if_freenameindex(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(\nvoid\n);\n
\nvoid if_freenameindex(struct if_nameindex *\nptr\n);

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).

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:

$ \n./a.out\n
\n1: lo\n
\n2: wlan0\n
\n3: em1\n

Program source#

#include <net/if.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(void)
{
\n
    struct if_nameindex *if_ni, *i;
\n
    if_ni = if_nameindex();
\n
    if (if_ni == NULL) {
\n
        perror("if_nameindex");
\n
        exit(EXIT_FAILURE);
\n
    }
\n
    for (i = if_ni; !(i->if_index == 0 && i->if_name == NULL); i++)
\n
        printf("%u: %s\n", i->if_index, i->if_name);
\n
    if_freenameindex(if_ni);
\n
    exit(EXIT_SUCCESS);
}

SEE ALSO#

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