Hi, I don't understand why my loop crashes, Here is my grovel definition for ifaddrs struct: (cstruct ifaddrs "struct ifaddrs" (next "ifa_next" :type :pointer) (name "ifa_name" :type :string) (flags "ifa_flags" :type :unsigned-int) (address "ifa_addr" :type :pointer) (netmask "ifa_netmask" :type :pointer) (broadcast "ifa_broadaddr" :type :pointer) (point-to-point-destination "ifa_dstaddr" :type :pointer) (data "ifa_data" :type :pointer)) Here is my loop, i was expecting next to be a null pointer after the first vmnet8 CL-USER> (cffi:with-foreign-object (p :pointer) (getifaddrs p) (do () ((cffi:null-pointer-p p)) (format t "Interface: ~a~%" (cffi:foreign-slot-value (cffi:mem-ref p :pointer) 'ifaddrs 'name)) (setf p (cffi:foreign-slot-value p 'ifaddrs 'next)))) Interface: lo Interface: sit0 Interface: eth0 Interface: wlan0 Interface: vmnet1 Interface: vmnet8 Interface: lo Interface: wlan0 Interface: vmnet1 Interface: vmnet8 Interface: lo Interface: wlan0 Interface: vmnet1 Interface: vmnet8 ; Evaluation aborted on #<SB-SYS:MEMORY-FAULT-ERROR {BF604E1}>. Regards, Jose