                 // Statement 2, Error
 
    obj.ClassB::a = 10; // Statement 3
    obj.ClassC::a = 100; // Statement 4
 
    obj.b = 20;
    obj.c = 30;
    obj.d = 40;
 
    cout << " a from ClassB  : " << obj.ClassB::a;
    cout << "\n a from ClassC  : " << obj.ClassC::a;
 
    cout << "\n b : " << obj.b;
    cout << "\n c : " << obj.c;
    cout << "\n d : " << obj.d << '\n';
}
Output
 a from ClassB  : 10
 a from ClassC  : 100
 b : 20
 c : 30
 d : 40

Output: 

a from ClassB : 10
a from ClassC : 100
b : 20
c : 30
d : 40

In the above example, both ClassB and ClassC inherit ClassA, they both have a single copy of ClassA. However Class-D inherits both ClassB and ClassC, therefore Class-D has two copies of ClassA, one from ClassB and another from ClassC. 
If we need to access the data member of ClassA through the object of Class-D, we must specify the path from which a will be accessed, whether it is from ClassB or ClassC, bcoz compiler can’t differentiate between two copies of ClassA in Class-D.

There are 2 Ways to Avoid this Ambiguity: 

1) Avoiding ambiguity using the scope resolution operator: Using the scope resolution operator we can manually specify the path from which data member a will be accessed, as shown in statements 3 and 4, in the above example. 

CPP

obj.ClassB::a = 10;       // Statement 3
obj.ClassC::a = 100;      // Statement 4

Note: Still, there are two copies of ClassA in Class-D.
2) Avoiding ambiguity using the virtual base class: 

CPP

#include<iostream>
 
class ClassA
{
  public:
    int a;
};
 
class ClassB : virtual public ClassA
{
  public:
    int b;
};
 
class ClassC : virtual public ClassA
{
  public:
    int c;
};
 
class ClassD : public ClassB, public ClassC
{
  public:
    int d;
};
 
int main()
{
    ClassD obj;
 
    obj.a = 10;       // Statement 3
    obj.a = 100;      // Statement 4
 
    obj.b = 20;
    obj.c = 30;
    obj.d = 40;
 
    cout << "\n a : " << obj.a;
    cout << "\n b : " << obj.b;
    cout << "\n c : " << obj.c;
    cout << "\n d : " << obj.d << '\n';
}

Output: 

a : 100
b : 20
c : 30
d : 40

According to the above example, Class-D has only one copy of ClassA, therefore, statement 4 will overwrite the value of a, given in statement 3.

Comments

Post a Comment

Popular posts from this blog

Write a C++ program using classes and object to simulate result preparation system for 20 students. The data available for each student include roll no, name and marks in three subject. The percentage marks and grade are to be calculated from the above information. The percentage marks are the average marks and the grade is calculated as follows: % Marks Grade <50 'F >50<60 ‘D’ >60<75 'C' >75<90 'B' >=90<100 ‘A’  Here is a C++ program that simulates a result preparation system for 20 students using classes and objects. The program calculates the percentage marks and assigns grades based on the given criteria: # include <iostream> # include <string> # include <vector> using namespace std; class Student { private : int rollNo; string name; float marks[ 3 ]; float percentage; char grade; void calculatePercentage () { float total = 0 ; for ( int i = 0 ; i < 3 ; ...
Read more

Reading name, post and salary of 10 different employees and displaying those records whose salary is greater than 10000 using user defined function c++

Reading name, post and salary of 10 different employees and displaying those records whose salary is greater than 10000 using user defined function c++ #include <iostream> #include <string> struct Employee {     std::string name;     std::string post;     double salary; }; // Function to display records with salary greater than 10000 void displayHighSalaryEmployees(Employee employees[], int size) {     std::cout << "Employees with salary greater than 10000:\n";     for (int i = 0; i < size; ++i) {         if (employees[i].salary > 10000) {             std::cout << "Name: " << employees[i].name << "\n";             std::cout << "Post: " << employees[i].post << "\n";             std::cout << "Salary: " << employees[i].salary << "\n\n";     ...
Read more