struct protoent 구조, getprotobyname 및 관련 함수

/* Description of data base entry for a single service.  */
struct protoent
{
  char *p_name;         /* Official protocol name.  */
  char **p_aliases;     /* Alias list.  */
  int p_proto;          /* Protocol number.  */
};

/* Open protocol data base files and mark them as staying open even
   after a later search if STAY_OPEN is non-zero.
   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern void setprotoent (int __stay_open);

/* Close protocol data base files and clear `stay open' flag.
   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern void endprotoent (void);

/* Get next entry from protocol data base file.  Open data base if
   necessary.
   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern struct protoent *getprotoent (void);

/* Return entry from protocol data base for network with NAME.
   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern struct protoent *getprotobyname (__const char *__name);

/* Return entry from protocol data base which number is PROTO.
   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern struct protoent *getprotobynumber (int __proto);