jna invokation problem

[colddew]

https://github.com/remram44/java-cpp-example/blob/master/java-jna/java/src/edu/nyu/cpptest/cpplib/MyClass.java

[root@SzfyTestServer backup]# java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Looking in classpath from sun.misc.Launcher$AppClassLoader@4e0e2f2a for /com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Found library resource at jar:file:/opt/backup/jna-5.5.0.jar!/com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Extracting library to /root/.cache/JNA/temp/jna15688228076106253.tmp
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Looking for library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so'
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Adding paths from jna.library.path: null
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Trying /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Found library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so' at /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'MyClass': /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so: undefined symbol: MyClass
        at com.sun.jna.Function.<init>(Function.java:252)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:594)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:570)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:556)
        at com.sun.jna.Library$Handler.invoke(Library.java:243)
        at com.sun.proxy.$Proxy0.MyClass(Unknown Source)
        at MyClass.<init>(MyClass.java:23)
        at MyClass.main(MyClass.java:35)

when i test this demo it throw the exception, i wonder if 「cpplib_shared」 is casual, or can i use another name?

the second problem is if 「MyClass_」prefix is necessary?

[remram44]

For JNA, the name of the lib and the functions can be changed, so long as it matches.

[remram44]

Your error message says it can't find the function MyClass, however there is no such function. I also just tried this with the current JNA (jna-5.5.0.jar) and it worked for me. Did you make changes to the code?

[colddew]

https://github.com/remram44/java-cpp-example/tree/master/cpplib

i use these c++ code to generate libcpplib.so, but when i use jna to invoke libcpplib.so, it can load libcpplib.so, but can not find the method name. also nm -D libcpplib.so show the method name are random strings

can you give me some advice, thx

[colddew]

java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass

i use this script, jna version is newest

[remram44]

Those are the C++ functions, which do get mangled. That is why I use a tiny wrapper (c_wrapper.cpp) with extern "C" functions which don't get mangled, and are the ones that get called from the Java wrapper class.

The alternative is to use Swig, which generates both wrapper for you.

[colddew]

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

public class MyClass {

    public interface CLibrary extends Library {

//        CLibrary INSTANCE = (CLibrary) Native.loadLibrary("cpplib_shared", CLibrary.class);
//        CLibrary INSTANCE = (CLibrary) Native.loadLibrary("cpplib", CLibrary.class);
        CLibrary INSTANCE = (CLibrary) Native.loadLibrary("/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so", CLibrary.class);

        Pointer MyClass_MyClass(int nb);

        int MyClass_getValue(Pointer self);

        void MyClass_increment(Pointer self);
    }

    private Pointer self;

    public MyClass(int nb) {
        self = CLibrary.INSTANCE.MyClass_MyClass(nb);
    }

    public int getValue() {
        return CLibrary.INSTANCE.MyClass_getValue(self);
    }

    public void increment() {
        CLibrary.INSTANCE.MyClass_increment(self);
    }

    public static void main(String[] args) {
        MyClass counter = new MyClass(3);
        counter.increment();
        counter.increment();
        System.out.println(counter.getValue());
    }
}

this is my java code

[colddew]

c++ code

https://github.com/remram44/java-cpp-example/blob/master/cpplib/include/cpplib/MyClass.h

#ifndef MYCLASS_H
#define MYCLASS_H

class MyClass {

private:
    int m_nb;

public:
    MyClass(int nb);
    int getValue() const;
    void increment();

};

#endif

https://github.com/remram44/java-cpp-example/blob/master/cpplib/src/MyClass.cpp

#include "cpplib/MyClass.h"

MyClass::MyClass(int nb)
  : m_nb(nb)
{
}

int MyClass::getValue() const
{
    return m_nb;
}

void MyClass::increment()
{
    m_nb++;
}

function MyClass exist

[remram44]

You need a wrapper, you can only call extern "C" functions, not classes or methods

[colddew]

i am not familiar with c++, and i change code like this and re-make, but i has the same error

extern "C"
{
#include "cpplib/MyClass.h"

MyClass::MyClass(int nb)
  : m_nb(nb)
{
}

int MyClass::getValue() const
{
    return m_nb;
}

void MyClass::increment()
{
    m_nb++;
}
}

[colddew]

Those are the C++ functions, which do get mangled. That is why I use a tiny wrapper (c_wrapper.cpp) with extern "C" functions which don't get mangled, and are the ones that get called from the Java wrapper class.

The alternative is to use Swig, which generates both wrapper for you.

ok, i get it, thank you very much

[colddew]

i replace MyClass.cpp with c_wrapper.cpp, and it throw another exception 「undefined symbol: _ZN7MyClassC1Ei」, how to solve this problem?

[root@SzfyTestServer build]# nm -D libcpplib.so 
0000000000201068 B __bss_start
                 w __cxa_finalize
0000000000201068 D _edata
0000000000201070 B _end
0000000000000a54 T _fini
                 w __gmon_start__
                 U __gxx_personality_v0
0000000000000818 T _init
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 w _Jv_RegisterClasses
00000000000009d0 T MyClass_ctor
0000000000000a1c T MyClass_getValue
0000000000000a36 T MyClass_increment
                 U _Unwind_Resume
                 U _ZdlPv
                 U _ZN7MyClass9incrementEv
                 U _ZN7MyClassC1Ei
                 U _ZNK7MyClass8getValueEv
                 U _Znwm

[root@SzfyTestServer backup]# java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Looking in classpath from sun.misc.Launcher$AppClassLoader@4e0e2f2a for /com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Found library resource at jar:file:/opt/backup/jna-5.5.0.jar!/com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Extracting library to /root/.cache/JNA/temp/jna5644361781661826174.tmp
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Looking for library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so'
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Adding paths from jna.library.path: null
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Trying /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Found library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so' at /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
java: symbol lookup error: /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so: undefined symbol: _ZN7MyClassC1Ei

[colddew]

i solve the problem, because i just compile c_wrapper.cpp and forget to compile MyClass.cpp

now , it works

[root@SzfyTestServer backup]# java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Looking in classpath from sun.misc.Launcher$AppClassLoader@4e0e2f2a for /com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Found library resource at jar:file:/opt/backup/jna-5.5.0.jar!/com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 1:23:01 AM com.sun.jna.Native extractFromResourcePath
INFO: Extracting library to /root/.cache/JNA/temp/jna5644361781661826174.tmp
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Looking for library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so'
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Adding paths from jna.library.path: null
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Trying /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Feb 13, 2020 1:23:01 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Found library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so' at /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
java: symbol lookup error: /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so: undefined symbol: _ZN7MyClassC1Ei
[root@SzfyTestServer backup]# java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass
Feb 13, 2020 2:05:20 AM com.sun.jna.Native extractFromResourcePath
INFO: Looking in classpath from sun.misc.Launcher$AppClassLoader@4e0e2f2a for /com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 2:05:20 AM com.sun.jna.Native extractFromResourcePath
INFO: Found library resource at jar:file:/opt/backup/jna-5.5.0.jar!/com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 13, 2020 2:05:20 AM com.sun.jna.Native extractFromResourcePath
INFO: Extracting library to /root/.cache/JNA/temp/jna1221045823503244492.tmp
Feb 13, 2020 2:05:20 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Looking for library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so'
Feb 13, 2020 2:05:20 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Adding paths from jna.library.path: null
Feb 13, 2020 2:05:20 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Trying /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Feb 13, 2020 2:05:20 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Found library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so' at /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
5