CODEWITHSUNDEEP
javac++java-native-interface
basickarl
basickarl

Reputation: 40541

Linking/using .so file in another

i have the following getmacip.cpp file with the following snipp code

// ...code

#include "test.h"

// ...code   

Test obj;
obj.printDem();

// ...code

here is the test.h file

#ifndef TEST_H
#define TEST_H
class Test
{
    public:
        void printDem();  
};
#endif

here is the test.cpp file

#include <iostream>
using namespace std;

void printDem()
{
    cout << "deus.ex.machina." << endl;
}

i am using java and c++ together via jni. i have gotten the file getmacip.cpp to work together with java and as you can see, i am trying to get the invoke the printDem() method from the getmacip.cpp file. i first compile the getmacip.cpp with the following:

g++ -fPIC -o libgetmacip.so -shared -I $JAVA_HOME/include -I $JAVA_HOME/include/linux getmacip.cpp -lc

this works fine. however when i do the same with test.cpp and run the program i get the error

/usr/lib/jvm/java-8-oracle/bin/java: symbol lookup error: /home/karl/workspace/sslarp/lib/libgetmacip.so: undefined symbol: _ZN4Test8printDemEv

i am obviously linking the files wrongly!

Upvotes: 0

Views: 87

Answers (2)

Severin Pappadeux
Severin Pappadeux

Reputation: 20130

You could check what kind of symbols are here

$ nm -D libgetmacip.so

will produce list of symbols

If you have to demangle C++ names, use c++filt

$ nm -D libgetmacip.so | c++filt

check "man nm" for info how symbols are marked/used

Upvotes: 1

user3159253
user3159253

Reputation: 17455

The definition of the printDem() doesn't belong to class Test.

Use

#include <iostream>
#include "test.h"
using namespace std;

void Test::printDem() {
    cout << "deus.ex.machina." << endl;
}

Also you should link the method definition into the shared library, something like this:

g++ -fPIC -o libgetmacip.so \
    -shared -I $JAVA_HOME/include -I $JAVA_HOME/include/linux \
        detmacip.cpp test.cpp

Also I should mention that raw JNI is a plain-C interface, that's all native calls are performed to functons declared as C functions (their implementation may use C++, check this tutorial. Also there's SWIG projects which helps to create required wrappers for C++ automa{g,t}ically.

Upvotes: 2

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