Hello.

I'm trying to connect a fingerprint device to a Java app using libfprint (http://reactivated.net/fprint/). I've come a long way but have now hit a roadblock. I'm new to JNA, so please excuse any obvious errors.

I have a C function, enroll(), that returns the fingerprint data as a struct fp_print_data to my Java app that stores this data in a fp_print_data object, this object is then stored for later identification. Function, struct and object definitions are listed below. This part works fine, I think :)

Now I want to take this stored print and compare this to a freshly scanned print. This is done by sending an array of fp_print_data Structures to a C function called identify(). identify() then returns the index of the print in the array that matched the freshly scanned print. The problem is that I get a segmentation fault. If I pass empty fp_print_data objects to the function I don't get the seg fault so I guess I have a problem with my fp_print_data Structure. It also works fine if I leave out the Java app all together and let a C program do all the work. My guess is that the array of Structures I send to idenfity() is not allocated correctly. I'd appreciate any help I can get :)

C: struct fp_print_data { uint16_t driver_id; uint32_t devtype; enum fp_print_data_type type; size_t length; unsigned char data[0]; };

struct fp_print_data* enroll (void){ // print_data is a globally defined struct fp_print_data* fp_enroll_finger(sel_dev, &print_data); }

size_t* identify(struct fp_print_data **print_gallery, int prints){ size_t *match_offset = -1; int result = -1; print_gallery[prints] = NULL; // The list must be NULL terminated fp_identify_finger(sel_dev, print_gallery, &match_offset); return match_offset; }

Java: public class fp_print_data extends Structure {

public int driver_id; public int devtype; public int type; public int length; public IntByReference data; }

public static void main(String[] args){ fp_print_data enrolledPrint = myLibrary.INSTANCE.enroll(); // The array must be NULL-terminated, thus I need to allocate one extra element Structure[] printGallery = enrolledPrint.toArray(2); myLibrary.INSTNCE.identify(printGallery, printGallery.length-1); }