How do I extract an array of `struct*` from a pointer to that array (in JNA)?

Question

I need to call a function with a signature like this:

size_t findDevices(devStruct_t **devs[]);

Some example C code uses the function like this:

devStruct_t **arrOfPointers;
size_t size;
size = findDevices(&arrOfPointers);
for(size_t i = 0; i < size; i++) {
    printf("devId:%d\n", arrOfPointers[i]->id);
}

How would I replicate the above code in Java using JNA?

I think the JNA function signature should look like this:

NativeLong findDevices(PointerByReference devs);

I can run this without crashing:

NativeLong size;
PointerByReference stdevs = new PointerByReference();
size = libstlink.stlink_probe_usb(stdevs);

But, I don't know how to access the structures.

Answer 1

You have the address of the start of the array in your "returned" pointer (stdevs.getValue()). Use that to extract the array of pointers, then initialize your structures from that.

Pointer[] ptrs = stdevs.getValue().getPointerArray(0, size.intValue());
DevStruct[] array = new DevStruct[size.intValue()];
for (int i=0;i < array.length;i++) {
    array[i] = new DevStruct(ptrs[i]);
}

public class DevStruct extends Structure {
    public DevStruct(Pointer p) {
        super(p);
        read();
    }
}