使用getpwuid()和getgrgid()。

#include <pwd.h>
#include <grp.h>
#include <sys/stat.h>

struct stat info;
stat(filename, &info);  // Error check omitted
struct passwd *pw = getpwuid(info.st_uid);
struct group  *gr = getgrgid(info.st_gid);

// If pw != 0, pw->pw_name contains the user name
// If gr != 0, gr->gr_name contains the group name