Thread: Java Native Access and arrays

I plan to write an interface for a spectrometer in JAVA. The manufacturer provides a c-dll to access the spectrometer. Therefore I have written a JNA-wrapper.

I could connect to the spectrometer and access simple methods of the dll. But I have problems to write appropriate functions, if the c-functions accept pointer-to-type arguments to return arrays.

For example:

c-header to access calibration data, from rcu1a.h:

USHORT WINAPI RC_ReadCalibrationValue(
	HANDLE DeviceHandle,
	double *DataArray
	);

according function in rcu1a.java:

short RC_ReadCalibrationValue(Pointer DeviceHandle, DoubleByReference DataArray);

and the code snipplet from Spectrometer.java, the class to access the spectrometer data:

private rcu1a lib = (rcu1a) Native.loadLibrary("rcu1a", rcu1a.class);
private DoubleByReference  calibData = new DoubleByReference();
 
//...
 
 public double [] calibrationData()
    {
 
       lib.RC_ReadCalibrationValue(DeviceHandle, calibData);
        return calibData.getPointer().getDoubleArray(0,6);
    }

The function should return an array with 6 calibration parameters. Like this I get and array out of bounds exception:

java.lang.IndexOutOfBoundsException: Bounds exceeds available space : size=8, offset=48

if I change to calibData.getValue(); I get the value that should be in the first field of the array.

Am I doing something substantially wrong in handling arrays?

Thx Richard