Using SWIG wrapped functions from Windows .dll

5
votes

I'm having a problem using functions from a .dll shared library that is exported with SWIG interface.

Version Info

Python: 2.6.4

Swig: 2.0.4

The big picture is: I have some code developed under Linux using C++ and wrapped using SWIG. I compiled the C++ source into a .so object under Linux and use the .so library in Python.

Now, I need to migrate all these functions to windows and the equivalent for .so in Windows is a .dll. So, I planned to compile all the C++ source codes into a .dll and access them through Python.

So the normal procedure would be: have the C++ source -> wrap them using SWIG -> compile into .dll -> access through Python.

There is a huge .cxx source file generated using SWIG which contains all the functions I developed. The task now is to compile this SWIG generated file into a .dll so that I can use all the functions later. However, the .cxx file uses some weird way of wrapping all my functions and I have no clue how to use them.

The functions are wrapped as follows. Ssay I have a C++ class called sdrts_reverse_burst_ff, after wrapping, the class becomes a function in the .cxx file and is defined like this:

SWIGINTERN PyObject *_wrap_sdrts_reverse_burst_ff_sptr___deref__(PyObject *SWIGUNUSEDPARM(self), PyObject *args) {

PyObject *resultobj = 0;

boost::shared_ptr< sdrts_reverse_burst_ff > *arg1 = (boost::shared_ptr< sdrts_reverse_burst_ff > *) 0 ;

  void *argp1 = 0 ;

  int res1 = 0 ;

  PyObject * obj0 = 0 ;

  sdrts_reverse_burst_ff *result = 0 ;



  if(!PyArg_UnpackTuple(args,(char *)"sdrts_reverse_burst_ff_sptr___deref__",1,1,&obj0)) SWIG_fail;

  res1 = SWIG_ConvertPtr(obj0, &argp1,SWIGTYPE_p_boost__shared_ptrT_sdrts_reverse_burst_ff_t, 0 |  0 );

  if (!SWIG_IsOK(res1)) {

    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "sdrts_reverse_burst_ff_sptr___deref__" "', argument " "1"" of type '" "boost::shared_ptr< sdrts_reverse_burst_ff > *""'"); 

  }

  arg1 = reinterpret_cast< boost::shared_ptr< sdrts_reverse_burst_ff > * >(argp1);

  result = (sdrts_reverse_burst_ff *)(arg1)->operator ->();

  resultobj = SWIG_NewPointerObj(SWIG_as_voidptr(result), SWIGTYPE_p_sdrts_reverse_burst_ff, 0 |  0 );

  return resultobj;

fail:

  return NULL;

}

That's not all: near the end of this .cxx file there is a huge array which contains all the class functions like this:

PyMethodDef SwigMethods[] = {

  { (char *)"sdrts_reverse_burst_ff_sptr___deref__", _wrap_sdrts_reverse_burst_ff_sptr___deref__, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr___deref__(sdrts_reverse_burst_ff_sptr self)"},

  { (char *)"delete_sdrts_reverse_burst_ff_sptr", _wrap_delete_sdrts_reverse_burst_ff_sptr, METH_VARARGS, (char *)"delete_sdrts_reverse_burst_ff_sptr(sdrts_reverse_burst_ff_sptr self)"},

  { (char *)"sdrts_reverse_burst_ff_sptr_set_reverse_burst", _wrap_sdrts_reverse_burst_ff_sptr_set_reverse_burst, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_set_reverse_burst(sdrts_reverse_burst_ff_sptr self, int samples) -> int"},

  { (char *)"sdrts_reverse_burst_ff_sptr_enable_reverse_burst", _wrap_sdrts_reverse_burst_ff_sptr_enable_reverse_burst, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_enable_reverse_burst(sdrts_reverse_burst_ff_sptr self) -> int"},

  { (char *)"sdrts_reverse_burst_ff_sptr_reset", _wrap_sdrts_reverse_burst_ff_sptr_reset, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_reset(sdrts_reverse_burst_ff_sptr self) -> int"},

  { (char *)"sdrts_reverse_burst_ff_sptr_history", _wrap_sdrts_reverse_burst_ff_sptr_history, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_history(sdrts_reverse_burst_ff_sptr self) -> unsigned int"},

  { (char *)"sdrts_reverse_burst_ff_sptr_output_multiple", _wrap_sdrts_reverse_burst_ff_sptr_output_multiple, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_output_multiple(sdrts_reverse_burst_ff_sptr self) -> int"},

  { (char *)"sdrts_reverse_burst_ff_sptr_relative_rate", _wrap_sdrts_reverse_burst_ff_sptr_relative_rate, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_relative_rate(sdrts_reverse_burst_ff_sptr self) -> double"},

  { (char *)"sdrts_reverse_burst_ff_sptr_start", _wrap_sdrts_reverse_burst_ff_sptr_start, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_start(sdrts_reverse_burst_ff_sptr self) -> bool"},

  { (char *)"sdrts_reverse_burst_ff_sptr_stop", _wrap_sdrts_reverse_burst_ff_sptr_stop, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_stop(sdrts_reverse_burst_ff_sptr self) -> bool"},

