man3/if_nametoindex.3

   1 .\" Copyright (c) 2012 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH IF_NAMETOINDEX 3 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   6 .SH NAME
   7 if_nametoindex, if_indextoname \- mappings between network interface
   8 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 "unsigned int if_nametoindex(const char *" "ifname" );
  17 .BI "char *if_indextoname(unsigned int ifindex, char *" ifname );
  18 .fi
  19 .SH DESCRIPTION
  20 The
  21 .BR if_nametoindex ()
  22 function returns the index of the network interface
  23 corresponding to the name
  24 .IR ifname .
  25 .PP
  26 The
  27 .BR if_indextoname ()
  28 function returns the name of the network interface
  29 corresponding to the interface index
  30 .IR ifindex .
  31 The name is placed in the buffer pointed to by
  32 .IR ifname .
  33 The buffer must allow for the storage of at least
  34 .B IF_NAMESIZE
  35 bytes.
  36 .SH RETURN VALUE
  37 On success,
  38 .BR if_nametoindex ()
  39 returns the index number of the network interface;
  40 on error, 0 is returned and
  41 .I errno
  42 is set to indicate the error.
  43 .PP
  44 On success,
  45 .BR if_indextoname ()
  46 returns
  47 .IR ifname ;
  48 on error, NULL is returned and
  49 .I errno
  50 is set to indicate the error.
  51 .SH ERRORS
  52 .BR if_nametoindex ()
  53 may fail and set
  54 .I errno
  55 if:
  56 .TP
  57 .B ENODEV
  58 No interface found with given name.
  59 .PP
  60 .BR if_indextoname ()
  61 may fail and set
  62 .I errno
  63 if:
  64 .TP
  65 .B ENXIO
  66 No interface found for the index.
  67 .PP
  68 .BR if_nametoindex ()
  69 and
  70 .BR if_indextoname ()
  71 may also fail for any of the errors specified for
  72 .BR socket (2)
  73 or
  74 .BR ioctl (2).
  75 .SH ATTRIBUTES
  76 For an explanation of the terms used in this section, see
  77 .BR attributes (7).
  78 .ad l
  79 .nh
  80 .TS
  81 allbox;
  82 lbx lb lb
  83 l l l.
  84 Interface       Attribute       Value
  85 T{
  86 .BR if_nametoindex (),
  87 .BR if_indextoname ()
  88 T}      Thread safety   MT-Safe
  89 .TE
  90 .hy
  91 .ad
  92 .sp 1
  93 .SH STANDARDS
  94 POSIX.1-2001, POSIX.1-2008, RFC\ 3493.
  95 .PP
  96 This function first appeared in BSDi.
  97 .SH SEE ALSO
  98 .BR getifaddrs (3),
  99 .BR if_nameindex (3),
 100 .BR ifconfig (8)