(libc.info.gz) Services Database

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 16.6.4 The Services Database
 ----------------------------
 
 The database that keeps track of "well-known" services is usually
 either the file `/etc/services' or an equivalent from a name server.
 You can use these utilities, declared in `netdb.h', to access the
 services database.  
 
  -- Data Type: struct servent
      This data type holds information about entries from the services
      database.  It has the following members:
 
     `char *s_name'
           This is the "official" name of the service.
 
     `char **s_aliases'
           These are alternate names for the service, represented as an
           array of strings.  A null pointer terminates the array.
 
     `int s_port'
           This is the port number for the service.  Port numbers are
           given in network byte order; see  Byte Order.
 
     `char *s_proto'
           This is the name of the protocol to use with this service.
            Protocols Database.
 
    To get information about a particular service, use the
 `getservbyname' or `getservbyport' functions.  The information is
 returned in a statically-allocated structure; you must copy the
 information if you need to save it across calls.
 
  -- Function: struct servent * getservbyname (const char *NAME, const
           char *PROTO)
      The `getservbyname' function returns information about the service
      named NAME using protocol PROTO.  If it can't find such a service,
      it returns a null pointer.
 
      This function is useful for servers as well as for clients; servers
      use it to determine which port they should listen on (
      Listening).
 
  -- Function: struct servent * getservbyport (int PORT, const char
           *PROTO)
      The `getservbyport' function returns information about the service
      at port PORT using protocol PROTO.  If it can't find such a
      service, it returns a null pointer.
 
 You can also scan the services database using `setservent',
 `getservent' and `endservent'.  Be careful when using these functions
 because they are not reentrant.
 
  -- Function: void setservent (int STAYOPEN)
      This function opens the services database to begin scanning it.
 
      If the STAYOPEN argument is nonzero, this sets a flag so that
      subsequent calls to `getservbyname' or `getservbyport' will not
      close the database (as they usually would).  This makes for more
      efficiency if you call those functions several times, by avoiding
      reopening the database for each call.
 
  -- Function: struct servent * getservent (void)
      This function returns the next entry in the services database.  If
      there are no more entries, it returns a null pointer.
 
  -- Function: void endservent (void)
      This function closes the services database.
 

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