C Function Pointer Wrapping Example not working

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  • Charlie
    #1

    C Function Pointer Wrapping Example not working

    Hi All,

    I am new to using swig/C++/python. I got some problem with function
    pointers. I posted in swig-user, but got no response. So I forwarded
    it here. You help is greatly appreciated.

    Thanks!

    ---------- Forwarded message ----------

    Hi All,

    Yesterday I posted about the question I had of template function. This
    time I worked step step from examples in Doc 1.3 to reach my ultimate
    goal. But as I worked on the Function Pointer Example in 5.4.9 in Doc
    1.3, it doesn't work. My platform is a Ubuntu linux with swig 1.3.36,
    python 2.5.2 and gcc 4.2.3.

    The compiling and linking has no errors:

    swig -python -c++ -o test_wrap.cpp test.i
    python setup-test.py build
    running build
    running build_py
    copying test.py -build/lib.linux-i686-2.5
    running build_ext
    building '_test' extension
    gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -
    Wstrict-prototypes -fPIC -I/usr/include/python2.5 -c test_wrap.cpp -o
    build/temp.linux-i686-2.5/test_wrap.o
    cc1plus: warning: command line option "-Wstrict-prototypes" is valid
    for Ada/C/ObjC but not for C++
    g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions build/temp.linux-
    i686-2.5/test_wrap.o build/temp.linux-i686-2.5/test.o -o build/
    lib.linux-i686-2.5/_test.so

    But when I try to import test in python, it complains:
    import _test
    ImportError: ./_test.so undefined symbol: _Z9binary_opiiP FiiiE

    My test.i is:
    %module test
    %{
    #include "test.h"
    %}
    %include "test.h"

    %callback("%s_c b");
    int add( int, int ); //add_cb
    int sub( int, int ); //sub_cb
    int mul( int, int ); //mul_cb
    %nocallback;

    My test.h is:

    int binary_op(int a, int b, int (*op)(int,int) );
    int add( int a, int b ) { return a+b; }
    int sub( int a, int b ) { return a-b; }
    int mul( int a, int b ) { return a*b; }
    // NOTE: this is func ptr from example in Doc 1.3: 5.4.9

    It is really strange to me. I am a novice swigger but I really need
    its power to accelerate my development. Could anybody point out where
    my problem is?

    TIA

    Charlie
    Tags: None
    • Nick Craig-Wood
      #2
      Re: C Function Pointer Wrapping Example not working

      Charlie <Charlie.Xia.FD U@gmail.comwrot e:
      I am new to using swig/C++/python. I got some problem with function
      pointers. I posted in swig-user, but got no response. So I forwarded
      it here. You help is greatly appreciated.
      >
      Thanks!
      >
      >
      Hi All,
      >
      Yesterday I posted about the question I had of template function. This
      time I worked step step from examples in Doc 1.3 to reach my ultimate
      goal. But as I worked on the Function Pointer Example in 5.4.9 in Doc
      1.3, it doesn't work. My platform is a Ubuntu linux with swig 1.3.36,
      python 2.5.2 and gcc 4.2.3.
      >
      The compiling and linking has no errors:
      >
      swig -python -c++ -o test_wrap.cpp test.i
      python setup-test.py build
      running build
      running build_py
      copying test.py -build/lib.linux-i686-2.5
      running build_ext
      building '_test' extension
      gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -
      Wstrict-prototypes -fPIC -I/usr/include/python2.5 -c test_wrap.cpp -o
      build/temp.linux-i686-2.5/test_wrap.o
      cc1plus: warning: command line option "-Wstrict-prototypes" is valid
      for Ada/C/ObjC but not for C++
      g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions build/temp.linux-
      i686-2.5/test_wrap.o build/temp.linux-i686-2.5/test.o -o build/
      lib.linux-i686-2.5/_test.so
      >
      But when I try to import test in python, it complains:
      import _test
      ImportError: ./_test.so undefined symbol: _Z9binary_opiiP FiiiE
      The above is a mangled name so you've got some C vs C++ problems I'd
      say.

      You could try putting some extern "C" {} in around all the functions
      which are imported and exported. Have a look at the code SWIG
      generates and see if it puts some extern "C" in and match what it
      does in your code.

