CentOS 7.0 - man page for if_nametoindex (centos section 3)

IF_NAMETOINDEX(3)		    Linux Programmer's Manual			IF_NAMETOINDEX(3)

NAME
       if_nametoindex, if_indextoname - mappings between network interface names and indexes

SYNOPSIS
       #include <net/if.h>

       unsigned int if_nametoindex(const char *ifname);

       char *if_indextoname(unsigned int ifindex, char *ifname);

DESCRIPTION
       The  if_nametoindex() function returns the index of the network interface corresponding to
       the name ifname.

       The if_indextoname() function returns the name of the network interface	corresponding  to
       the  interface index ifindex.  The name is placed in the buffer pointed to by ifname.  The
       buffer must allow for the storage of at least IF_NAMESIZE bytes.

RETURN VALUE
       On success, if_nametoindex() returns the index number of the network interface; on  error,
       0 is returned and errno is set appropriately.

       On  success,  if_indextoname() returns ifname; on error, NULL is returned and errno is set
       appropriately.

ERRORS
       if_indextoname() may fail and set errno if:

       ENXIO  No interface found for the index.

       if_nametoindex() and if_indextoname() may also fail for any of the  errors  specified  for
       socket(2) or ioctl(2).

CONFORMING TO
       RFC 3493, POSIX.1-2001.

       This function first appeared in BSDi.

SEE ALSO
       getifaddrs(3), if_nameindex(3), ifconfig(8)

COLOPHON
       This  page  is  part of release 3.53 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/.

GNU					    2012-12-14				IF_NAMETOINDEX(3)