GETIFADDRS(3)

NAME
getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS
#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 stores a reference to a linked list of the network interfaces on the local machine in the memory referenced by ifap. The list consists of ifaddrs structures, as defined in the include file <ifaddrs.h>. The ifaddrs structure contains at least the following entries:

        struct ifaddrs   *ifa_next;         /* Pointer to next struct */
        char             *ifa_name;         /* Interface name */
        unsigned 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 */
        unsigned int      ifa_addrflags;    /* Address flags */

The ifa_next field contains a pointer to the next structure on the list. This field is NULL in last structure on the list.

The ifa_name field contains the interface name.

The ifa_flags field contains the interface flags, as set by ifconfig(8) utility.

The ifa_addr field references either the address of the interface or the link level address of the interface, if one exists, otherwise it is NULL. (The sa_family field of the ifa_addr field should be consulted to determine the format of the ifa_addr address.)

The ifa_netmask field references the netmask associated with ifa_addr, if one is set, otherwise it is NULL.

The ifa_broadaddr field, which should only be referenced for non-P2P interfaces, references the broadcast address associated with ifa_addr, if one exists, otherwise it is NULL.

The ifa_dstaddr field references the destination address on a P2P interface, if one exists, otherwise it is NULL.

The ifa_data field references address family specific data. For AF_LINK addresses it contains a pointer to the struct if_data (as defined in include file <net/if.h>) which contains various interface attributes and statistics. For all other address families, it is NULL.

The ifa_addrflags field contains the address flags, which are specific to the address family.

The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.

RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

EXAMPLES
The following example program prints a list of all addresses configured on the system.

    #include <sys/types.h>
    #include <sys/socket.h>
    #include <stdio.h>
    #include <ifaddrs.h>
    #include <util.h>
    #include <err.h>
    #include <stdlib.h>
    int
    main(int argc, char *argv[])
    {
    	struct ifaddrs *ifa, *a;
    	if (getifaddrs(&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;
    }

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

SEE ALSO
ioctl(2), socket(2), sysctl(3), networking(4), ifconfig(8)

HISTORY
The getifaddrs implementation first appeared in BSD/OS.

ifa_addrflags was added in NetBSD 8.0.

BUGS
If both <net/if.h> and <ifaddrs.h> are being included, <net/if.h> must be included before <ifaddrs.h>.