int getifaddrs(struct ifaddrs **ifap);
void freeifaddrs(struct ifaddrs *ifa);
DESCRIPTION
The getifaddrs() function creates a linked list of structures describ‐
ing 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 *ifanext; /* Next item in list */
char *ifaname; /* Name of interface */
unsigned int ifaflags; /* Flags from SIOCGIFFLAGS */
struct sockaddr *ifaaddr; /* Address of interface */
struct sockaddr *ifanetmask; /* Netmask of interface */
union {
struct sockaddr *ifubroadaddr;
/* Broadcast address of interface */
struct sockaddr *ifudstaddr;
/* Point-to-point destination address */
} ifaifu;
#define ifabroadaddr ifaifu.ifubroadaddr
#define ifadstaddr ifaifu.ifudstaddr
void *ifadata; /* Address-specific data */
};
The ifanext field contains a pointer to the next structure on the
list, or NULL if this is the last item of the list.
The ifaname points to the null-terminated interface name.
The ifaflags field contains the interface flags, as returned by the
SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list of these
flags).
The ifaaddr field points to a structure containing the interface
address. (The safamily subfield should be consulted to determine the
format of the address structure.) This field may contain a NULL
pointer.
The ifanetmask field points to a structure containing the netmask
associated with ifaaddr, if applicable for the address family. This
field may contain a NULL pointer.
Depending on whether the bit IFFBROADCAST or IFFPOINTOPOINT is set in
ifaflags (only one can be set at a time), either ifabroadaddr will
contain the broadcast address associated with ifaaddr (if applicable
for the address family) or ifadstaddr will contain the destination
address of the point-to-point interface.
The ifadata field points to a buffer containing address-family-spe‐
cific 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 VALUE
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 supported only IPv4 addresses; IPv6 support
was added in glibc 2.3.3. Support of address families other than IPv4
is available only 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 docu‐
mented—returning one entry per interface, not per address. This means
ifaaddr 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 ifabroadaddr or
ifadstaddr 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 AFPACKET address per
interface containing lower-level details about the interface and its
physical layer. In this case, the ifadata field may contain a pointer
to a struct rtnllinkstats, defined in (in Linux 2.4
and earlier, struct netdevicestats, defined in ),
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 (AFPACKET)
eth0 address family: 17 (AFPACKET)
lo address family: 2 (AFINET)
address: <127.0.0.1>
eth0 address family: 2 (AFINET)
address: <10.1.1.4>
lo address family: 10 (AFINET6)
address: <::1>
eth0 address family: 10 (AFINET6)
address:
Program source
#include
#include
#include
#include
#include
#include
#include
int
main(int argc, char *argv[])
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NIMAXHOST];
if (getifaddrs(&ifaddr) == -1) {
perror("getifaddrs");
exit(EXITFAILURE);
}
/* Walk through linked list, maintaining head pointer so we
can free list later */
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifanext) {
if (ifa->ifaaddr == NULL)
continue;
family = ifa->ifaaddr->safamily;
/* Display interface name and family (including symbolic
form of the latter for the common families) */
printf("%s address family: %d%s\n",
ifa->ifaname, family,
(family == AFPACKET) ? " (AFPACKET)" :
(family == AFINET) ? " (AFINET)" :
(family == AFINET6) ? " (AFINET6)" : "");
/* For an AFINET* interface address, display the address */
if (family == AFINET || family == AFINET6) {
s = getnameinfo(ifa->ifaaddr,
(family == AFINET) ? sizeof(struct sockaddrin) :
sizeof(struct sockaddrin6),
host, NIMAXHOST, NULL, 0, NINUMERICHOST);
if (s != 0) {
printf("getnameinfo() failed: %s\n", gaistrerror(s));
exit(EXITFAILURE);
}
printf("\taddress: <%s>\n", host);
}
}
freeifaddrs(ifaddr);
exit(EXITSUCCESS);
}
SEE ALSO
bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
COLOPHON
This page is part of release 3.53 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/.
GNU 2012-11-11 GETIFADDRS(3)