if_nameindex(3) — Linux manual page

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 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
       attributes(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)

COLOPHON

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       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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       man-pages@man7.org

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

Pages that refer to this page: if_nametoindex(3)

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