man3/if_nameindex.3

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  26 .TH IF_NAMEINDEX 3 2019-03-06 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 if_nameindex, if_freenameindex \- get network interface names and indexes
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <net/if.h>
  32 .PP
  33 .BI "struct if_nameindex *if_nameindex(void);
  34 .BI "void if_freenameindex(struct if_nameindex *" "ptr" );
  35 .fi
  36 .SH DESCRIPTION
  37 The
  38 .BR if_nameindex ()
  39 function returns an array of
  40 .I if_nameindex
  41 structures, each containing information
  42 about one of the network interfaces on the local system.
  43 The
  44 .I if_nameindex
  45 structure contains at least the following entries:
  46 .PP
  47 .in +4n
  48 .EX
  49 unsigned int if_index; /* Index of interface (1, 2, ...) */
  50 char        *if_name;  /* Null-terminated name ("eth0", etc.) */
  51 .EE
  52 .in
  53 .PP
  54 The
  55 .I if_index
  56 field contains the interface index.
  57 The
  58 .I if_name
  59 field points to the null-terminated interface name.
  60 The end of the array is indicated by entry with
  61 .I if_index
  62 set to zero and
  63 .I if_name
  64 set to NULL.
  65 .PP
  66 The data structure returned by
  67 .BR if_nameindex ()
  68 is dynamically allocated and should be freed using
  69 .BR if_freenameindex ()
  70 when no longer needed.
  71 .SH RETURN VALUE
  72 On success,
  73 .BR if_nameindex ()
  74 returns pointer to the array;
  75 on error, NULL is returned, and
  76 .I errno
  77 is set appropriately.
  78 .SH ERRORS
  79 .BR if_nameindex ()
  80 may fail and set
  81 .I errno
  82 if:
  83 .TP
  84 .B ENOBUFS
  85 Insufficient resources available.
  86 .PP
  87 .BR if_nameindex ()
  88 may also fail for any of the errors specified for
  89 .BR socket (2),
  90 .BR bind (2),
  91 .BR ioctl (2),
  92 .BR getsockname (2),
  93 .BR recvmsg (2),
  94 .BR sendto (2),
  95 or
  96 .BR malloc (3).
  97 .SH VERSIONS
  98 The
  99 .BR if_nameindex ()
 100 function first appeared in glibc 2.1, but before glibc 2.3.4,
 101 the implementation supported only interfaces with IPv4 addresses.
 102 Support of interfaces that don't have IPv4 addresses is available only
 103 on kernels that support netlink.
 104 .SH ATTRIBUTES
 105 For an explanation of the terms used in this section, see
 106 .BR attributes (7).
 107 .TS
 108 allbox;
 109 lb lb lb
 110 l l l.
 111 Interface       Attribute       Value
 112 T{
 113 .BR if_nameindex (),
 114 .br
 115 .BR if_freenameindex ()
 116 T}      Thread safety   MT-Safe
 117 .TE
 118 .sp 1
 119 .SH CONFORMING TO
 120 POSIX.1-2001, POSIX.1-2008, RFC\ 3493.
 121 .PP
 122 This function first appeared in BSDi.
 123 .SH EXAMPLES
 124 The program below demonstrates the use of the functions described
 125 on this page.
 126 An example of the output this program might produce is the following:
 127 .PP
 128 .in +4n
 129 .EX
 130 $ \fB./a.out\fI
 131 1: lo
 132 2: wlan0
 133 3: em1
 134 .EE
 135 .in
 136 .SS Program source
 137 .EX
 138 #include <net/if.h>
 139 #include <stdio.h>
 140 #include <stdlib.h>
 141 #include <unistd.h>
 142
 143 int
 144 main(int argc, char *argv[])
 145 {
 146     struct if_nameindex *if_ni, *i;
 147
 148     if_ni = if_nameindex();
 149     if (if_ni == NULL) {
 150         perror("if_nameindex");
 151         exit(EXIT_FAILURE);
 152     }
 153
 154     for (i = if_ni; ! (i\->if_index == 0 && i\->if_name == NULL); i++)
 155         printf("%u: %s\en", i\->if_index, i\->if_name);
 156
 157     if_freenameindex(if_ni);
 158
 159     exit(EXIT_SUCCESS);
 160 }
 161 .EE
 162 .SH SEE ALSO
 163 .BR getsockopt (2),
 164 .BR setsockopt (2),
 165 .BR getifaddrs (3),
 166 .BR if_indextoname (3),
 167 .BR if_nametoindex (3),
 168 .BR ifconfig (8)