.\"	$FreeBSD: src/lib/libc/net/getifaddrs.3,v 1.1.2.4 2001/08/31 10:15:14 ru Exp $
.\"	$KAME: getifaddrs.3,v 1.4 2000/05/17 14:13:14 itojun Exp $
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.Dd October 12, 1995
.Dt GETIFADDRS 3
.Os
.Sh NAME
.Nm getifaddrs
.Nd get interface addresses
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fd #include <ifaddrs.h>
.Ft int
.Fn getifaddrs "struct ifaddrs **ifap"
.Ft void
.Fn freeifaddrs "struct ifaddrs *ifp"
.Sh DESCRIPTION
The
.Fn getifaddrs
function stores a reference to a linked list of the network interfaces
on the local machine in the memory referenced by
.Fa ifap .
The list consists of
.Nm ifaddrs
structures, as defined in the include file
.Aq Pa ifaddrs.h .
The
.Nm ifaddrs
structure contains at least the following entries:
.Bd -literal
    struct ifaddrs   *ifa_next;         /* Pointer to next struct */
    char             *ifa_name;         /* Interface name */
    u_int             ifa_flags;        /* Interface flags */
    struct sockaddr  *ifa_addr;         /* Interface address */
    struct sockaddr  *ifa_netmask;      /* Interface netmask */
    struct sockaddr  *ifa_dstaddr;      /* P2P interface destination */
    void             *ifa_data;		/* Address specific data */
.Ed
.Pp
The
.Li ifa_next
field contains a pointer to the next structure on the list.
This field is
.Dv NULL
in last structure on the list.
.Pp
The
.Li ifa_name
field contains the interface name.
.Pp
The
.Li ifa_flags
field contains the interface flags, as set by
.Xr ifconfig 8
utility.
.Pp
The
.Li ifa_addr
field references either the address of the interface or the link level
address of the interface, if one exists, otherwise it is NULL.
(The
.Li sa_family
field of the
.Li ifa_addr
field should be consulted to determine the format of the
.Li ifa_addr
address.)
.Pp
The
.Li ifa_netmask
field references the netmask associated with
.Li ifa_addr ,
if one is set, otherwise it is NULL.
.Pp
The
.Li ifa_dstaddr
field references the destination address on a P2P interface,
if one exists, otherwise it contains the broadcast address.
.Pp
Note that as a convenience,
.Li ifa_broadaddr
is defined by a compiler
.Li #define
directive to be the same as
.Li ifa_dstaddr .
.Pp
The
.Li ifa_data
field references address family specific data.  For
.Dv AF_LINK
addresses it contains a pointer to the
.Fa struct if_data
(as defined in include file
.Aq Pa net/if.h )
which contains various interface attributes and statistics.
For all other address families, it contains a pointer to the
.Fa struct ifa_data
(as defined in include file
.Aq Pa net/if.h )
which contains per-address interface statistics.
.Pp
The data returned by
.Fn getifaddrs
is dynamically allocated and should be freed using
.Fn freeifaddrs
when no longer needed.
.Sh RETURN VALUES
.Rv -std getifaddrs
.Sh ERRORS
The
.Fn getifaddrs
may fail and set
.Va errno
for any of the errors specified for the library routines
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr malloc 3
or
.Xr sysctl 3 .
.Sh BUGS
If both
.Aq Pa net/if.h
and
.Aq Pa ifaddrs.h
are being included,
.Aq Pa net/if.h
.Em must
be included before
.Aq Pa ifaddrs.h .
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr sysctl 3 ,
.Xr networking 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
implementation first appeared in BSDi
.Bsx .