Copying jobjectarray to CString[] with JNI

For the first one, i do not want to add each char to the jobjectArray, i want each string, CString[] arr = new CString[] {"this", "is", "a", "string", "array"};  Can you post good code to accomplish this?

I am trying out your other code changes and will get back to you!

Thanks!

<This _should_ really be continued in only 1 thread; jsm11482, which thread do you wish to continue this in? C++ or Java?>

>>>> For the first one, i do not want to add each char to the jobjectArray,

//CString array to jobjectArray

jobjectArray JNIUtil::CopyArray(JNIEnv* env, CString in[], int siz)
{
     jobjectArray out = env->NewObjectArray(siz, env->FindClass("java/lang/String"), NULL);

     for (int i = 0; i < siz; i++)
          env->SetObjectArrayElement(out, i, env->NewStringUTF(in[i]));

     return out;
}

'CString in[]' is equivalent to CString* but you easier can see that it is an array of CStrings. The size of the array can't be detected from the argument as it turned to a pointer (size is always 4) when passed as an argument. So, you would need an additional argument as it would be with any C array. As an alternative you might use std::vector<CString> or CStringArray that were container classes with a size() or GetSize() function.

jobjectArray JNIUtil::CopyArray(JNIEnv* env, CStringArray in)
{
     jobjectArray out = env->NewObjectArray(in->GetSize(), env->FindClass("java/lang/String"), NULL);

     for (int i = 0; i < in.GetSize(); i++)
          env->SetObjectArrayElement(out, i, env->NewStringUTF(in[i]));

     return out;
}

Regards, Alex


>>>> This _should_ really be continued in only 1 thread

As it is C++ code that is required I would suggest to let the solution here in C++ TA.

The Java thread may be closed as well as the maximum points for one question is not exceeded.

correction:

jobjectArray JNIUtil::CopyArray(JNIEnv* env, const CStringArray& in)
{
     jobjectArray out = env->NewObjectArray(in.GetSize(), env->FindClass("java/lang/String"), NULL);

     for (int i = 0; i < in.GetSize(); i++)
          env->SetObjectArrayElement(out, i, env->NewStringUTF(in[i]));

     return out;
}

please continue this thread in the C++ area

ok so if i send a double array of {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} i am getting back an array of (| delimited):
0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|4.9E-324|-999.0|-999.0|-999.0|-999.0|-999.0|-999.0|0.0|0.05|1.0|0.0|1.0|0.0|0.0|0.0|0.0|1.016208805E-315|0.045|0.0|0.0|1.4967570022479021E-249|2.7585945288E-313|0.0|0.0|1.4784031306360101E-249|1.06099789573E-313|1.2288611814499066E-249|1.9199678765E-313|4.4E-323|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|0.0|2.0|1.016208805E-315|0.03|0.04|0.0|1.537211390420101E-249|2.223731269E-314|1.5372071280969523E-249|2.121995796E-314

trace:
calc.setPctSharesVestArray(new double[]  {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
-> to C++ DLL convert jobjectArray to double array

calc.setPctSharesVestArray()
-> to C++ DLL convert double array to jobjectArray

returns the long array above (after making the suggested code changes)

>>>> calc.setPctSharesVestArray(new double[]  {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});

The code above isn't valid C++ code.

Please, post the original call that failed (plus array creation) and the code of the function that does the conversion( should be JNIUtil::CopyArray).

Regards, Alex

The line: calc.setPctSharesVestArray(new double[]  {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});

is run in java via JNI, the array is passed to the following C++ function:

JNIEXPORT void JNICALL Java_com_towers_ltip_LTIPCalc_setPctSharesVestArray (JNIEnv *env, jobject obj, jint ptr, jdoubleArray value)
{
      CLTIPCalc* calc = (CLTIPCalc*)ptr;
      JNIUtil* util = new JNIUtil();

      util->CopyArray(env, value, calc->m_adPctSharesVest);
}

i just want to copy the passed-in jdoubleArray to the member variable m_adPctSharesVest.

Sorry for the confusion.

>>>> Sorry for the confusion

No problem, but I need both the class/struct definition of CLTIPCalc and the code of JNIUtil::CopyArray.

You always should be aware that C++ needs allocation if handling with plain C arrays rather than with container classes.

Regards, Alex

Definition of variable in CLTIPCalc:
    double m_adPctSharesVest[11];

JNIUtil::CopyArray definitions:

//jdoubleArray to double[]
void JNIUtil::CopyArray(JNIEnv* env, jdoubleArray inObj, double* out)
{
      jdouble* in = env->GetDoubleArrayElements(inObj, FALSE);
      int size = env->GetArrayLength(inObj);

      if (size > 0)
      {
            out = new double[size];

            for (int i = 0; i < size; i++)
                  out[i] = in[i];
      }
      else
            out = NULL;
}


and then....
//double[] to jdoubleArray
jdoubleArray JNIUtil::CopyArray(JNIEnv*env, double* in, int size)
{
      jdoubleArray out = env->NewDoubleArray(size);

      env->SetDoubleArrayRegion(out, 0, size, in);

      return out;
}

>>>> void JNIUtil::CopyArray(JNIEnv* env, jdoubleArray inObj, double* out)

That is wrong cause we need to return 'out' pointer but were changing it locally only.

Either change to

    void JNIUtil::CopyArray(JNIEnv* env, jdoubleArray inObj, double*& out)

Then out pointer was returned. Or - maybe better -

double* JNIUtil::CopyArray(JNIEnv* env, jdoubleArray inObj)
{
    jdouble* in = env->GetDoubleArrayElements(inObj, FALSE);
     int size = env->GetArrayLength(inObj);

     double out* = NULL;
     if (size > 0)
     {
          out = new double[size];

          for (int i = 0; i < size; i++)
               out[i] = in[i];
     }

     return out;
}

Regards, Alex
 

correction:

I saw that you already have an allocation for the double array. So, you could change the code to

jdoubleArray to double[]
void JNIUtil::CopyArray(JNIEnv* env, jdoubleArray inObj, double* out)
{
     jdouble* in = env->GetDoubleArrayElements(inObj, FALSE);
     int size = env->GetArrayLength(inObj);

     if (size > 0 && size <= 11)
     {
          for (int i = 0; i < size; i++)
               out[i] = in[i];
     }
}

Returning a pointer is senseful only if you would change the array in the struct CLTIPCalc to a pointer initialized by NULL. Then, you would call like

   calc->m_adPctSharesVest = util->CopyArray(env, value );

Regards, Alex

>>>> Definition of variable in CLTIPCalc:
>>>>    double m_adPctSharesVest[11];

Did you initialize the array somehow? You could do it in a constructor:


   CLTIPCalc::CLTIPCalc()
   {
     memset(m_adPctSharesVest, 0, sizeof(m_adPctSharesVest));
     // init other members or use an initialiser list

  }

Or - maybe simpler - initialize the struct when creating an instance:

   CLTIPCalc any = { 0 };  // make all zero

Note, that can't be done if there are class members.

Regards, Alex

it is initialized as a static array in the header file: double m_adPctSharesVest[11];

Seems OK, I ended up using a solution not posted here. Thank you.

>>>> Seems OK, I ended up using a solution not posted here. Thank you.

I made at least 6 comments with valid C++ code responding to various additional questions made by jsm11482.

If the questioner doesn't honour that, I don't want points, but a refund isn't appropriate, especially as there is no open question left - as far as I can see.

Regards, Alex