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.\"	BSDI	getifaddrs.3,v 2.5 2000/02/23 14:51:59 dab Exp
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.Dd $Mdocdate: January 12 2018 $
.Dt GETIFADDRS 3
.Os
.Sh NAME
.Nm getifaddrs ,
.Nm freeifaddrs
.Nd get interface addresses
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In 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
.Vt ifaddrs
structures, as defined in the include file
.In ifaddrs.h .
The
.Vt 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
This field, which should only be referenced for P2P interfaces,
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
.Vt struct if_data
(as defined in include file
.In net/if.h )
which contains various interface attributes and statistics.
For all other address families,
.Fa ifa_data
is
.Dv NULL .
.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
.Rv -std
.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 2 .
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr sysctl 2 ,
.Xr netintro 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Fn getifaddrs
function first appeared in BSDI
.Bsx .
The function has been available on
.Ox
since
.Ox 2.7 .
.Sh BUGS
If both
.In net/if.h
and
.In ifaddrs.h
are being included,
.In net/if.h
.Em must
be included before
.In ifaddrs.h .