JNI problem, pasing String to native (C function) by reference

[Marko Filipovic]

How can I pass String type from java to C by reference, in other words I want inout String parametar but i have a problem
how to assign it's value in c++ and to see this changes back in Java?

[Travis Hein]

I don't know how to do that with a string parameter in JNI, Strings themselves are immutable.

even in Java, we can not

// some java function
public void aFunction(String input) {
  input = "other message";
}


public void run() {
  String aString = "where's the beef";

  aFunction(aString);

  System.out.println(aString); /// is going to show the original message before the aFunction() call
}

now you could pass an object (structure) into the JNI function., or an array of strings.

Here is an example of this on sun's forum http://forums.sun.com/thread.jspa?threadID=5395533

[Marko Filipovic]

Travis Hein wrote:I don't know how to do that with a string parameter in JNI, Strings themselves are immutable.

even in Java, we can not

// some java function
public void aFunction(String input) {
  input = "other message";
}


public void run() {
  String aString = "where's the beef";

  aFunction(aString);

  System.out.println(aString); /// is going to show the original message before the aFunction() call
}

now you could pass an object (structure) into the JNI function., or an array of strings.

Here is an example of this on sun's forum http://forums.sun.com/thread.jspa?threadID=5395533

Jea right, I forgot about that this was a realy stupid question, my profesor told me yesterday the same
Ok I'll try to pass the char array... Thanks anyway

[salvin francis]

just out of curiosity, does it work for chars ?
I mean you have a char array in java, you sent it to C program which changes this array,
is it reflected back into the java program ?

[Marko Filipovic]

salvin francis wrote:just out of curiosity, does it work for chars ?
I mean you have a char array in java, you sent it to C program which changes this array,
is it reflected back into the java program ?

string keyStr=CreateKeyStr();
jchar * recivedNative=jniEnv->GetCharArrayElements(recived,0);
CJavaCPPFunctions::CharArray2JcharArray(jniEnv,recivedNative,keyStr.c_str());
jniEnv->ReleaseCharArrayElements(recived,recivedNative,0);

void CJavaCPPFunctions::CharArray2JcharArray(JNIEnv * jniEnv,jchar * outJcharArray,const char * charArray){
	
	int len=strlen(charArray);
	for (int i = 0; i < len; i++) {
              outJcharArray[i] = (jchar)charArray[i];
        }
}

yes it's works just fine
in c++ code I just copy chars from my function result to inout chararray parameter and it's is changes char[] back in Java..
but there is a small problem only... I must give the size of array in java which in c++ is not nessery...

Du you know how to define dynamic array in Java something like char[] array = new char[] ?
(is it posible without char[] array = new char[ARRAY_SIZE]) )

[salvin francis]

clueless,


but i guess you could use multidimensional arrays for that ?