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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 *ifap);

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 */
    u_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 */

ifa_next

Contains a pointer to the next structure on the list. This field is set to NULL in the last structure on the list.

ifa_name

Contains the interface name.

ifa_flags

Contains the interface flags, as set by ifconfig(8).

ifa_addr

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.)

ifa_netmask

References the netmask associated with ifa_addr, if one is set, otherwise it is NULL.

ifa_broadaddr

This 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.

ifa_dstaddr

This field, which should only be referenced for P2P interfaces, references the destination address on a P2P interface, if one exists, otherwise it is NULL.

ifa_data

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, ifa_data is NULL.

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

RETURN VALUES

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set 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(2), malloc(3), or sysctl(2).

SEE ALSO

ioctl(2), socket(2), sysctl(2), netintro(4), ifconfig(8)

HISTORY

The getifaddrs() function first appeared in BSDI BSD/OS. The function has been available on OpenBSD since OpenBSD 2.7.

BUGS

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