grp
struct group * getgrgid (gid_t gid);
gid_t gid
struct group * getgrnam (char const *name);
char const *name
struct group * getgrent (void);
void
void endgrent (void);
void setgrent (void);
#define id_t
#define gid_t
struct group { char * gr_name; gid_t gr_gid; char ** gr_mem; };