Template function taking class as parameter

I want to write something like that:

template <class T>
void write(my_out_stream &output_stream, T &data)
{

}

class A 
{
public:
    int a;
    int b;
};

class B 
{
public:
    int c;
}

int main() 
{
    A a;
    B b;
    my_out_stream mos;

    write(mos, a);
    write(mos, b);

    return 0;
}

Is it possible? If not, how I should create function write, if I don't know, which classes will be use its.

Note, that I can not change call way (write(mos, a)). I am able to to change only signature of write.