[aclug-L] Nice code and negative memory addresses

[Lars von dem Ast <mrprenzl@xxxxxxxxxx>]

Here's some nice code (taken from a C text):

/* pmath.c */

#define STRSIZ 20

typedef struct {
  char name[STRSIZ];
  double diameter;
  int moons;
  double orbit_time, rotation_time;
} planet_t;

int main(void)
{
  planet_t pl[2] = {{"Earth", 12713.5, 1, 1.0, 24.0},
                    {"Jupiter", 142800.0, 4, 11.9, 9.925}};
  int nm[5] = {4, 8, 10, 16, 22};
  planet_t *p;
  int *np;

  p = pl + 1;
  np = nm + 1;

  printf("sizeof (planet_t) = %d          sizeof (int) = %d\n",
         sizeof (planet_t), sizeof (int));
  printf("pl = %d                nm = %d\n", pl, nm);
  printf(" p = %d (pl + %d)      ", p, (int)p - (int)pl);
  printf("np = %d (nm + %d)\n", np, (int)np - (int)nm);
  printf(" p - pl = %d\n", p - pl);

}

Okay, here are the results:

sizeof (planet_t) = 48          sizeof (int) = 4
pl = -1073743632                nm = -1073743664
 p = -1073743584 (pl + 48)      np = -1073743660 (nm + 4)
 p - pl = 1

The pl, p, nm, and np variables should have memory addresses in them, but why 
are they negative numbers?

Lb
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