Two Layer Pointers

main.c

/* main.c */
#include <stdio.h>
#include "redirect_ptr.h"

int main(void)
{
    const char *firstday = NULL;
    const char *secondday = NULL;
    get_a_day(&firstday);
    get_a_day(&secondday);
    printf("%s\t%s\n", firstday, secondday);
    return 0;
}

redirect_ptr.c

/* redirect_ptr.c */
#include "redirect_ptr.h"

static const char *msg[] = {"Sunday", "Monday",
                            "Tuesday", "Wednesday",
                            "Thursday", "Friday",
                            "Saturday"};

void get_a_day(const char **pp)
{
  static int i = 0;
  *pp = msg[i%7];
  i++;
}

redirect_ptr.h

#ifndef TWOLAYERPOINTERS_REDIRECT_PTR_H
#define TWOLAYERPOINTERS_REDIRECT_PTR_H
extern void get_a_day(const char **);
#endif //TWOLAYERPOINTERS_REDIRECT_PTR_H