I am trying to just get basic things working in JNI... such as in this case being able to retrieve the value of an integer member from a native method of the same class. My java code initializes the integer member jInt to 0 and correctly prints out the results as 0. My native c dll however can access the field, but retrieves the wrong value of 647383456. Here is the output my program spits out...
Printing from Java...jInt has value: 0
Printing from c dll..Jint has value: 647383456
If anyone can tell anything I am doing wrong, I would greatly appreciate as this is even more greatly becoming a major source of frustration. I can tell that JNI is finding my integer field correctly because I get a "field could not be found" exception if I use a name other than jInt.
The following is source for my simple Java test program
public class Main
{
//Members
public int jInt = 0;
//Methods
native void CPrint();
void PrintJint()
{
System.out.println("Printing from Java...jInt has value: " + jInt + "\n");
}
public Main()
{
jInt = 0;
System.loadLibrary( "testnativeclr" );
jInt = 0;
}
//Entry Point
public static void main(String[] args)
{
Main main = new Main();
main.CPrint();
main.PrintJint();
}
}
Here is the source for my implementation of the native method CPrint located in the testnativeclr.dll.
#include <iostream>
#include "Main.h"
#include "jni.h"
using namespace std;
JNIEXPORT void JNICALL Java_Main_CPrint(JNIEnv* jEnv, jobject jObj)
{
jclass Object = jEnv->GetObjectClass( jObj );
jfieldID IntFieldId = jEnv->GetFieldID( Object, "jInt", "I" );
jint val = jEnv->GetIntField( Object, IntFieldId );
cout << "Printing from c dll..Jint has value: " << val << "\n";
}
Lastly here is Main.h which was generated by the Java binary command line tool javac..
/* DO NOT EDIT THIS FILE - it is machine generated */
#include "jni.h"
/* Header for class Main */
#ifndef _Included_Main
#define _Included_Main
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Main
* Method: CPrint
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_Main_CPrint
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
