How to convert custom class pointer to unsigned int

I need to type cast custom class pointer to unsigned int value. Here is what I tired.

Class A{
};

int main()
{
A* a = foo();
unsigned int handler = reinterpret_cast<unsigned int>(a);
return 0;
}

It gives the warning warning C4302: 'reinterpret_cast': truncation from 'A *' to 'unsigned int'

What it the proper way to overcome this in C++ way