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GETIFADDRS
Section: Linux Programmer's Manual (3)
Updated: 2009-01-23
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NAME
getifaddrs, freeifaddrs - get interface addresses
SYNOPSIS
#include <sys/types.h>
#include <ifaddrs.h>
int getifaddrs(struct ifaddrs **ifap);
void freeifaddrs(struct ifaddrs *ifa);
DESCRIPTION
The
getifaddrs()
function creates a linked list of structures describing
the network interfaces of the local system,
and stores the address of the first item of the list in
*ifap.
The list consists of
ifaddrs
structures, defined as follows:
struct ifaddrs {
struct ifaddrs *ifa_next; /* Next item in list */
char *ifa_name; /* Name of interface */
unsigned int ifa_flags; /* Flags from SIOCGIFFLAGS */
struct sockaddr *ifa_addr; /* Address of interface */
struct sockaddr *ifa_netmask; /* Netmask of interface */
union {
struct sockaddr *ifu_broadaddr;
/* Broadcast address of interface */
struct sockaddr *ifu_dstaddr;
/* Point-to-point destination address */
} ifa_ifu;
#define ifa_broadaddr ifa_ifu.ifu_broadaddr
#define ifa_dstaddr ifa_ifu.ifu_dstaddr
void *ifa_data; /* Address-specific data */
};
The
ifa_next
field contains a pointer to the next structure on the list,
or NULL if this is the last item of the list.
The
ifa_name
points to the null-terminated interface name.
The
ifa_flags
field contains the interface flags, as returned by the
SIOCGIFFLAGS
ioctl(2)
operation (see
netdevice(7)
for a list of these flags).
The
ifa_addr
field points to a structure containing the interface address.
(The
sa_family
subfield should be consulted to determine the format of the
address structure.)
The
ifa_netmask
field points to a structure containing the netmask associated with
ifa_addr,
if applicable for the address family.
Depending on whether the bit
IFF_BROADCAST
or
IFF_POINTOPOINT
is set in
ifa_flags
(only one can be set at a time),
either
ifa_broadaddr
will contain the broadcast address associated with
ifa_addr
(if applicable for the address family) or
ifa_dstaddr
will contain the destination address of the point-to-point interface.
The
ifa_data
field points to a buffer containing address-family-specific data;
this field may be NULL if there is no such data for this interface.
The data returned by
getifaddrs()
is dynamically allocated and should be freed using
freeifaddrs()
when no longer needed.
RETURN VALUES
On success,
getifaddrs()
returns zero;
on error, -1 is returned, and
errno
is set appropriately.
ERRORS
getifaddrs()
may fail and set
errno
for any of the errors specified for
socket(2),
bind(2),
getsockname(2),
recvmsg(2),
sendto(2),
malloc(3),
or
realloc(3).
VERSIONS
The
getifaddrs()
function first appeared in glibc 2.3, but before glibc 2.3.3,
the implementation only supported IPv4 addresses;
IPv6 support was added in glibc 2.3.3.
Support of address families other than IPv4 is only available
on kernels that support netlink.
CONFORMING TO
Not in POSIX.1-2001.
This function first appeared in BSDi and is
present on the BSD systems, but with slightly different
semantics documented---returning one entry per interface,
not per address.
This means
ifa_addr
and other fields can actually be NULL if the interface has no address,
and no link-level address is returned if the interface has an IP address
assigned.
Also, the way of choosing either
ifa_broadaddr
or
ifa_dstaddr
differs on various systems.
NOTES
The addresses returned on Linux will usually be the IPv4 and IPv6 addresses
assigned to the interface, but also one
AF_PACKET
address per interface containing lower-level details about the interface
and its physical layer.
In this case, the
ifa_data
field may contain a pointer to a
struct net_device_stats,
defined in
<linux/netdevice.h>,
which contains various interface attributes and statistics.
EXAMPLE
The program below demonstrates the use of
getifaddrs(),
freeifaddrs(),
and
getnameinfo(3).
Here is what we see when running this program on one system:
$ ./a.out
lo address family: 17 (AF_PACKET)
eth0 address family: 17 (AF_PACKET)
lo address family: 2 (AF_INET)
address: <127.0.0.1>
eth0 address family: 2 (AF_INET)
address: <10.1.1.4>
lo address family: 10 (AF_INET6)
address: <::1>
eth0 address family: 10 (AF_INET6)
address: <fe80::2d0:59ff:feda:eb51%eth0>
Program source
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NI_MAXHOST];
if (getifaddrs(&ifaddr) == -1) {
perror("getifaddrs");
exit(EXIT_FAILURE);
}
/* Walk through linked list, maintaining head pointer so we
can free list later */
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
family = ifa->ifa_addr->sa_family;
/* Display interface name and family (including symbolic
form of the latter for the common families) */
printf("%s address family: %d%s\n",
ifa->ifa_name, family,
(family == AF_PACKET) ? " (AF_PACKET)" :
(family == AF_INET) ? " (AF_INET)" :
(family == AF_INET6) ? " (AF_INET6)" : "");
/* For an AF_INET* interface address, display the address */
if (family == AF_INET || family == AF_INET6) {
s = getnameinfo(ifa->ifa_addr,
(family == AF_INET) ? sizeof(struct sockaddr_in) :
sizeof(struct sockaddr_in6),
host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if (s != 0) {
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\taddress: <%s>\n", host);
}
}
freeifaddrs(ifaddr);
exit(EXIT_SUCCESS);
}
SEE ALSO
bind(2),
getsockname(2),
socket(2),
packet(7),
ifconfig(8)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- Program source
-
- SEE ALSO
-
- COLOPHON
-
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