✏ EDIT: ifaddrs.h

/* ifaddrs.h -- declarations for getting network interface addresses
   Copyright (C) 2002-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifndef _IFADDRS_H
#define _IFADDRS_H	1

#include <features.h>
#include <sys/socket.h>

__BEGIN_DECLS

/* The `getifaddrs' function generates a linked list of these structures.
   Each element of the list describes one network interface.  */
struct ifaddrs
{
  struct ifaddrs *ifa_next;	/* Pointer to the next structure.  */

char *ifa_name;		/* Name of this network interface.  */
  unsigned int ifa_flags;	/* Flags as from SIOCGIFFLAGS ioctl.  */

struct sockaddr *ifa_addr;	/* Network address of this interface.  */
  struct sockaddr *ifa_netmask; /* Netmask of this interface.  */
  union
  {
    /* At most one of the following two is valid.  If the IFF_BROADCAST
       bit is set in `ifa_flags', then `ifa_broadaddr' is valid.  If the
       IFF_POINTOPOINT bit is set, then `ifa_dstaddr' is valid.
       It is never the case that both these bits are set at once.  */
    struct sockaddr *ifu_broadaddr; /* Broadcast address of this interface. */
    struct sockaddr *ifu_dstaddr; /* Point-to-point destination address.  */
  } ifa_ifu;
  /* These very same macros are defined by <net/if.h> for `struct ifaddr'.
     So if they are defined already, the existing definitions will be fine.  */
# ifndef ifa_broadaddr
#  define ifa_broadaddr	ifa_ifu.ifu_broadaddr
# endif
# ifndef ifa_dstaddr
#  define ifa_dstaddr	ifa_ifu.ifu_dstaddr
# endif

void *ifa_data;		/* Address-specific data (may be unused).  */
};

/* Create a linked list of `struct ifaddrs' structures, one for each
   network interface on the host machine.  If successful, store the
   list in *IFAP and return 0.  On errors, return -1 and set `errno'.

The storage returned in *IFAP is allocated dynamically and can
   only be properly freed by passing it to `freeifaddrs'.  */
extern int getifaddrs (struct ifaddrs **__ifap) __THROW;

/* Reclaim the storage allocated by a previous `getifaddrs' call.  */
extern void freeifaddrs (struct ifaddrs *__ifa)  __THROW;

__END_DECLS

#endif /* ifaddrs.h */

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