C++ Problem: Define that macro

I'm planning to post some C++ programming problems that I come across and shall post their solutions too (I'll try to post multiple solutions). Here goes the first one:

Problem:

DO_REPORTING is MACRO which when called at the start of a function with appropriate parameter, prints the value of the parameter at the start of the function and also somehow prints the value before leaving the function. For the following code expected output would be:

Before:2
After:4
Before:4
After:2

How would you get this output without changing anything in class A and inside main function?

  1 #include <iostream>
  2 using namespace std;
  3 
  4 #define DO_REPORTING(type,variable) ;
  5 
  6 class A{
  7 protected:
  8       int val;
  9 public:
 10       A(int v){
 11             val = v;
 12       }
 13       void FuncMult(){
 14             DO_REPORTING(int, val);
 15             val *= 2;
 16       }
 17       void FuncDiv(){
 18             DO_REPORTING(int, val);
 19             val /= 2;
 20       }
 21       int GetVal(){
 22             return val;
 23       }
 24 };
 25 
 26 int main(){
 27       A a(2);
 28       a.FuncMult();
 29       a.FuncDiv();
 30       return 0;
 31 }
 32 
 33 

Solution 1:

  1 #define DO_REPORTING(type,variable) Report<type> r(val);
  2 
  3 template <class T>
  4 class Report{
  5       T &val;
  6 public:
  7       Report(T &v):val(v){
  8             cout << "Before:" << val << endl;
  9       }
 10       ~Report(){
 11             cout << "After:" << val << endl;
 12       }
 13 };
 14