if_nameindex(3)                                       Library Functions Manual                                      if_nameindex(3)

NAME
       if_nameindex, if_freenameindex - get network interface names and indexes

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 structures, each containing information about one of the net‐
       work 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).

VERSIONS
       The  if_nameindex()  function  first appeared in glibc 2.1, but before glibc 2.3.4, the implementation supported only inter‐
       faces with IPv4 addresses.  Support of interfaces that don't have IPv4 addresses is available only on kernels  that  support
       netlink.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌─────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                                                        │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │if_nameindex(), if_freenameindex()                                                               │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS
       POSIX.1-2001, POSIX.1-2008, RFC 3493.

       This function first appeared in BSDi.

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 6.03                                         2022-12-15                                             if_nameindex(3)