C++: Pointer to members

Pointer to member operators are not an everyday operators that we use but those can be useful if used in the correct way. Pointer to member operator ::* is used to declare a pointer that points to a member variable, pointer or function of a class. The operators .* and ->* are used to access it.

Following is an example of how we can use Pointer to member function (also called member function pointer).

  1 #include <iostream>
  2 using namespace std;
  3 
  4 class A{
  5 public:
  6       A(){
  7       }
  8       int Func(int a){
  9               return a * 2;
 10       }
 11 
 12 };
 13 
 14 int main(){
 15       int (A::*fp)(int) = &A::Func;
 16 
 17       A a;
 18       cout << (a.*fp)(10) << endl;
 19 
 20       return 0;
 21 }
 22

Following is another (almost random) example of how we can write generic classes to wrap pointer to member function to use with multiple classes.

  1 #include <iostream>
  2 using namespace std;
  3 
  4 class A{
  5 public:
  6       int Func1(int a){
  7               return a * 2;
  8       }
  9 
 10 };
 11 
 12 class B{
 13 public:
 14       int Func2(int a){
 15               return a / 2;
 16       }
 17 
 18 };
 19 
 20 template <class T>
 21 class MemFnPtr
 22 {
 23 public:
 24       MemFnPtr(int (T::*fp)(int), T &t) : m_fp(fp), m_t(t){
 25       }
 26       int Fn(int n)
 27       {
 28             return ((m_t).*(m_fp))(n);
 29       }
 30  
 31       //member vars
 32       int (T::*m_fp)(int);
 33       T &m_t;
 34 };
 35 
 36 int main(){
 37       A a_obj;
 38  
 39       MemFnPtr<A> fp_a(&A::Func1, a_obj);
 40       cout << fp_a.Fn(10) << endl;
 41 
 42       B b_obj;
 43 
 44       MemFnPtr<B> fp_b(&B::Func2, b_obj);
 45       cout << fp_b.Fn(10) << endl;
 46 
 47       return 0;
 48 }
 49