IF_NAMETOINDEX(3) BSD Library Functions Manual IF_NAMETOINDEX(3)
if_nametoindex, if_indextoname, if_nameindex, if_freenameindex -- provide mappings between
interface names and indexes
if_nametoindex(const char *ifname);
if_indextoname(unsigned int ifindex, char *ifname);
struct if_nameindex *
if_freenameindex(struct if_nameindex *ptr);
The if_nametoindex() function maps the interface name specified in ifname to its correspond-
ing index. If the specified interface does not exist, it returns 0.
The if_indextoname() function maps the interface index specified in ifindex to it corre-
sponding name, which is copied into the buffer pointed to by ifname, which must be of at
least IFNAMSIZ bytes. This pointer is also the return value of the function. If there is
no interface corresponding to the specified index, NULL is returned.
The if_nameindex() function returns an array of if_nameindex structures, one structure per
interface, as defined in the include file <net/if.h>. The if_nameindex structure contains
at least the following entries:
unsigned int if_index; /* 1, 2, ... */
char *if_name; /* null terminated name: "le0", ... */
The end of the array of structures is indicated by a structure with an if_index of 0 and an
if_name of NULL. A NULL pointer is returned upon an error.
The if_freenameindex() function frees the dynamic memory that was allocated by
Upon successful completion, if_nametoindex() returns the index number of the interface. If
the interface is not found, a value of 0 is returned and errno is set to ENXIO. A value of
0 is also returned if an error occurs while retrieving the list of interfaces via
Upon successful completion, if_indextoname() returns ifname. If the interface is not found,
a NULL pointer is returned and errno is set to ENXIO. A NULL pointer is also returned if an
error occurs while retrieving the list of interfaces via getifaddrs(3).
The if_nameindex() returns a NULL pointer if an error occurs while retrieving the list of
interfaces via getifaddrs(3), or if sufficient memory cannot be allocated.
The if_nametoindex(), if_indextoname(), if_nameindex(), and if_freenameindex() functions
conform to IEEE Std 1003.1-2001 (``POSIX.1''), X/Open Networking Services Issue 5.2
(``XNS5.2''), and RFC 3493.
The implementation first appeared in BSD/OS.
BSD March 11, 2005 BSD