The following shall be declared as functions and may also be defined
as macros. Function prototypes shall be provided.
struct passwd *getpwnam(const char *);
struct passwd *getpwuid(uid_t);
int getpwnam_r(const char *, struct passwd *, char *,
size_t, struct passwd **);
int getpwuid_r(uid_t, struct passwd *, char *,
size_t, struct passwd **);
void endpwent(void);
struct passwd *getpwent(void);
void setpwent(void);