GETIFADDRS(3SOCKET) Sockets Library Functions GETIFADDRS(3SOCKET)

NAME

getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS

cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
#include <ifaddrs.h>


int getifaddrs(struct ifaddrs **ifap);


void freeifaddrs(struct ifaddrs *ifp);

DESCRIPTION

The getifaddrs() function is used to obtain the list of network
interfaces on the local machine. A reference to a linked list of
ifaddrs structures, as defined in <ifaddrs.h>, is stored in the
memory referenced by ifap. Each structure in the list describes one
network interface address, and is of the form:


struct ifaddrs {
struct ifaddrs *ifa_next;
char *ifa_name;
uint64_t ifa_flags;
struct sockaddr *ifa_addr;
struct sockaddr *ifa_netmask;
union {
struct sockaddr *ifu_broadaddr;
struct sockaddr *ifu_dstaddr;
} ifa_ifu;
void *ifa_data;
};
#define ifa_broadaddr ifa_ifu.ifu_broadaddr
#define ifa_dstaddr ifa_ifu.ifu_dstaddr


The list is traversed by following the ifa_next pointer. This member
is NULL on the last structure in the list.


The ifa_name member contains the interface name.


The ifa_flags member contains the interface flags.


The ifa_addr member references the address of the interface. Use the
sa_family member of this structure to determine the format of the
address, as described in socket.h(3HEAD).


The ifa_netmask member references the netmask associated with
ifa_addr, or NULL if one is not set.


If the IFF_BROADCAST bit is set in ifa_flags, then ifa_broadaddr is
valid, or NULL if not present. If the IFF_POINTOPOINT bit is set,
then ifa_dstaddr is valid, or NULL if not present. These two flags
are mutually exclusive; see if_tcp(4P) for more information.


The ifa_data member is specific to the address family. It is
currently only available for AF_LINK entries where it contains a
pointer to the struct if_data (as defined in if.h(3HEAD)).


The memory used by getifaddrs() to back the list is dynamically
allocated. It should be freed using freeifaddrs().

RETURN VALUES

If successful, getifaddrs() returns the value 0; otherwise it returns
-1 and sets errno to indicate the error.

ERRORS

The getifaddrs() function may fail and set errno for any of the
errors specified for the library routines ioctl(2), socket(3SOCKET),
and malloc(3C).

ATTRIBUTES

+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

ioctl(2), malloc(3C), socket.h(3HEAD), sockaddr(3SOCKET),
socket(3SOCKET), if_tcp(4P), attributes(7), ifconfig(8), ipadm(8)

NOTES

This function lists interfaces of type AF_INET, AF_INET6, and
AF_LINK. For AF_INET and AF_INET6 only interfaces with the IFF_UP
flag set are listed; see if_tcp(4P) and ifconfig(8) for more
information. For AF_LINK entries the interface index is only
available when the link is plumbed.

February 1, 2022 GETIFADDRS(3SOCKET)