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The C and C++ Include Header Files

cat -n /usr/include/ifaddrs.h

     1	/* ifaddrs.h -- declarations for getting network interface addresses
     2	   Copyright (C) 2002-2026 Free Software Foundation, Inc.
     3	   This file is part of the GNU C Library.
     4	
     5	   The GNU C Library is free software; you can redistribute it and/or
     6	   modify it under the terms of the GNU Lesser General Public
     7	   License as published by the Free Software Foundation; either
     8	   version 2.1 of the License, or (at your option) any later version.
     9	
    10	   The GNU C Library is distributed in the hope that it will be useful,
    11	   but WITHOUT ANY WARRANTY; without even the implied warranty of
    12	   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    13	   Lesser General Public License for more details.
    14	
    15	   You should have received a copy of the GNU Lesser General Public
    16	   License along with the GNU C Library; if not, see
    17	   <https://www.gnu.org/licenses/>.  */
    18	
    19	#ifndef _IFADDRS_H
    20	#define _IFADDRS_H	1
    21	
    22	#include <features.h>
    23	#include <sys/socket.h>
    24	
    25	__BEGIN_DECLS
    26	
    27	/* The `getifaddrs' function generates a linked list of these structures.
    28	   Each element of the list describes one network interface.  */
    29	struct ifaddrs
    30	{
    31	  struct ifaddrs *ifa_next;	/* Pointer to the next structure.  */
    32	
    33	  char *ifa_name;		/* Name of this network interface.  */
    34	  unsigned int ifa_flags;	/* Flags as from SIOCGIFFLAGS ioctl.  */
    35	
    36	  struct sockaddr *ifa_addr;	/* Network address of this interface.  */
    37	  struct sockaddr *ifa_netmask; /* Netmask of this interface.  */
    38	  union
    39	  {
    40	    /* At most one of the following two is valid.  If the IFF_BROADCAST
    41	       bit is set in `ifa_flags', then `ifa_broadaddr' is valid.  If the
    42	       IFF_POINTOPOINT bit is set, then `ifa_dstaddr' is valid.
    43	       It is never the case that both these bits are set at once.  */
    44	    struct sockaddr *ifu_broadaddr; /* Broadcast address of this interface. */
    45	    struct sockaddr *ifu_dstaddr; /* Point-to-point destination address.  */
    46	  } ifa_ifu;
    47	  /* These very same macros are defined by <net/if.h> for `struct ifaddr'.
    48	     So if they are defined already, the existing definitions will be fine.  */
    49	# ifndef ifa_broadaddr
    50	#  define ifa_broadaddr	ifa_ifu.ifu_broadaddr
    51	# endif
    52	# ifndef ifa_dstaddr
    53	#  define ifa_dstaddr	ifa_ifu.ifu_dstaddr
    54	# endif
    55	
    56	  void *ifa_data;		/* Address-specific data (may be unused).  */
    57	};
    58	
    59	
    60	/* Create a linked list of `struct ifaddrs' structures, one for each
    61	   network interface on the host machine.  If successful, store the
    62	   list in *IFAP and return 0.  On errors, return -1 and set `errno'.
    63	
    64	   The storage returned in *IFAP is allocated dynamically and can
    65	   only be properly freed by passing it to `freeifaddrs'.  */
    66	extern int getifaddrs (struct ifaddrs **__ifap) __THROW;
    67	
    68	/* Reclaim the storage allocated by a previous `getifaddrs' call.  */
    69	extern void freeifaddrs (struct ifaddrs *__ifa)  __THROW;
    70	
    71	__END_DECLS
    72	
    73	#endif /* ifaddrs.h */