指向结构数组的指针

Question

Consider I have the following C struct definitions:

struct StructA {
    int a;
    int b;
};

struct StructB {
    struct A *as;
    int count;
};

So, the as field of StructB points to an array of StructA 's of size count . Then, I represent struct StructA in Java with the following class:

public class StructA extends Structure {
    public int a;
    public int b;

    public StructA() {

    }

    public StructA(Pointer p) {
        super(p);
        read();
    }

    @Override
    protected List<String> getFieldOrder() {
        return Arrays.asList(new String[]{"a", "b"});
    }
    public static class Reference extends StructA implements Structure.ByReference { }
    public static class Value extends StructA implements Structure.ByValue { }
}

But, how would I represent struct B in Java? Since as is not a inline array, I would have to represent as as a Pointer , so how would I turn a Java StructA[] into a Pointer ?

Answer 1

You need to ensure that the field has pointer type. You can do this with Structure.ByReference (make a subclass of your structure class which implements the Structure.ByReference tagging interface) and then use Structure.toArray() to overlay a contiguous array of struct over that memory.

You can also just use a simple Pointer , but then you'll need to manually read/write the structure and related objects, as well as do native memory synchronization that JNA normally does for you.

For example:

class StructA {
    public static class ByReference extends StructA implements Structure.ByReference { }
}
class StructB {
   public StructA.ByReference sa;
   public int size;
   public StructA[] getMembers() {
       return (StructA[])sa.toArray(this.size);
   }
}