1getifaddrs(3) Library Functions Manual getifaddrs(3)
2
6 getifaddrs, freeifaddrs - get interface addresses
7
9 Standard C library (libc, -lc)
10
12 #include <sys/types.h>
13 #include <ifaddrs.h>
14 int getifaddrs(struct ifaddrs **ifap);
16 void freeifaddrs(struct ifaddrs *ifa);
17
19 The getifaddrs() function creates a linked list of structures describ‐
20 ing the network interfaces of the local system, and stores the address
21 of the first item of the list in *ifap. The list consists of ifaddrs
22 structures, defined as follows:
23 struct ifaddrs {
25 struct ifaddrs *ifa_next; /* Next item in list */
26 char *ifa_name; /* Name of interface */
27 unsigned int ifa_flags; /* Flags from SIOCGIFFLAGS */
28 struct sockaddr *ifa_addr; /* Address of interface */
29 struct sockaddr *ifa_netmask; /* Netmask of interface */
30 union {
31 struct sockaddr *ifu_broadaddr;
32 /* Broadcast address of interface */
33 struct sockaddr *ifu_dstaddr;
34 /* Point-to-point destination address */
35 } ifa_ifu;
36 #define ifa_broadaddr ifa_ifu.ifu_broadaddr
37 #define ifa_dstaddr ifa_ifu.ifu_dstaddr
38 void *ifa_data; /* Address-specific data */
39 };
40 The ifa_next field contains a pointer to the next structure on the
42 list, or NULL if this is the last item of the list.
43 The ifa_name points to the null-terminated interface name.
45 The ifa_flags field contains the interface flags, as returned by the
47 SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list of these
48 flags).
49 The ifa_addr field points to a structure containing the interface ad‐
51 dress. (The sa_family subfield should be consulted to determine the
52 format of the address structure.) This field may contain a null
53 pointer.
54 The ifa_netmask field points to a structure containing the netmask as‐
56 sociated with ifa_addr, if applicable for the address family. This
57 field may contain a null pointer.
58 Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
60 ifa_flags (only one can be set at a time), either ifa_broadaddr will
61 contain the broadcast address associated with ifa_addr (if applicable
62 for the address family) or ifa_dstaddr will contain the destination ad‐
63 dress of the point-to-point interface.
64 The ifa_data field points to a buffer containing address-family-spe‐
66 cific data; this field may be NULL if there is no such data for this
67 interface.
68 The data returned by getifaddrs() is dynamically allocated and should
70 be freed using freeifaddrs() when no longer needed.
71
73 On success, getifaddrs() returns zero; on error, -1 is returned, and
74 errno is set to indicate the error.
75
77 getifaddrs() may fail and set errno for any of the errors specified for
78 socket(2), bind(2), getsockname(2), recvmsg(2), sendto(2), malloc(3),
79 or realloc(3).
80
82 For an explanation of the terms used in this section, see at‐
83 tributes(7).
84 ┌────────────────────────────────────────────┬───────────────┬─────────┐
86 │Interface │ Attribute │ Value │
87 ├────────────────────────────────────────────┼───────────────┼─────────┤
88 │getifaddrs(), freeifaddrs() │ Thread safety │ MT-Safe │
89 └────────────────────────────────────────────┴───────────────┴─────────┘
90
92 None.
93
95 This function first appeared in BSDi and is present on the BSD systems,
96 but with slightly different semantics documented—returning one entry
97 per interface, not per address. This means ifa_addr and other fields
98 can actually be NULL if the interface has no address, and no link-level
99 address is returned if the interface has an IP address assigned. Also,
100 the way of choosing either ifa_broadaddr or ifa_dstaddr differs on var‐
101 ious systems.
102 getifaddrs() first appeared in glibc 2.3, but before glibc 2.3.3, the
104 implementation supported only IPv4 addresses; IPv6 support was added in
105 glibc 2.3.3. Support of address families other than IPv4 is available
106 only on kernels that support netlink.
