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IF_NAMEINDEX(3) Linux Programmer's Manual IF_NAMEINDEX(3)
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 exam‐
ple 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\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), ifcon‐
fig(8)
COLOPHON
This page is part of release 3.74 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
GNU 2012-11-21 IF_NAMEINDEX(3)
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