class - How to access a member variable without instantiation, C++ -

suppose have class b gets value 'v' in constructor class a. how can read value class c? class c instantiated on demand, has created b , passed 'v' already. 'v' change in every instantiation. have tried make 'v' static in class b. work? not implement properly.

class {  public:  int* v;  b b1;  a(int* var) : v(var), b1(var) {}; } 

how access same version of 'v' c class? can define b , c in order achieve goal. cannot change purpose.

you cannot access 'v' has never passed class. instead can make static copy of member in class a. update every time instantiated this:

class {  public:    int* v;    static int* staticv;    ...// constructor etc } 

in .cc code of a:

int* a::staticv; ... a::staticv=this->v; 

now class can access value by:

a::staticv;