C to CFFI 2

Here is the correct C Code:
#include <iostream>
#include <libusb.h>
using namespace std;

void printdev(libusb_device *dev); //prototype of the function

int main() {
	libusb_device **devs; //pointer to pointer of device, used to retrieve a list of devices
	libusb_context *ctx = NULL; //a libusb session
	int r; //for return values
	ssize_t cnt; //holding number of devices in list
	r = libusb_init(&ctx); //initialize a library session
	if(r < 0) {
		cout<<"Init Error "<<r<<endl; //there was an error
				return 1;
	}
	libusb_set_debug(ctx, 3); //set verbosity level to 3, as suggested in the documentation
	cnt = libusb_get_device_list(ctx, &devs); //get the list of devices
	if(cnt < 0) {
		cout<<"Get Device Error"<<endl; //there was an error
	}
	cout<<cnt<<" Devices in list."<<endl; //print total number of usb devices
		ssize_t i; //for iterating through the list
	for(i = 0; i < cnt; i++) {
				printdev(devs[i]); //print specs of this device
		}
		libusb_free_device_list(devs, 1); //free the list, unref the devices in it
		libusb_exit(ctx); //close the session
		return 0;
}

void printdev(libusb_device *dev) {
	libusb_device_descriptor desc;
	int r = libusb_get_device_descriptor(dev, &desc);
	if (r < 0) {
		cout<<"failed to get device descriptor"<<endl;
		return;
	}
	cout<<"Number of possible configurations: "<<(int)desc.bNumConfigurations<<"  ";
	cout<<"Device Class: "<<(int)desc.bDeviceClass<<"  ";
	cout<<"VendorID: "<<desc.idVendor<<"  ";
	cout<<"ProductID: "<<desc.idProduct<<endl;
	libusb_config_descriptor *config;
	libusb_get_config_descriptor(dev, 0, &config);
	cout<<"Interfaces: "<<(int)config->bNumInterfaces<<" ||| ";
	const libusb_interface *inter;
	const libusb_interface_descriptor *interdesc;
	const libusb_endpoint_descriptor *epdesc;
	for(int i=0; i<(int)config->bNumInterfaces; i++) {
		inter = &config->interface[i];
		cout<<"Number of alternate settings: "<<inter->num_altsetting<<" | ";
		for(int j=0; j<inter->num_altsetting; j++) {
			interdesc = &inter->altsetting[j];
			cout<<"Interface Number: "<<(int)interdesc->bInterfaceNumber<<" | ";
			cout<<"Number of endpoints: "<<(int)interdesc->bNumEndpoints<<" | ";
			for(int k=0; k<(int)interdesc->bNumEndpoints; k++) {
				epdesc = &interdesc->endpoint[k];
				cout<<"Descriptor Type: "<<(int)epdesc->bDescriptorType<<" | ";
				cout<<"EP Address: "<<(int)epdesc->bEndpointAddress<<" | ";
			}
		}
	}
	cout<<endl<<endl<<endl;
	libusb_free_config_descriptor(config);
}

Here is my partial translation into CFFI. I stopped where I got stuck: In the 'init' function 'devices' does not seem to be initialized correctly to an array of type libusb_device. I am looking for the right way to allocate pointers, pass pointers, or something else entirely that I missed.

(cffi:define-foreign-library libusb
  (:darwin (:or "libusb.dylib" "libusb-1.0.0.dylib"))
  (:unix (:or "libusb.so"))
  (t (error "unable to load libusb, unknown operating system")))

(cffi:use-foreign-library libusb)

(cffi:defcfun "libusb_init" :int (context :pointer))
(cffi:defcfun "libusb_set_debug" :void (context :pointer) (level :int))
(cffi:defcfun "libusb_get_device_list" :int (context :pointer) (devices :pointer))
(cffi:defcfun "libusb_get_device_descriptor" :int (device :pointer) (device-descriptor :pointer))

(cffi:defcstruct (libusb-device))
(cffi:defcstruct (libusb-device-descriptor :size 144)
  (b-num-configurations :uint8 :offset 136)
  (b-device-class :uint8 :offset 32)
  (id-vendor :uint16 :offset 72)
  (id-product :uint16 :offset 88))

(defun init ()
  (let ((devices (cffi:foreign-alloc :pointer))
	(context (cffi:foreign-alloc :pointer))
	(r 0)
	(cnt 0))
    (setf r (libusb-init context))
    (when (< r 0)
      (error "failed to initialize LIBUSB"))
    (setf cnt (libusb-get-device-list context devices))
    (when (< cnt 0)
      (error "Get Device Error"))
    (format t "~A Devices in list.~%" cnt)
    devices))

(defun print-dev (device-pointer)
  (let ((device-descriptor (cffi:foreign-alloc '(:struct libusb-device-descriptor)))
	(r 0))
    (setf r (libusb-get-device-descriptor device-pointer device-descriptor))
    (when (< r 0)
      (error "failed to get device descriptor"))
    (format t "Number of possible configurations: ~A~%"
	    (cffi:foreign-slot-value device-descriptor
				     '(:struct libusb-device-descriptor)
				     'b-num-configurations))
    (format t "Device Class: ~A~%"
	    (cffi:foreign-slot-value device-descriptor
				     '(:struct libusb-device-descriptor)
				     'b-device-class))
    (format t "Vendor ID: ~A~%"
	    (cffi:foreign-slot-value device-descriptor
				     '(:struct libusb-device-descriptor)
				     'id-vendor))
    (format t "Product ID: ~A~%"
	    (cffi:foreign-slot-value device-descriptor
				     '(:struct libusb-device-descriptor)
				     'id-product))))