Calling volatile member function with not volatile object inC++

What happens, If calling volatile member function with not volatile object?

#include <iostream>
using namespace std;

class A 
{
private:
    int x;
public:
    void func(int a) volatile
    {
        x = a;
        cout<<x<<endl;
    }
};

int main() 
{
    A a1; // non volatile object
    a1.func(10);
    return 0;
}