Wrapping a C++ class in Python using SWIG

问题

example.h:

#ifndef EXAMPLE_H
#define EXAMPLE_H

class Math {
 public:
    int pi() const;
    void pi(int pi);
 private:
    int _pi;
};

#endif

example.cpp:

#include "example.h"

int Math::pi() const {
    return this->_pi;
}  
void Math::pi(int pi) {
    this->_pi = pi;
}

example.swig:

%module example
%{ 
    #define SWIG_FILE_WITH_INIT
    #include "example.h"
%}
%include "example.h"

I then generate the wrappers, "example.py" and "example_wrap.c" using:

swig  -python example.swig

When I try to compile the wrapper class using:

g++ -fPIC -c example.cpp example_wrap.c -I/usr/local/include/python2.6/

I get the following error:

example_wrap.cpp: In function "PyObject* Swig_var_Math_get()":
example_wrap.cpp:2725: error: expected primary-expression before "void"
example_wrap.cpp:2725: error: expected ")" before "void"

The Error is at the following line :

pyobj = SWIG_NewPointerObj(SWIG_as_voidptr(&Math), SWIGTYPE_p_class,  0 );

#define SWIG_as_voidptr(a) (void *)((const void *)(a))

Is it the right way to generate the wrapper class "example_wrap.c"?

回答1:

I think the swig command should be "swig -c++ -python example.swig"

回答2:

There's not enough information here to be sure what's wrong, but I have two ideas for things you can try.

Your g++ invocation is compiling a C source file as if it were C++. This is not guaranteed to work. Try instead

gcc -I/usr/local/include/python2.6 -fPIC -c example_wrap.c
gcc -I/usr/local/include/python2.6 -fPIC -c example.cpp
g++ -shared example_wrap.o example.o -o example.so

(yes, srsly, only use g++ for the link)

If that doesn't work, compile example_wrap.c like this:

gcc -I/usr/local/include/python2.6 -fPIC -c -save-temps example_wrap.c

That will fail the same way but will produce a file named example_wrap.i which is the result of preprocesing. It will be gigantic. Search that file for the function Swig_var_Math_get, and add to your question the complete text of that function (but nothing else).

回答3:

Thanks for your replay!

The -C++ option generated the C++ class for the wrapper. swig -c++ -v -python example.swig

I used g++ to compile the wrapper.

g++ -fPIC -c example.cpp example_wrap.cxx -I/usr/local/include/python2.6/

And the following command to buikd the shared object. Ofcourse, we need to remove the superflous includes (-I) and libraries (-L). The important flags are '-shared' and '-fPIC'.

g++ example_wrap.o example.o -L/u01/app/oracle/product/1020.full/lib  -I/usr/local/ssl/include  -L/usr/local/ssl/lib -lclntsh -lssl -lcrypto -ldl -L/usr/local/lib -L/lib64 -L/usr/local/lib/python2.6/ -lboost_system -lboost_filesystem -lboost_thread -lboost_date_time -lglog -lmodpbase64 -lpthread -ldl -lrt -shared -fPIC -o _example.so

来源：https://stackoverflow.com/questions/4596484/wrapping-a-c-class-in-python-using-swig

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