结构内部的JNA结构

Question

I am quite new to JNA programming. I have a native code as below

int Data(int Number, aaa *Data, int* error);

typedef struct {
    uint8 Storage;
    LStr path;
    int32 chart;
    int32 strt;
    LStr val;
    int32 timedata;
    } aaa;

typedef struct {
    int32   cnt;    /*num of bytes that follow*/    
    uChar   str[1]; 
} LStrval, *LStrPtr, **LStr;

How can I call this native function from Java using JNA. I tried several options, but I am not getting the results. one of the options I tried is below.

the interface function

public int SetStorage_Data(int num,Storage_Data.ByReference data, Pointer error);

 public class Storage_Data extends Structure{
        public static class ByReference extends Storage_Data implements Structure.ByReference {}

        public byte storage;
        public Stringtype.ByReference savepath;
        public int chart;
        public int strt;
        public Stringtype.ByReference val;
        public int timedata;

        @Override
        protected List getFieldOrder() {
            return Arrays.asList("storage", "savepath","chart",
                    "strt","val","timedata");
        }
    }



public class Stringtype extends Structure{
        public static class ByReference extends Stringtype implements Structure.ByReference {

            public ByReference(int buffersize) {
                super(buffersize);
                // TODO Auto-generated constructor stub
            }}

        public int count;
        public byte[] str;

        public Stringtype(int buffersize) {
            str = new byte[buffersize];
            count = str.length;
            allocateMemory();
        }

        @Override
        protected List getFieldOrder() {
            return Arrays.asList("count", "str");
        }
    }

And the Java call

InjectionAnalyzerInterfaces.Storage_Data.ByReference storagedata = new InjectionAnalyzerInterfaces.Storage_Data.ByReference();

 int len= string.length;
 InjectionAnalyzerInterfaces.Stringtype.ByReference savepath = new InjectionAnalyzerInterfaces.Stringtype.ByReference(len);

            byte[] stringbyte = string.getBytes();
            System.arraycopy(stringbyte, 0, savepath.str, 0, bytes);
            storagedata.savepath = savepath;
            storagedata.chart = 1;
            storagedata.strt =1;
            String temp= "all";
            byte[] strtbyte = temp.getBytes();
            int dd = strtbyte.length;
            InjectionAnalyzerInterfaces.Stringtype.ByReference stra = new InjectionAnalyzerInterfaces.Stringtype.ByReference(dd);
            System.arraycopy(strtbyte, 0,  stra.str,0, dd);
            storagedata.strt = stra;


            storagedata.tdata = 0;

            Pointer error = new Memory(5);

            int status1 =  lib.Set_Config_Storage_Data(deviceNumber, storagedata, error);

Please do help me. Thank you in advance

Answer 1

In defining your LStrVal , you need to initialize the primitive array field so that JNA knows how much memory to allocate (at least to start with):

public byte str = new byte[1];

You need to override Structure.read() to do the right thing, and provide a Pointer -based constructor to read after initializing from native memory:

public void read() {
    count = (int)readField("count");
    str = new byte[count];
    super.read();
}

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

Finally, your containing struct has struct** fields (no idea why), which you'll have to map to Pointer , and provide a convenience function to actually convert to your desired structure:

public Pointer savepath;
public LStr getSavepath() {
    return savepath != null ? new LStr(savepath.getPointer(0)) : null;
}

Answer 2

You're on the right track.

You need to declare the inner structure ( LStrVal ) as its own structure class. It looks like you've done that with your Stringtype structure but you need to change a few things there:

• Get rid of the constructor with the int arg. Your C structure specifies the size of the byte[] array as 1, just use that constant.
• You need a no-arg constructor that calls super()
• You need a constructor with a Pointer arg p that calls super(p)
• You don't need the ByReference parts

Then the outer structure you should use a PointerByReference type for those structure pointers, and then in your main code, use new Stringtype(pbr.getValue()) to convert the pointer into the necessary class.

Alternately, as @technomage suggests, you could use a Pointer type, and then instead of getValue() you'd use getPointer(0) . Bottom line is that you need a pointer (to a pointer) as your instance variable.