  { (char *)"sdrts_reverse_burst_ff_sptr_nitems_read", _wrap_sdrts_reverse_burst_ff_sptr_nitems_read, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_nitems_read(sdrts_reverse_burst_ff_sptr self, unsigned int which_input) -> uint64_t"},

  { (char *)"sdrts_reverse_burst_ff_sptr_nitems_written", _wrap_sdrts_reverse_burst_ff_sptr_nitems_written, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_nitems_written(sdrts_reverse_burst_ff_sptr self, unsigned int which_output) -> uint64_t"},

  { (char *)"sdrts_reverse_burst_ff_sptr_detail", _wrap_sdrts_reverse_burst_ff_sptr_detail, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_detail(sdrts_reverse_burst_ff_sptr self) -> gr_block_detail_sptr"},

  { (char *)"sdrts_reverse_burst_ff_sptr_set_detail", _wrap_sdrts_reverse_burst_ff_sptr_set_detail, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_set_detail(sdrts_reverse_burst_ff_sptr self, gr_block_detail_sptr detail)"},

  { (char *)"sdrts_reverse_burst_ff_sptr_name", _wrap_sdrts_reverse_burst_ff_sptr_name, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_name(sdrts_reverse_burst_ff_sptr self) -> string"},

  { (char *)"sdrts_reverse_burst_ff_sptr_input_signature", _wrap_sdrts_reverse_burst_ff_sptr_input_signature, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_input_signature(sdrts_reverse_burst_ff_sptr self) -> gr_io_signature_sptr"},

  { (char *)"sdrts_reverse_burst_ff_sptr_output_signature", _wrap_sdrts_reverse_burst_ff_sptr_output_signature, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_output_signature(sdrts_reverse_burst_ff_sptr self) -> gr_io_signature_sptr"},

  { (char *)"sdrts_reverse_burst_ff_sptr_unique_id", _wrap_sdrts_reverse_burst_ff_sptr_unique_id, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_unique_id(sdrts_reverse_burst_ff_sptr self) -> long"},

  { (char *)"sdrts_reverse_burst_ff_sptr_to_basic_block", _wrap_sdrts_reverse_burst_ff_sptr_to_basic_block, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_to_basic_block(sdrts_reverse_burst_ff_sptr self) -> gr_basic_block_sptr"},

  { (char *)"sdrts_reverse_burst_ff_sptr_check_topology", _wrap_sdrts_reverse_burst_ff_sptr_check_topology, METH_VARARGS, (char *)"sdrts_reverse_burst_ff_sptr_check_topology(sdrts_reverse_burst_ff_sptr self, int ninputs, int noutputs) -> bool"},

  { (char *)"sdrts_reverse_burst_ff_sptr_swigregister", sdrts_reverse_burst_ff_sptr_swigregister, METH_VARARGS, NULL},

  { (char *)"reverse_burst_ff", _wrap_reverse_burst_ff, METH_VARARGS, (char *)"reverse_burst_ff(int max_samples) -> sdrts_reverse_burst_ff_sptr"},

  { NULL, NULL, 0, NULL }

};

I followed my old experience with .dlls and exported all the functions with a simple __declspec(dllexport) head. In Python, I can also call the _wrap_sdrts_reverse_burst_ff_sptr___deref__ I exported:

import ctypes

_dll_func_list = ctypes.WinDLL("func.dll")

_reverse_burst_ref = _dll_func_list._wrap_sdrts_reverse_burst_ff_sptr___deref__

Yet, that's the furthest I can approach. When I try to access the sub functions in that class, for example,

_class_ref._wrap_sdrts_reverse_burst_ff_sptr_set_reverse_burst(0)

the damned machine told me:

'_wrap_sdrts_reverse_burst_ff_sptr_set_reverse_burst' cannot be found.

When I try to call the function directly and pass in a parameter like this:

_dll_func_list ._wrap_sdrts_reverse_burst_ff_sptr_set_reverse_burst(0)

The machine says

WindowsError: exception: access violation reading 0x00000004

Does anyone know how to access exported SWIG wrapped functions using Python?

2
c++pythondllshared-librariesswig

2 Answers

2
votes

SWIG also generates a .py file, in addition to the .cxx file. Once you've built a DLL (or shared object) on your platform all you need to do to use that in Python itself is 

import ModuleName

where ModuleName is what you told SWIG to call the module, either via %module in the .i file for from the command line when you called it.

In the SWIG generated Python there is code to handle the loading of the DLL for you - no need to be using ctypes or anything like that with it. The generated code matches the interface you asked SWIG to wrap as closely as possible in Python and magically hands the calls off to the C++ side for you.

Thus if sdrts_reverse_burst_ff is a free function you can do:

import ModuleName

ModuleName.sdrts_reverse_burst_ff()

You need to make sure you build the DLL with the name SWIG expects it to have - it'll be pretty obvious from the exception that Python raises if that's not the case. You probably also want to link it against your implementation that contains sdrts_reverse_burst_ff() unless that's a header only function.

2
votes

So the final short answer appears to be that the C++ build should produce _my_dll.pyd (not _my_dll.dll) in order to be able to import my_dll in Python on Windows. This is in contrast to the Linux build, where one would build _my_dll.so

Simply renaming .dll file to .pyd works, but it is better to build it, as pointed out in comments above.