107
109 The addresses returned on Linux will usually be the IPv4 and IPv6 ad‐
110 dresses assigned to the interface, but also one AF_PACKET address per
111 interface containing lower-level details about the interface and its
112 physical layer. In this case, the ifa_data field may contain a pointer
113 to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
114 and earlier, struct net_device_stats, defined in <linux/netdevice.h>),
115 which contains various interface attributes and statistics.
116
118 The program below demonstrates the use of getifaddrs(), freeifaddrs(),
119 and getnameinfo(3). Here is what we see when running this program on
120 one system:
121 $ ./a.out
123 lo AF_PACKET (17)
124 tx_packets = 524; rx_packets = 524
125 tx_bytes = 38788; rx_bytes = 38788
126 wlp3s0 AF_PACKET (17)
127 tx_packets = 108391; rx_packets = 130245
128 tx_bytes = 30420659; rx_bytes = 94230014
129 em1 AF_PACKET (17)
130 tx_packets = 0; rx_packets = 0
131 tx_bytes = 0; rx_bytes = 0
132 lo AF_INET (2)
133 address: <127.0.0.1>
134 wlp3s0 AF_INET (2)
135 address: <192.168.235.137>
136 lo AF_INET6 (10)
137 address: <::1>
138 wlp3s0 AF_INET6 (10)
139 address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>
140 Program source
142 #define _GNU_SOURCE /* To get defns of NI_MAXSERV and NI_MAXHOST */
144 #include <arpa/inet.h>
145 #include <sys/socket.h>
146 #include <netdb.h>
147 #include <ifaddrs.h>
148 #include <stdio.h>
149 #include <stdlib.h>
150 #include <unistd.h>
151 #include <linux/if_link.h>
152 int main(int argc, char *argv[])
154 {
155 struct ifaddrs *ifaddr;
156 int family, s;
157 char host[NI_MAXHOST];
158 if (getifaddrs(&ifaddr) == -1) {
160 perror("getifaddrs");
161 exit(EXIT_FAILURE);
162 }
163 /* Walk through linked list, maintaining head pointer so we
165 can free list later. */
166 for (struct ifaddrs *ifa = ifaddr; ifa != NULL;
168 ifa = ifa->ifa_next) {
169 if (ifa->ifa_addr == NULL)
170 continue;
171 family = ifa->ifa_addr->sa_family;
173 /* Display interface name and family (including symbolic
175 form of the latter for the common families). */
176 printf("%-8s %s (%d)\n",
178 ifa->ifa_name,
179 (family == AF_PACKET) ? "AF_PACKET" :
180 (family == AF_INET) ? "AF_INET" :
181 (family == AF_INET6) ? "AF_INET6" : "???",
182 family);
183 /* For an AF_INET* interface address, display the address. */
185 if (family == AF_INET || family == AF_INET6) {
187 s = getnameinfo(ifa->ifa_addr,
188 (family == AF_INET) ? sizeof(struct sockaddr_in) :
189 sizeof(struct sockaddr_in6),
190 host, NI_MAXHOST,
191 NULL, 0, NI_NUMERICHOST);
192 if (s != 0) {
193 printf("getnameinfo() failed: %s\n", gai_strerror(s));
194 exit(EXIT_FAILURE);
195 }
196 printf("\t\taddress: <%s>\n", host);
198 } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
200 struct rtnl_link_stats *stats = ifa->ifa_data;
201 printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
203 "\t\ttx_bytes = %10u; rx_bytes = %10u\n",
204 stats->tx_packets, stats->rx_packets,
205 stats->tx_bytes, stats->rx_bytes);
206 }
207 }
208 freeifaddrs(ifaddr);
210 exit(EXIT_SUCCESS);
211 }
212
214 bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
215Linux man-pages 6.04 2023-03-30 getifaddrs(3)