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FreeBSD 11.0 - man page for freeifaddrs (freebsd section 3)

GETIFADDRS(3)						   BSD Library Functions Manual 					     GETIFADDRS(3)

NAME
getifaddrs -- get interface addresses
SYNOPSIS
#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 fol- lowing 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 */ 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 in a pointer to the struct if_data (as defined in include file <net/if.h>). For AF_LINK addresses, it contains various interface attributes and statistics. For all other address families, it contains per-address inter- face statistics. The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.
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 indi- cate the error.
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 BSDi BSD/OS.
BUGS
If both <net/if.h> and <ifaddrs.h> are being included, <net/if.h> must be included before <ifaddrs.h>.
BSD
November 25, 2014 BSD