if_nameindex(3) - Man pages

if_nameindex(3)            Library Functions Manual            if_nameindex(3)

NAME
       if_nameindex,  if_freenameindex  -  get network interface names and in-
       dexes

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <net/if.h>

       struct if_nameindex *if_nameindex(void);
       void if_freenameindex(struct if_nameindex *ptr);

DESCRIPTION
       The if_nameindex() function returns an  array  of  if_nameindex  struc-
       tures,  each containing information about one of the network interfaces
       on the local system.  The if_nameindex structure contains at least  the
       following entries:

           unsigned int if_index; /* Index of interface (1, 2, ...) */
           char        *if_name;  /* Null-terminated name ("eth0", etc.) */

       The  if_index  field  contains  the interface index.  The if_name field
       points to the null-terminated interface name.  The end of the array  is
       indicated by entry with if_index set to zero and if_name set to NULL.

       The  data structure returned by if_nameindex() is dynamically allocated
       and should be freed using if_freenameindex() when no longer needed.

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

ERRORS
       if_nameindex() may fail and set errno if:

       ENOBUFS
              Insufficient resources available.

       if_nameindex() may also fail  for  any  of  the  errors  specified  for
       socket(2), bind(2), ioctl(2), getsockname(2), recvmsg(2), sendto(2), or
       malloc(3).

ATTRIBUTES
       For  an  explanation  of  the  terms  used in this section, see attrib-
       utes(7).
       ┌───────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                 │ Attribute     │ Value   │
       ├───────────────────────────────────────────┼───────────────┼─────────┤
       │ if_nameindex(), if_freenameindex()        │ Thread safety │ MT-Safe │
       └───────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS
       POSIX.1-2008, RFC 3493.

HISTORY
       glibc 2.1.  POSIX.1-2001.  BSDi.

       Before glibc 2.3.4, the implementation supported only  interfaces  with
       IPv4  addresses.   Support of interfaces that don't have IPv4 addresses
       is available only on kernels that support netlink.

EXAMPLES
       The program below demonstrates the use of the  functions  described  on
       this  page.  An example of the output this program might produce is the
       following:

           $ ./a.out
           1: lo
           2: wlan0
           3: em1

   Program source
       #include <net/if.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(void)
       {
           struct if_nameindex *if_ni, *i;

           if_ni = if_nameindex();
           if (if_ni == NULL) {
               perror("if_nameindex");
               exit(EXIT_FAILURE);
           }

           for (i = if_ni; !(i->if_index == 0 && i->if_name == NULL); i++)
               printf("%u: %s\n", i->if_index, i->if_name);

           if_freenameindex(if_ni);

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       getsockopt(2),   setsockopt(2),    getifaddrs(3),    if_indextoname(3),
       if_nametoindex(3), ifconfig(8)

Linux man-pages 6.7               2023-10-31                   if_nameindex(3)

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