      We used to use SWIG in for python embedding in our C++ project, but we
      found that using ctypes is a lot easier. You just write C .so/.dll
      and use ctypes to access them. You can do callbacks and embedding
      python like this too.

      --
      Nick Craig-Wood <nick@craig-wood.com-- http://www.craig-wood.com/nick

        Comment

        • Charlie
          #3
          Re: C Function Pointer Wrapping Example not working

          >
           But when I try to import test in python, it complains:
           import _test
           ImportError: ./_test.so undefined symbol: _Z9binary_opiiP FiiiE
          >
          The above is a mangled name so you've got some C vs C++ problems I'd
          say.
          >
          You could try putting some extern "C" {} in around all the functions
          which are imported and exported.  Have a look at the code SWIG
          generates and see if it puts some extern "C" in and match what it
          does in your code.
          >
          We used to use SWIG in for python embedding in our C++ project, but we
          found that using ctypes is a lot easier.  You just write C .so/.dll
          and use ctypes to access them.  You can do callbacks and embedding
          python like this too.
          Thanks Nick.

          I tried your method, if I am right(please see the attached details),
          and I still got the undefined symbol error like previous. The only
          difference is "_Z9binary_opii PFiiiE" changed to "binary_op" . Could you
          help me more on this. It seems to have a mixed problems here and I
          guess what you've pointed out is one of them. But really, what I do
          now is just try to reproduce the example, how can this fails? What my
          ultimate need is wrapping up a template function taking template
          function pointer as argument. Did you ever try that? Many thanks
          already anyway.

          FILE and ERROR details:

          ---------test.i--------------
          %module test
          %{
          #include "test.h"
          %}
          %include "test.h"

          %callback("%s_c b");
          int myadd( int, int ); //myadd_cb
          int mysub( int, int ); //mysub_cb
          int mymul( int, int ); //mymul_cb
          %nocallback;
          --------------------------------

          -----------test.h--------------
          extern "C"{
          int binary_op(int a, int b, int (*op)(int,int) );
          int myadd( int a, int b ) { return a+b; };
          int mysub( int a, int b ) { return a-b; };
          int mymul( int a, int b ) { return a*b; };
          }
          ---------------------------------

          ------error message----------
          Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
          File "test.py", line 7, in <module>
          import _test
          ImportError: ./_test.so: undefined symbol: binary_op
          ----------------------------------

          -------compiling message-----
          swig -v -python -c++ -o test_wrap.cpp test.i
          LangSubDir: python
          Search paths:
          ./
          ./swig_lib/python/
          /usr/local/share/swig/1.3.36/python/
          ./swig_lib/
          /usr/local/share/swig/1.3.36/
          Preprocessing.. .
          Starting language-specific parse...
          Processing types...
          C++ analysis...
          Generating wrappers...
          python setup-test.py build
          running build
          running build_py
          copying test.py -build/lib.linux-i686-2.5
          running build_ext
          building '_test' extension
          gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -
          Wstrict-prototypes -fPIC -I/usr/include/python2.5 -c test_wrap.cpp -o
          build/temp.linux-i686-2.5/test_wrap.o
          cc1plus: warning: command line option "-Wstrict-prototypes" is valid
          for Ada/C/ObjC but not for C++
          g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions build/temp.linux-
          i686-2.5/test_wrap.o build/temp.linux-i686-2.5/test.o -o build/
          lib.linux-i686-2.5/_test.so
          ---------------------------------

            Comment

            • Aaron Brady
              #4
              Re: C Function Pointer Wrapping Example not working

