JNA结构参考

Question

below the method and the unit test for that method. The problem is that I'm not able to return the value of result from the Load method. the unit test below fails!

I thought that by default JNA's object were ByRef by default so I tried instantiating and passing LoadResults "without" .ByReference ...

where is my mistake?

@Test
public void testLoad () {
   MY_Processor proc = new MY_Processor();
   // LoadResults result = new LoadResults ();
   LoadResults.ByReference result = new LoadResults.ByReference();
   ByteByReference [] pathToFile = new ByteByReference[256];
   // fill pathToFile out ... 

   try {
      proc.Load (pathToFile, result);
      assertEquals(0, result.errorCode);
      assertEquals(1, result.elaborationTime);
      assertEquals(2, result.coreItem);
   } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
   }
}



public Integer Load ( ByteByReference[] pathToFile, 
                          LoadResults.ByReference result ) throws Exception {

   // here result is correctly filled out !
   LoadResults result = null;
   result = native.getResult (numCore);
}

added the native code.

UPDATE

// header
typedef struct
{
   int     errorCode;
   int     elaborationTime;
   int     coreItem;
} LoadResults;

//[in]  path
//[out] result
int Load (char path[MY_BUFFER_DEFINE], LoadResults* result);

// implementation ...

LoadResults* getResult (int numCore)
{
   // some check ... 

   LoadResults *localResult = new LoadResults();
   // fill out ... 

   return localResult;
}

there is a "free" method exposed by the native code but I didn't show in order to keep the focus on my problem :-)

/UPDATE

thanks!

O.

Answer 1

The problem is that you're passing a Structure as a parameter, then reassigning that parameter within the function. That will have no effect whatsoever on the argument.

The pattern you need to follow is this:

Pointer p = mylib.getResult()
MyStructure m = new MyStructure(p);
// ....
mylib.free(p);

I'd recommend you pass in a native string ( const char* ) as your path rather than a fixed-size buffer of native char .

UPDATE

If you want to copy a result into the argument, then you'll need to copy the structure's contents, eg

public int Load(LoadResults arg) throws Exception {
    // Effectively copy memory from result into arg
    LoadResults result = native.getResult(numCore);
    if (alternative_1) {
        // Copy result's native memory into arg's memory, then sync Java fields
        result.useMemory(arg.getPointer());
        result.write();
        arg.read();
    }
    else {
        // Sync result's native memory with arg's Java fields
        Pointer p = arg.getPointer();
        arg.useMemory(result.getPointer());
        arg.read();
        arg.useMemory(p);
    }
}

Answer 2

Just solved ...

1) I don't need to use LoadResults.ByReference .

2) the problem was that into the Load method I updated the reference passed in input with another one:

public Integer Load ( ByteByReference[] pathToFile, LoadResults result ) throws Exception     
{
   // that's the problem!!!! storing the value into another object with another "address"
   // and not the original "results".
   // result = native.getResult (numCore);

   // solved with this:
   native.getResult (numCore, result);
}