if_nameindex man page on FreeBSD

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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

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <net/if.h>

     unsigned int
     if_nametoindex(const char *ifname);

     char *
     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 corresponding index.  If the specified interface does not exist,
     it returns 0.

     The if_indextoname() function maps the interface index specified in
     ifindex to it corresponding 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 corre‐
     sponding 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

     The if_freenameindex() function frees the dynamic memory that was allo‐
     cated by if_nameindex().

     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 getifaddrs(3).

     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 retriev‐
     ing 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.

     getifaddrs(3), networking(4)

     The if_nametoindex(), if_indextoname(), if_nameindex(), and
     if_freenameindex() functions conform to RFC 2553.

     The implementation first appeared in BSDi BSD/OS.

BSD			       November 23, 2005			   BSD

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