c++ - functions with const arguments Overloading ( Follow up)

Question

This is a follow up of the Previous Question

It got really complicated so I am starting a new thread to make my point clearer.( Didnt want to delete the previous thread because the other guys who gave valuable feedback dont not loose the reputation points they gained)

Updated Code: (Complies and Works)

#include <iostream>
 using std::cout;

 class Test {
         public:
         Test(){ }   
         int foo (const int) const;
         int foo (int );
 };  

 int main ()
 {   
         Test obj;
         int variable=0;  
         int output;
     do{ 
         output=obj.foo(3);        // Call the const function 
         cout<<"output::"<<output<<std::endl;
         output=obj.foo(variable); // Want to make it call the non const function 
         cout<<"output::"<<output<<std::endl;
         variable++; 
             usleep (2000000);
        }while(1);  
 }   

 int Test::foo(int a)
 {   
    cout<<"NON CONST"<<std::endl;
    a++;
    return a;
 }   

 int Test::foo (const int a) const
 {   
    cout<<"CONST"<<std::endl;
    return a;
 }   

Output (I get):

NON CONST
output::4
NON CONST
output::1
NON CONST
output::4
NON CONST
output::2
NON CONST
output::4
NON CONST
output::3
NON CONST
output::4
NON CONST
output::4
NON CONST
output::4
NON CONST
output::5

Output (I desired/had in mind)

CONST
output::3
NON CONST
output::1
CONST
output::3
NON CONST
output::2
CONST
output::3
NON CONST
output::3
CONST
output::3
NON CONST
output::4
CONST
output::3
NON CONST
output::5

Hope I have presented my question better. I know other ways to do it. but is this possible.

Answer 1

In C++, the function signatures

int Test::foo (const int a) const

and

int Test::foo (int a) const

are considered to be complete identical.

The reason that the const on the parameter is disregarded is because it can not affect the caller in any way. As the parameter is passed by value, a copy is made of the value provided by the caller. To the caller, it does not matter in any way if the called function can change that copy or not. For this reason, C++ ignores a top-level const-qualification on function parameters (top-level const can not occur if passing a reference), and goes even as far that int foo(int); is considered a correct prototype for the function

int foo(const int)
{
    /* ... */
}

In short, it is impossible in C++ to overload a function on the constness of (value) function parameters. To get the output you want, you could consider using a non-const reference parameter for your non-const overload.