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#include <stdio.h>
#include <utmp.h>
#include <pwd.h>
#define UTMP "/etc/utmp"
#define NAMELEN 8
main()
{
FILE *fp;
struct utmp u;
struct passwd *p;
char tmp[NAMELEN+1];
struct passwd *getpwnam();
if ((fp = fopen(UTMP, "r")) == NULL) {
perror(UTMP);
exit(1);
}
/*
* For each entry...
*/
while (fread(&u, sizeof(u), 1, fp) != NULL) {
/*
* Skip non-logged in ports.
*/
if (u.ut_name[0] == NULL)
continue;
/*
* Make sure name is null-terminated.
*/
strncpy(tmp, u.ut_name, NAMELEN);
/*
* Skip non-existent users (shouldn't
* be any).
*/
if ((p = getpwnam(tmp)) == NULL)
continue;
/*
* Print the line. ctime() converts the time
* to ASCII format, it is described in Chapter
* 7, Telling Time and Timing Things. We
* ignore the format of the gecos field and
* just print the first 30 characters; in real
* life we would stop at a comma or some such.
*/
printf("%-10.8s %-10.8s %-30.30s %s", u.ut_name,
u.ut_line, p->pw_gecos, ctime(&u.ut_time));
}
fclose(fp);
exit(0);
}
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