/*----d.h---*/
class D {
private: int num;
public:
D(int x) { this->num=x; printf(“Hello, this is %d\n”, x); }
work() { printf(“This is %d working\n”, this->num);
};
/*---a.cpp---*/
#include "d.h"
int g1=0;
D d1(1);

/*---b.cpp--*/
#include "d.h"
extern D d1;
D d2(2);
main() {
   int l2=0;
   D * d3=new D(3);
   d1.work();
   d2.work();
   d3->work();
}