Calling const member function from non-const member function.

Most of the time we have to declare two version of same function i.e. one is const and other is non-const according to the needs to used that function on const data and non-const object. For example : lets have a simple example :


#include
#include
using namespace std;

class B {
public:
B(int j) : i(j) {}

void Show(void) const
{
cout<<"Const Version : i == ";
cout<<i;
}

void Show(void)
{
cout<<"Non-Const Version : i == ";
cout<<i;
}
private:
int i;
};

void main()
{
const B b(12);
cout<<"Caling from const object : \n";
b.Show();

B bb(10);
cout<<"\n\nCaling from non-const object : \n";
bb.Show();

_getch();
}

OUTPUT :
Caling from const object :

Const Version : i == 12

Caling from non-const object :
Non-Const Version : i == 10


In such a case we have to duplicate the code in both function. But duplication is always avoidable. So we have to find solution to this problem : There may be different solution exist but the most appropriate is given below : That is calling const function from non-const part :


void Show(void) const
{
cout<<"Const Version : i == ";
cout<<i;
}

void Show(void)
{
cout<<"Non-Const Version : i == ";
                // this->Show()               // Results into endless loop. Refer Note
(static_cast (this))->Show();
                //  or  (static_cast (*this)).Show();
}

It solve our purpose.
Note : If we directly call const Show function from non-const Show() means without casting it, results into a endless loop. Infact Show function recursively calls it self and formed endless loop. Thats why first cast this pointer to const and then call show function.

Thanx