if_nameindex(3)

1if_nameindex(3)            Library Functions Manual            if_nameindex(3)
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NAME

6       if_nameindex,  if_freenameindex  -  get network interface names and in‐
7       dexes
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LIBRARY

10       Standard C library (libc, -lc)
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SYNOPSIS

13       #include <net/if.h>
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15       struct if_nameindex *if_nameindex(void);
16       void if_freenameindex(struct if_nameindex *ptr);
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DESCRIPTION

19       The if_nameindex() function returns an  array  of  if_nameindex  struc‐
20       tures,  each containing information about one of the network interfaces
21       on the local system.  The if_nameindex structure contains at least  the
22       following entries:
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24           unsigned int if_index; /* Index of interface (1, 2, ...) */
25           char        *if_name;  /* Null-terminated name ("eth0", etc.) */
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27       The  if_index  field  contains  the interface index.  The if_name field
28       points to the null-terminated interface name.  The end of the array  is
29       indicated by entry with if_index set to zero and if_name set to NULL.
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31       The  data structure returned by if_nameindex() is dynamically allocated
32       and should be freed using if_freenameindex() when no longer needed.
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RETURN VALUE

35       On success, if_nameindex() returns pointer to the array; on error, NULL
36       is returned, and errno is set to indicate the error.
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ERRORS

39       if_nameindex() may fail and set errno if:
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41       ENOBUFS
42              Insufficient resources available.
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44       if_nameindex()  may  also  fail  for  any  of  the errors specified for
45       socket(2), bind(2), ioctl(2), getsockname(2), recvmsg(2), sendto(2), or
46       malloc(3).
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ATTRIBUTES

49       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
50       tributes(7).
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52       ┌────────────────────────────────────────────┬───────────────┬─────────┐
53       │Interface                                   │ Attribute     │ Value   │
54       ├────────────────────────────────────────────┼───────────────┼─────────┤
55       │if_nameindex(), if_freenameindex()          │ Thread safety │ MT-Safe │
56       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

59       POSIX.1-2008, RFC 3493.
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HISTORY

62       glibc 2.1.  POSIX.1-2001.  BSDi.
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64       Before glibc 2.3.4, the implementation supported only  interfaces  with
65       IPv4  addresses.   Support of interfaces that don't have IPv4 addresses
66       is available only on kernels that support netlink.
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EXAMPLES

69       The program below demonstrates the use of the  functions  described  on
70       this  page.  An example of the output this program might produce is the
71       following:
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73           $ ./a.out
74           1: lo
75           2: wlan0
76           3: em1
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78   Program source
79       #include <net/if.h>
80       #include <stdio.h>
81       #include <stdlib.h>
82       #include <unistd.h>
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84       int
85       main(void)
86       {
87           struct if_nameindex *if_ni, *i;
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89           if_ni = if_nameindex();
90           if (if_ni == NULL) {
91               perror("if_nameindex");
92               exit(EXIT_FAILURE);
93           }
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95           for (i = if_ni; !(i->if_index == 0 && i->if_name == NULL); i++)
96               printf("%u: %s\n", i->if_index, i->if_name);
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98           if_freenameindex(if_ni);
99
100           exit(EXIT_SUCCESS);
101       }
102