#include <stdio.h>
typedef struct A A_t;
typedef struct B B_t;

struct A
{
   float x;
   B_t *ptrB;
};

struct B
{
   float x;
   A_t *ptrA;
};

A_t a;
B_t b;
a.ptrB = &b;
b.ptrA = &a;

int main(void)
{
   return 0;
}