Maps an interface name to its corresponding index.
    Format
      #include  <if.h>
      unsigned int if_nametoindex   ( const char *ifname );

1  –  Arguments

 ifname
    Points to a buffer that contains the interface name.

2  –  Description

    This function maps an interface name to its corresponding
    interface index number.

3  –  Return Values

    0 (zero)           Interface does not exist.
    x                  Upon successful conversion, the if_
                       nametoindex() function returns an interface
                       index number.