Bug in users command

[Dan Bernstein]

In article <18947 at rpp386.cactus.org> jfh at rpp386.cactus.org (John F Haugh II) writes:
> I think there is a bug in the code for "users" in the 4.3-reno
> source.  The problem is that the first user name is always printed
> as is the last user name.  If there is exactly one user on the
> system, and the user is logged on more than once, you get the
> user name twice.

Two other obvious bugs: first, the number of users is limited to 200;
second, scmp() appears to take the wrong argument types. Here is a
public-domain version that fixes these problems. This is derived from
the public-domain u.c published on comp.sources.unix as part of the pty
package; neither program was derived from Berkeley source.

---Dan

/* Public domain. */
#include <stdio.h>
#include <utmp.h>
#include <strings.h>
extern char *malloc();
#define PTYUTMP_FILE "/etc/utmp"

int compar(s,t)
char (**s)[8];
char (**t)[8];
{
 return -strncmp(&(**s)[0],&(**t)[0],8);
}

main()
{
 register FILE *fi;
 struct utmp ut;
 char (*us)[8];
 char (**up)[8];
 int lines = 0;
 int i = 0;
 
 if (!(fi = fopen(PTYUTMP_FILE,"r")))
  {
   fprintf(stderr,"users: cannot open %s\n",PTYUTMP_FILE);
   exit(1);
  }
 while (fread((char *) &ut,sizeof(ut),1,fi))
   if (ut.ut_name[0])
     lines++;
 (void) fclose(fi);
 us = malloc(sizeof(*us) * (lines + 50));
 up = malloc(sizeof(*up) * (lines + 50));
 if ((!us) || (!up))
  {
   fprintf(stderr,"users: cannot allocate space for user list\n");
   exit(2);
  }
 if (!(fi = fopen(PTYUTMP_FILE,"r")))
  {
   fprintf(stderr,"users: cannot open %s\n",PTYUTMP_FILE);
   exit(1);
  }
 while (fread((char *) &ut,sizeof(ut),1,fi))
   if ((ut.ut_name[0]) && (i < lines + 50))
    {
     (void) strncpy(us[i],ut.ut_name,8);
     up[i] = us + i;
     i++;
    }
 (void) fclose(fi);
 (void) qsort(up,i,sizeof(*up),compar);

 while (i-- > 0)
   (void) printf((i ? "%.8s " : "%.8s\n"),up[i]);

 (void) exit(0);
}