Friend function is a function, which can access the private and protected data member of a class. Using keyword friend, we can make function a friend function. Below is the prototype for friend function friend <return-type> function(<className>); Example: #include <iostream> using namespace std; class base { unsigned int m_int; public: base() { m_int = 20; } friend ostream& operator<<(ostream& s, const base& b); }; //Source File ostream& operator<<(ostream& s, const base& b) { s << b.m_int ; return s; } int main() { base b; cout << b << endl;…
Category: C++98
const member function
const member function does not allow to modify nonstatic data member value of an object. Below is the prototype for const function: <return-value> function() const;const function with empty definition look like: <return-value> <className>::function() const {}From the above you can see that with the const keyword, we can make function a const function. const function makes this pointer as pointer to a const because of this reason, we cannot modify object data i.e. nonstatic data member of an object. const function can be called from const object as well as non-const…
Mutable storage class specifier
mutable is the one of the storage specifier in C++. In general, const function does not allow to modify data members of an object who called it. However, with the help of mutable specifier, we can achieve it.Simple example shows use of mutable specifier. #include <iostream>using namespace std;class base { unsigned int m_int; mutable unsigned int m_mutableInt;public: base(unsigned int x, unsigned int y) { m_int = x; m_mutableInt = y; } void read() const { //const function m_int = 40; // Error: This is not allowed. m_mutableInt = 10; //…
Static function
Static function is used to access static data members of a class.Static function is called using class name and scope resolution operator. We do not need an object to call static function. //Header fileclass singleton { static singleton* m_instance; singleton() {} singleton& operator=(const singleton& ); singleton(const singleton& ); public: ~singleton() {} static singleton* getInstance(); }; //Source file singleton* singleton::m_instance = NULL;singleton* singleton::getInstance() { //static function accessing static data member m_instance if (NULL == m_instance) { return new singleton; …