man3/if_nameindex.3

   1 .\" Copyright (c) 2012 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
   2 .\" and Copyright (c) 2012 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .TH IF_NAMEINDEX 3 2021-03-22 "Linux man-pages (unreleased)"
   7 .SH NAME
   8 if_nameindex, if_freenameindex \- get network interface names and indexes
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <net/if.h>
  15 .PP
  16 .BI "struct if_nameindex *if_nameindex(" void );
  17 .BI "void if_freenameindex(struct if_nameindex *" "ptr" );
  18 .fi
  19 .SH DESCRIPTION
  20 The
  21 .BR if_nameindex ()
  22 function returns an array of
  23 .I if_nameindex
  24 structures, each containing information
  25 about one of the network interfaces on the local system.
  26 The
  27 .I if_nameindex
  28 structure contains at least the following entries:
  29 .PP
  30 .in +4n
  31 .EX
  32 unsigned int if_index; /* Index of interface (1, 2, ...) */
  33 char        *if_name;  /* Null\-terminated name ("eth0", etc.) */
  34 .EE
  35 .in
  36 .PP
  37 The
  38 .I if_index
  39 field contains the interface index.
  40 The
  41 .I if_name
  42 field points to the null-terminated interface name.
  43 The end of the array is indicated by entry with
  44 .I if_index
  45 set to zero and
  46 .I if_name
  47 set to NULL.
  48 .PP
  49 The data structure returned by
  50 .BR if_nameindex ()
  51 is dynamically allocated and should be freed using
  52 .BR if_freenameindex ()
  53 when no longer needed.
  54 .SH RETURN VALUE
  55 On success,
  56 .BR if_nameindex ()
  57 returns pointer to the array;
  58 on error, NULL is returned, and
  59 .I errno
  60 is set to indicate the error.
  61 .SH ERRORS
  62 .BR if_nameindex ()
  63 may fail and set
  64 .I errno
  65 if:
  66 .TP
  67 .B ENOBUFS
  68 Insufficient resources available.
  69 .PP
  70 .BR if_nameindex ()
  71 may also fail for any of the errors specified for
  72 .BR socket (2),
  73 .BR bind (2),
  74 .BR ioctl (2),
  75 .BR getsockname (2),
  76 .BR recvmsg (2),
  77 .BR sendto (2),
  78 or
  79 .BR malloc (3).
  80 .SH VERSIONS
  81 The
  82 .BR if_nameindex ()
  83 function first appeared in glibc 2.1, but before glibc 2.3.4,
  84 the implementation supported only interfaces with IPv4 addresses.
  85 Support of interfaces that don't have IPv4 addresses is available only
  86 on kernels that support netlink.
  87 .SH ATTRIBUTES
  88 For an explanation of the terms used in this section, see
  89 .BR attributes (7).
  90 .ad l
  91 .nh
  92 .TS
  93 allbox;
  94 lbx lb lb
  95 l l l.
  96 Interface       Attribute       Value
  97 T{
  98 .BR if_nameindex (),
  99 .BR if_freenameindex ()
 100 T}      Thread safety   MT-Safe
 101 .TE
 102 .hy
 103 .ad
 104 .sp 1
 105 .SH STANDARDS
 106 POSIX.1-2001, POSIX.1-2008, RFC\ 3493.
 107 .PP
 108 This function first appeared in BSDi.
 109 .SH EXAMPLES
 110 The program below demonstrates the use of the functions described
 111 on this page.
 112 An example of the output this program might produce is the following:
 113 .PP
 114 .in +4n
 115 .EX
 116 $ \fB./a.out\fI
 117 1: lo
 118 2: wlan0
 119 3: em1
 120 .EE
 121 .in
 122 .SS Program source
 123 .EX
 124 #include <net/if.h>
 125 #include <stdio.h>
 126 #include <stdlib.h>
 127 #include <unistd.h>
 128
 129 int
 130 main(int argc, char *argv[])
 131 {
 132     struct if_nameindex *if_ni, *i;
 133
 134     if_ni = if_nameindex();
 135     if (if_ni == NULL) {
 136         perror("if_nameindex");
 137         exit(EXIT_FAILURE);
 138     }
 139
 140     for (i = if_ni; ! (i\->if_index == 0 && i\->if_name == NULL); i++)
 141         printf("%u: %s\en", i\->if_index, i\->if_name);
 142
 143     if_freenameindex(if_ni);
 144
 145     exit(EXIT_SUCCESS);
 146 }
 147 .EE
 148 .SH SEE ALSO
 149 .BR getsockopt (2),
 150 .BR setsockopt (2),
 151 .BR getifaddrs (3),
 152 .BR if_indextoname (3),
 153 .BR if_nametoindex (3),
 154 .BR ifconfig (8)