phunix/lib/libc/net/getifaddrs.3

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.Dd April 7, 2013
.Dt GETIFADDRS 3
.Os
.Sh NAME
.Nm getifaddrs
.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 *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
.In 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
.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
.Dv 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
.Dv NULL .
.Pp
The
.Li ifa_broadaddr
field,
which should only be referenced for non-P2P interfaces,
references the broadcast address associated with
.Li ifa_addr ,
if one exists, otherwise it is
.Dv NULL .
.Pp
The
.Li ifa_dstaddr
field references the destination address on a P2P interface,
if one exists, otherwise it is
.Dv NULL .
.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
.Pq as defined in include file Aq Pa net/if.h
which contains various interface attributes and statistics.
For all other address families, it is
.Dv NULL .
.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 EXAMPLES
The following example program prints a list of all addresses configured
on the system.
.Bd -literal -offset indent
#include \*[Lt]sys/types.h\*[Gt]
#include \*[Lt]sys/socket.h\*[Gt]
#include \*[Lt]stdio.h\*[Gt]
#include \*[Lt]ifaddrs.h\*[Gt]
#include \*[Lt]util.h\*[Gt]
#include \*[Lt]err.h\*[Gt]
#include \*[Lt]stdlib.h\*[Gt]

int
main(int argc, char *argv[])
{
	struct ifaddrs *ifa, *a;

	if (getifaddrs(\*[Am]ifa) == -1)
		err(EXIT_FAILURE, "getifaddrs");

	for (a = ifa; a; a = a->ifa_next) {
		char buf[1024];
		sockaddr_snprintf(buf, sizeof(buf), "%f %a",
		    a->ifa_addr);
		printf("%s %x %s\\n", a->ifa_name, a->ifa_flags, buf);
	}
	freeifaddrs(ifa);
	return EXIT_SUCCESS;
}
.Ed
.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
.Nm
implementation first appeared in
.Bsx .
.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 .