Struct passwd 和 struct spwd

《UNIX高级环境编程》中没有给出struct passwd和struct spwd。查阅资料，如下：

struct passwd  {      char * pw_name; /* Username, POSIX.1 */      char * pw_passwd; /* Password */      __uid_t pw_uid; /* User ID, POSIX.1 */      __gid_t pw_gid; /* Group ID, POSIX.1 */      char * pw_gecos; /* Real Name or Comment field */      char * pw_dir; /* Home directory, POSIX.1 */      char * pw_shell; /* Shell Program, POSIX.1 */  };  struct spwd {    char *sp_namp; /* Login name */    char *sp_pwdp; /* Encrypted password */    long int sp_lstchg; /* Date of last change */    long int sp_min; /* Minimum number of days between changes */    long int sp_max; /* Maximum number of days between changes */    long int sp_warn; /* Number of days to warn user to change the password */    long int sp_inact; /* Number of days the account may be inactive */    long int sp_expire; /* Number of days since 1970-01-01 until account expires */    unsigned long int sp_flag; /* Reserved */};