Object with volatile private member

[Pararera]

Hi guys,
I'm writing code for Arduino, for interrupt function. Any variable must be volatile, so in case with no object it will look like this:

volatile int var;

void interrupt()
{
    var++;
}

But in next case I'm not sure should I create object with volatile tag, or modifier function, or just private variable?

class objclass {
public:
addValue(int value) { var += value; }

private:
int var;
};


objclass object;

void interrupt()
{
    object.addValue(1);
}

Where I should put volatile? Thanks!

[JLBorges]

struct A {

    volatile int i = 0 ;
    int j = 0 ;
};

volatile A a1 ; // all members of a1 are volatile:
                // both a1.i and a1.j are of type 'volatile int'

A a2 ; // a2.i is volatile, a2.j is not 

[Pararera]

Thanks for explonation