existing functionality questions

[Michael Tegtmeyer]

Hello,

I am trying to find out what the existing method of determining whether 
or not something (function for example) can access a field of a structure. 
For example:

class A {
   public:
     int pub_var;

     void foo(/*implicit this* */) {...}

   private:
     int private_var;
};

void bar(A a) {...}

In this example, foo can obviously access private_var but bar cannot. When 
examining function arguments, what is the accepted practice for finding 
out what members the function may access in the structure.

Thanks in advance,
Mike Tegtmeyer