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NAME

       if_nameindex,  if_freenameindex  -  get  network  interface  names  and
       indexes

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 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 ifa_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 ifa_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 appropriately.

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  interfaces  with  IPv4
       addresses.   Support  of  interfaces  that don't have IPv4 addresses is
       available only on kernels that support netlink.

CONFORMING TO

       RFC 3493, POSIX.1-2001.

       This function first appeared in BSDi.

EXAMPLE

       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(int argc, char *argv[])
       {
           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
", 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)

COLOPHON

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



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