.\"	$OpenBSD: getifaddrs.3,v 1.12 2005/07/22 04:50:51 jaredy Exp $
.\"	BSDI	getifaddrs.3,v 2.5 2000/02/23 14:51:59 dab 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 *ifap"
.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_broadaddr;    /* Interface broadcast address */
    struct sockaddr  *ifa_dstaddr;      /* P2P interface destination */
    void             *ifa_data;		/* Address specific data */
.Ed
.Bl -tag -width ifa_broadaddr
.It Fa ifa_next
Contains a pointer to the next structure on the list.
This field is set to
.Dv NULL
in the last structure on the list.
.It Fa ifa_name
Contains the interface name.
.It Fa ifa_flags
Contains the interface flags, as set by
.Xr ifconfig 8 .
.It Fa ifa_addr
References either the address of the interface or the link level
address of the interface, if one exists, otherwise it is
.Dv NULL .
(The
.Fa sa_family
field of the
.Fa ifa_addr
field should be consulted to determine the format of the
.Fa ifa_addr
address.)
.It Fa ifa_netmask
References the netmask associated with
.Fa ifa_addr ,
if one is set, otherwise it is
.Dv NULL .
.It Fa ifa_broadaddr
This field, which should only be referenced for non-P2P interfaces,
references the broadcast address associated with
.Fa ifa_addr ,
if one exists, otherwise it is
.Dv NULL .
.It Fa ifa_dstaddr
References the destination address on a P2P interface,
if one exists, otherwise it is
.Dv NULL .
.It Fa ifa_data
References address family specific data.
For
.Dv AF_LINK
addresses it contains a pointer to the
.Li 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
.Li struct ifa_data
(as defined in include file
.Aq Pa net/if.h )
which contains per-address interface statistics.
.El
.Pp
The data returned by
.Fn getifaddrs
is dynamically allocated and should be freed using
.Fn freeifaddrs
when no longer needed.
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.Va errno
is set to indicate the error.
.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 SEE ALSO
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr sysctl 3 ,
.Xr networking 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Fn getifaddrs
function first appeared in BSDI BSD/OS.
The function has been available on
.Ox
since
.Ox 2.7 .
.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 .