getnetbyaddr(3)

NAME

   getnetent,  getnetbyname,  getnetbyaddr,  setnetent,  endnetent  -  get
   network entry

SYNOPSIS

   #include <netdb.h>

   struct netent *getnetent(void);

   struct netent *getnetbyname(const char *name);

   struct netent *getnetbyaddr(uint32_t net, int type);

   void setnetent(int stayopen);

   void endnetent(void);

DESCRIPTION

   The getnetent()  function  reads  the  next  entry  from  the  networks
   database  and  returns  a  netent  structure  containing the broken-out
   fields from the entry.  A connection  is  opened  to  the  database  if
   necessary.

   The  getnetbyname()  function  returns a netent structure for the entry
   from the database that matches the network name.

   The getnetbyaddr() function returns a netent structure  for  the  entry
   from  the  database  that  matches the network number net of type type.
   The net argument must be in host byte order.

   The setnetent() function opens a connection to the database,  and  sets
   the  next  entry  to the first entry.  If stayopen is nonzero, then the
   connection to the database will not be closed between calls to  one  of
   the getnet*() functions.

   The endnetent() function closes the connection to the database.

   The netent structure is defined in <netdb.h> as follows:

       struct netent {
           char      *n_name;     /* official network name */
           char     **n_aliases;  /* alias list */
           int        n_addrtype; /* net address type */
           uint32_t   n_net;      /* network number */
       }

   The members of the netent structure are:

   n_name The official name of the network.

   n_aliases
          A NULL-terminated list of alternative names for the network.

   n_addrtype
          The type of the network number; always AF_INET.

   n_net  The network number in host byte order.

RETURN VALUE

   The  getnetent(),  getnetbyname() and getnetbyaddr() functions return a
   pointer to a statically allocated netent structure, or a  null  pointer
   if an error occurs or the end of the file is reached.

FILES

   /etc/networks
          networks database file

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   ┌───────────────┬───────────────┬───────────────────────────┐
   │Interface      │ Attribute     │ Value                     │
   ├───────────────┼───────────────┼───────────────────────────┤
   │getnetent()    │ Thread safety │ MT-Unsafe race:netent     │
   │               │               │ race:netentbuf env locale │
   ├───────────────┼───────────────┼───────────────────────────┤
   │getnetbyname() │ Thread safety │ MT-Unsafe race:netbyname  │
   │               │               │ env locale                │
   ├───────────────┼───────────────┼───────────────────────────┤
   │getnetbyaddr() │ Thread safety │ MT-Unsafe race:netbyaddr  │
   │               │               │ locale                    │
   ├───────────────┼───────────────┼───────────────────────────┤
   │setnetent(),   │ Thread safety │ MT-Unsafe race:netent env │
   │endnetent()    │               │ locale                    │
   └───────────────┴───────────────┴───────────────────────────┘
   In the above table, netent in race:netent signifies that if any of  the
   functions setnetent(), getnetent(), or endnetent() are used in parallel
   in different threads of a program, then data races could occur.

CONFORMING TO

   POSIX.1-2001, POSIX.1-2008, 4.3BSD.

NOTES

   In glibc versions before 2.2, the net argument of getnetbyaddr() was of
   type long.

SEE ALSO

   getnetent_r(3), getprotoent(3), getservent(3)
   RFC 1101

COLOPHON

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

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