如何在JNA中传递包含原始类型数组的结构？

Question

I'm a novice JNA developer so please forgive me if this question is trivial, but I'm struggling against dealing with C-lang struct object including an array of float with JNA. Currently I got a compile error.

I think the problem is the wrong way to initialize and assign FloatByReference instance ( mys.Weights ) to mystruct class instance ( mys ), and believe that Java code below should not be modified because JNAerator automatically generated it.

My C Code:

typedef struct
{
  int n;
  float *Weights;
} mystruct;

void testfunc(mystruct* mys){
  printf(mys->Weights[0]);
}

public interface CLibrary extends Library {
    public static final String JNA_LIBRARY_NAME = "test";
    public static final NativeLibrary JNA_NATIVE_LIB = NativeLibrary.getInstance(CLibrary.JNA_LIBRARY_NAME);
    public static final CLibrary INSTANCE = (CLibrary)Native.loadLibrary(CLibrary.JNA_LIBRARY_NAME, CLibrary.class);

and Java:

public interface CLibrary extends Library {
    public static final String JNA_LIBRARY_NAME = "test";
    public static final NativeLibrary JNA_NATIVE_LIB = NativeLibrary.getInstance(CLibrary.JNA_LIBRARY_NAME);
    public static final CLibrary INSTANCE = (CLibrary)Native.loadLibrary(CLibrary.JNA_LIBRARY_NAME, CLibrary.class);


    public static class mystruct extends Structure {
        public int n;
        public FloatByReference Weights;
        protected List<? > getFieldOrder() {
            return Arrays.asList("n", "Weights");
        }
        public mystruct(int n, JnaeratorTestLibrary.feature_t.ByReference Features, FloatByReference Weights) {
            super();
            this.n = n;
            this.Features = Features;
            this.Weights = Weights;
        }
        public mystruct(Pointer peer) {
            super(peer);
        }
        public static class ByReference extends mystruct implements Structure.ByReference {

        };
        public static class ByValue extends mystruct implements Structure.ByValue {

        };
    };
    void testfunc(CLibrary.mystruct mys);
}

public static void main(String[] args) {
    mystruct mys = new mystruct();
    mys.n = 10;
    mys.Weights = new FloatByReference();
    // Compile error raises.
    mys.Weights = new float[4]; mys.Weights[0] = 1.0;

    testfunc(mys);
}

Compile Error message:

Type mismatch: cannot convert from float[] to FloatByReference

Answer 1

Use Pointer , then use Pointer.getFloatArray(0, n) to extract the data you want.

You'll need to allocate Memory and use Memory.write() to write a Java primitive float array to native memory before assigning that memory to your structure field.

FloatByReference is basically a pointer to one allocated float. JNAerator simply can't tell the difference between a pointer to a single float and a pointer to a buffer of floats (nor can a human without some additional context).