if_nameindex, if_freenameindex - get network interface names and indexes

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

       The  if_nameindex()  function  returns  an  array of if_nameindex structures, 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.

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).

       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.out1:lo2:wlan03:em1Programsource
       #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);
       }

       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.

       Standard C library (libc, -lc)

       if_nameindex, if_freenameindex - get network interface names and indexes

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

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

Linux man-pages 6.9.1                              2024-06-15                                    if_nameindex(3)

       POSIX.1-2008, RFC 3493.

#include<net/if.h>structif_nameindex*if_nameindex(void);voidif_freenameindex(structif_nameindex*ptr);