pig.c

#include <stddef.h>
#include <stdio.h>

typedef struct mystruct {
  int x, y;
  double f;
  char * hello;
} mystruct;

void
recover_struct(double * f)
{
  struct  mystruct butter;

  butter = *(mystruct *)((void*)(f) - offsetof(mystruct, f)); 

  printf("%s\n", butter.hello);
  printf("%d\n", butter.x);
  printf("%f\n", butter.f);
}


int
main(void)
{
  mystruct s = {.x = 10, .f = -66.6, .hello = "john" };
  
  double * f = &s.f;

  recover_struct(f);

  return 0;
}