Function args declared as consts became non constant with definition

Code

class A
{
 public:
    void f(const int i);
};
void A::f(int i)
{
    std::cout<<++i<<std::endl;
}
int main()
{
   A a;
   a.f(1);
}

Why compiler does not give an error in this case ? Why the definition overrides the constant argument ? Also, when the argument is of type reference (&)

Is there any compiler flag to enable warning on these mentioned cases ?