Mapping const char** to Java type with JNA

Question

I am trying to use a C++ library in Java with JNA. In the header file of the library I have the following method declaration:

extern "C" void foo(const char** bar);

The paramterer bar should be passed to foo empty, and foo vill assign it a value that I want to retreive in Java. How should the corresponding Java method declaration be set up (e.g. what Java type should I map bar to), and how can I use it?

I have tried the following Java declarations:

void foo(String bar);
void foo(String[] bar);
void foo(Pointer bar);

They all result in the following error when I call foo:

Exception in thread "main" java.lang.Error: Invalid memory access

Answer 1

Find below a small snippet.

libfoo.cpp

#include <stdio.h>
extern "C" void foo(const char** bar);

void foo(const char** bar) {
    for (int i = 0; bar[i] != '\0'; i++) {
        fprintf(stdout, "%s\n", bar[i]);
    }
}

LibFooDemo.java

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

public class LibFooDemo {

    public interface FooLibrary extends Library {
        FooLibrary INSTANCE = (FooLibrary)
                Native.loadLibrary("foo", FooLibrary.class);
        void foo(String[] format);
    }

    public static void main(String[] args) {
        String[] vals = {"foo", "bar", "foobar"};
        FooLibrary.INSTANCE.foo(vals);
    }
}

compile all sources

gcc -c -fPIC libfoo.cpp -o libfoo.o
gcc -shared -o libfoo.so  libfoo.o
javac -cp jna-4.2.1.jar LibFooDemo.java

run the Java program

java -Djava.library.path=. -cp jna-4.2.1.jar:. LibFooDemo

output

foo
bar
foobar