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getifaddrs, freeifaddrs

Get interface addresses.

#include <sys/types.h>
#include <sys/socket.h>
#include <ifaddrs.h>
getifaddrs(struct ifaddrs **ifap);

freeifaddrs(struct ifaddrs *ifp);


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 */
Contains a pointer to the next structure on the list. This field is NULL in last structure on the list.
Contains the interface name.
Contains the interface flags, as set by ifconfig utility.
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.)
References the netmask associated with ifa_addr, if one is set, otherwise it is NULL.
Should be referenced only for non-P2P interfaces, references the broadcast address associated with ifa_addr , if one exists, otherwise it is NULL
References the destination address on a P2P interface, if one exists, otherwise it is NULL.
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 contains a pointer to the struct ifa_data (as defined in include file <net/if.h>) which contains per-address interface statistics.

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


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

Return Values

The getifaddrs() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

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


Versions Link to
INtime 4.0 netlib.lib
See Also