              On Nov 16, 8:56 pm, Charlie <Charlie.Xia... .@gmail.comwrot e:
               But when I try to import test in python, it complains:
               import _test
               ImportError: ./_test.so undefined symbol: _Z9binary_opiiP FiiiE
              >
              The above is a mangled name so you've got some C vs C++ problems I'd
              say.
              >
              You could try putting some extern "C" {} in around all the functions
              which are imported and exported.  Have a look at the code SWIG
              generates and see if it puts some extern "C" in and match what it
              does in your code.
              >
              We used to use SWIG in for python embedding in our C++ project, but we
              found that using ctypes is a lot easier.  You just write C .so/.dll
              and use ctypes to access them.  You can do callbacks and embedding
              python like this too.
              >
              Thanks Nick.
              >
              I tried your method, if I am right(please see the attached details),
              and I still got the undefined symbol error like previous. The only
              difference is "_Z9binary_opii PFiiiE" changed to "binary_op" . Could you
              help me more on this. It seems to have a mixed problems here and I
              guess what you've pointed out is one of them. But really, what I do
              now is just try to reproduce the example, how can this fails? What my
              ultimate need is wrapping up a template function taking template
              function pointer as argument. Did you ever try that? Many thanks
              already anyway.
              ------error message----------
              Traceback (most recent call last):
                File "<stdin>", line 1, in <module>
                File "test.py", line 7, in <module>
                  import _test
              ImportError: ./_test.so: undefined symbol: binary_op
              ----------------------------------
              Hi Charlie,

              I think you're overcomplicatin g. Here's what I think what you want:
              (Unproduced.)
              >>binary_op( 3, 4, myadd )
              7
              >>binary_op( 3, 4, mysub )
              -1
              >>binary_op( 3, 4, mymul )
              12

              Correct?

                Comment

                • Nick Craig-Wood
                  #5
                  Re: C Function Pointer Wrapping Example not working

                  Charlie <Charlie.Xia.FD U@gmail.comwrot e:
                  >
                  ?But when I try to import test in python, it complains:
                  ?import _test
                  ?ImportError: ./_test.so undefined symbol: _Z9binary_opiiP FiiiE
                  The above is a mangled name so you've got some C vs C++ problems I'd
                  say.

                  You could try putting some extern "C" {} in around all the functions
                  which are imported and exported. ?Have a look at the code SWIG
                  generates and see if it puts some extern "C" in and match what it
                  does in your code.

                  We used to use SWIG in for python embedding in our C++ project, but we
                  found that using ctypes is a lot easier. ?You just write C .so/.dll
                  and use ctypes to access them. ?You can do callbacks and embedding
                  python like this too.
                  >
                  Thanks Nick.
                  >
                  I tried your method, if I am right(please see the attached details),
                  and I still got the undefined symbol error like previous. The only
                  difference is "_Z9binary_opii PFiiiE" changed to "binary_op" . Could you
                  help me more on this. It seems to have a mixed problems here and I
                  guess what you've pointed out is one of them. But really, what I do
                  now is just try to reproduce the example, how can this fails? What my
                  ultimate need is wrapping up a template function taking template
                  function pointer as argument. Did you ever try that? Many thanks
                  already anyway.
                  >
                  FILE and ERROR details:
                  >
                  %module test
                  %{
                  #include "test.h"
                  %}
                  %include "test.h"
                  >
                  %callback("%s_c b");
                  int myadd( int, int ); //myadd_cb
                  int mysub( int, int ); //mysub_cb
                  int mymul( int, int ); //mymul_cb
                  %nocallback;
                  >
                  extern "C"{
                  int binary_op(int a, int b, int (*op)(int,int) );
                  int myadd( int a, int b ) { return a+b; };
                  int mysub( int a, int b ) { return a-b; };
                  int mymul( int a, int b ) { return a*b; };
                  }
                  >
                  Traceback (most recent call last):
                  File "<stdin>", line 1, in <module>
                  File "test.py", line 7, in <module>
                  import _test
                  ImportError: ./_test.so: undefined symbol: binary_op
                  Nowhere in your code is the definition of binary_op - that is why you
                  get a linker error.

                  Is it defined in another C file? If so you need to link it with the
                  swig wrapper before you make the .so

                  --
                  Nick Craig-Wood <nick@craig-wood.com-- http://www.craig-wood.com/nick

                    Comment

                    • Charlie
                      #6
                      Re: C Function Pointer Wrapping Example not working

                      Nowhere in your code is the definition of binary_op - that is why you
                      get a linker error.
                      >
                      Is it defined in another C file?  If so you need to link it with the
                      swig wrapper before you make the .so
                      >
                      Thanks for pointing out. I sorted the code out finally!

                      Charlie

                        Comment

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