load lib .so with jna

Question

I am actually trying to open a library. So (I did it in c++) with JNA my problem is that I can not open a library when there is a static variable. However I have to use un singleton in my library so I am looking for why a static variable can not be use with JNA to prove it a made a little library

there is the .h file:

#ifndef UNTITLED1_LIBRARY_H
#define UNTITLED1_LIBRARY_H
#include <iostream>
class library {
 private:
  static char* h;
 public:
  int hello();
};

extern "C" int hello(){
 library lib;
 return lib.hello();
}

#endif

then my .cpp file:

#include "library.h"
#include "ecrire.h"

#include <iostream>

int library::hello() {
 h = (char*)"hello world";
 std::cout<<h<<std::endl;
 return 45;
}

then my java class and interface

public class Westgard {
static {       
    System.setProperty("jna.library.path","../logic/resources/calculator"); 
}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    int maj = InterfaceLibWestgard.INSTANCE.hello();
    System.out.println(maj);
}

}


import com.sun.jna.Library;
import com.sun.jna.Native;

public interface InterfaceLibWestgard extends Library {
  int hello();
  static InterfaceLibWestgard INSTANCE = (InterfaceLibWestgard) 
  Native.loadLibrary("../logic/resources/calculator/libuntitled1.so", 
  InterfaceLibWestgard.class);
}

So if I try like this it wont work but when a remove the static from the .h it works does not anyone know why I have been looking for since 4-5 hours still do not know why...

This is my issue log:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Unable to load 
 library '../logic/resources/calculator/libuntitled1.so': Native library 
(linux-x86-64/../logic/resources/calculator/libuntitled1.so) not found in 
resource path ([file:/opt/java/jdk1.8.0_151/jre/lib/resources.jar, 

Answer 1

You have declared library::h but not defined it. You need to add

char* library::h = 0;

in your cpp file.

Presumably the library is either failing to compile or it is compiling but expecting this missing symbol to be defined in another library.