#include <stdio.h>
#include <string.h>

struct save_rec {
  void *p;                    /* where */
  void *v;                    /* saved value */
  size_t sz;                  /* size of value */
};

void restore (void *s_)
{
  struct save_rec *s = s_;
  memcpy (s->p, s->v, s->sz);
}

#define bind(var,val)                                                   \
  for (struct {                                                         \
        struct save_rec r;                                              \
        int k;                                                          \
        __typeof__(var) old;                                            \
       } rec##__LINE__                                                  \
       __attribute__ ((cleanup (restore)))                              \
       = { { &var, &rec##__LINE__.old, sizeof (var) }, 0, var };        \
       (rec##__LINE__.k < 1) ? ((var = (val)), 1) : 0;                  \
       rec##__LINE__.k++)

/* Demo */

int xyz = 0;

void bar (void);
void baz (void);

void foo (void)
{
  bind (xyz, 42)
    bar ();
}
void bar (void)
{
  printf ("bar: xyz = %d\n", xyz);
  bind (xyz, 99)
    baz ();
  printf ("back in bar: xyz = %d\n", xyz);
}

void baz (void)
{
  printf ("baz: xyz = %d\n", xyz);
}

int main (int argc, char **argv)
{
  foo ();
  printf ("main: xyz = %d\n", xyz);
  return 0;
}