SWIG Python undefined symbol error

Question

I'm trying to create a *.so file for further use in Python using SWIG, but something isn't working.

I have two files: DataGatherer.h

#include <iostream>
#include <stdlib.h>
#include <time.h>
#include "gnublin.h"
#include <pthread.h>

class dataGatherer
{
    private:
    int threshold;
    int timeThreshold;
    int data[4096];
    bool running;
    gnublin_spi* spiDevice;
    pthread_t spiThread;
    void *params;

    public:

    dataGatherer(void);
    dataGatherer(int, int);
    void initData();
    int getThreshold(void);
    int* getData(void);
    int getPeak(void);
    void initSPI(void);
    void gatherData();

    void * run(void * arg);
    void stop(void);

    // for use of thread we have to implement some methods from C
    static void * start_static(void * params)
    {
        dataGatherer * thread_this = static_cast<dataGatherer*>(params);
        return thread_this->run(thread_this->params);
    }

    void start(void * params)
    {
        this->params = params;
        pthread_create(&spiThread, 0, &dataGatherer::start_static, this);
    }

};

and spiController.h

#include "dataGatherer.h"

class spiController
{
    private:
    bool runGather;
    dataGatherer* gatherer;
    int data[4096];

    public:
    spiController(void);
    spiController(int, int);
    void initData();
    bool checkStop();
    void stop();
    void start();
};

My spiController.i interface file looks like this:

/* spiController.i */
%module spiController
%{
#include "dataGatherer.h"
#include "spiController.h"
#include "gnublin.h"
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
extern void initData();
extern bool checkStop();
extern void stop();
extern void start();
%}

extern void initData();
extern bool checkStop();
extern void stop();
extern void start();

At the end I try to create the *.so file using commands in the terminal like in the example on the SWIG page with:

swig -python -c++ spiController.i
c++ -c spiController_wrap.c -I/usr/include/python2.7
c++ -shared spiController_wrap.o -o _spiController.so

*.cxx, *.o and *.so file are created with no error, but when I import the spiController into the python code I get:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "spiController.py", line 26, in <module>
    _spiController = swig_import_helper()
  File "spiController.py", line 22, in swig_import_helper
    _mod = imp.load_module('_spiController', fp, pathname, description)
ImportError: ./_spiController.so: undefined symbol: _Z9checkStopv

It's my first try using SWIG and I'm already stuck at this point. How can I resolve this?

Answer 1

You must link the library that defines your C++ functions that you have declared like checkStop etc. You would add -L<path to your C++ DLL> -l<name of your C++ DLL> on 3rd line of your example's compile steps.

Like this:

c++ -L<path to DLL> -l<name of your dll> -shared spiController_wrap.o -o _spiController.so