Friend functions are functions that are declared as friends of a class. This gives them special access to the private and protected members of that class. They are defined outside the class but have the same privileges as member functions.
Why use Friend Functions?
Algorithm Implementation: Sometimes, algorithms or operations can be implemented more efficiently outside a class, but they need access to the class's private members.
Non-Member Functions: You can define non-member functions that operate on objects of a class without making them member functions.
Overloading Operators: Friend functions are often used to overload operators for classes.
Example:
#include <iostream>
using namespace std;
class MyClass {
private:
int data;
public:
MyClass(int d) : data(d) {}
friend int add(MyClass obj1, MyClass obj2);
};
int add(MyClass obj1, MyClass obj2) {
return obj1.data + obj2.data;
}
int main() {
MyClass obj1(10), obj2(20);
int sum = add(obj1, obj2);
cout << "Sum: " << sum << endl;
return 0;
}
Output:
Sum: 30
Explanation:
In this example, the add() function is declared as a friend of the MyClass class. This allows it to access the private data member of the MyClass objects. The add() function takes two MyClass objects as arguments and returns their sum.
Important Points:
Friend functions are not members of the class.
Friend functions have access to the private and protected members of the class.
Friend functions can be defined outside the class.
Use friend functions judiciously, as they can break encapsulation.
When to Use Friend Functions
When you need to implement an algorithm that requires access to private members of a class.
When you want to overload operators for a class.
When you need to provide non-member functions that operate on objects of a class.
Alternatives to Friend Functions
Public Member Functions: If you only need to access the public members of a class, you can define public member functions instead of friend functions.
Inner Classes: You can create inner classes within a class to provide access to private members while maintaining encapsulation.
By understanding friend functions and their uses, you can write more efficient and flexible C++ code.
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