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(libc.info)Services Database

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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 Note: Byte Order.

    `char *s_proto'
          This is the name of the protocol to use with this service.
          Note: 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 (Note:
     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.