(libc.info.gz) Networks Database

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 16.13 Networks Database
 =======================
 
 Many systems come with a database that records a list of networks known
 to the system developer.  This is usually kept either in the file
 `/etc/networks' or in an equivalent from a name server.  This data base
 is useful for routing programs such as `route', but it is not useful
 for programs that simply communicate over the network.  We provide
 functions to access this database, which are declared in `netdb.h'.
 
  -- Data Type: struct netent
      This data type is used to represent information about entries in
      the networks database.  It has the following members:
 
     `char *n_name'
           This is the "official" name of the network.
 
     `char **n_aliases'
           These are alternative names for the network, represented as a
           vector of strings.  A null pointer terminates the array.
 
     `int n_addrtype'
           This is the type of the network number; this is always equal
           to `AF_INET' for Internet networks.
 
     `unsigned long int n_net'
           This is the network number.  Network numbers are returned in
           host byte order; see  Byte Order.
 
    Use the `getnetbyname' or `getnetbyaddr' functions to search the
 networks database for information about a specific network.  The
 information is returned in a statically-allocated structure; you must
 copy the information if you need to save it.
 
  -- Function: struct netent * getnetbyname (const char *NAME)
      The `getnetbyname' function returns information about the network
      named NAME.  It returns a null pointer if there is no such network.
 
  -- Function: struct netent * getnetbyaddr (unsigned long int NET, int
           TYPE)
      The `getnetbyaddr' function returns information about the network
      of type TYPE with number NET.  You should specify a value of
      `AF_INET' for the TYPE argument for Internet networks.
 
      `getnetbyaddr' returns a null pointer if there is no such network.
 
    You can also scan the networks database using `setnetent',
 `getnetent' and `endnetent'.  Be careful when using these functions
 because they are not reentrant.
 
  -- Function: void setnetent (int STAYOPEN)
      This function opens and rewinds the networks database.
 
      If the STAYOPEN argument is nonzero, this sets a flag so that
      subsequent calls to `getnetbyname' or `getnetbyaddr' 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 netent * getnetent (void)
      This function returns the next entry in the networks database.  It
      returns a null pointer if there are no more entries.
 
  -- Function: void endnetent (void)
      This function closes the networks database.
 

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