typedef struct A A;typedef struct B B;typedef union U U;struct A{	int i;	float f;	double d;	char* s;	void* v;	char n[64];};union U{	int i;	float f;};struct B{	A a; B*	b;};extern int i;extern float f;extern double d;extern char* s;extern void* v;extern char n[64];extern A a;extern B* b;extern U u;extern int mi;extern float mf;extern double md;extern char* ms;extern void* mv;extern char mn[64];extern A ma;extern B* mb;