Question

I have C++ class and need to use it in python code. For that, using SWIG to generate a wrapper class. As per the documentation configured the example.i

/* File: example.i */
%module example

%{
#define SWIG_FILE_WITH_INIT
#include "item.h"
#include "GradedComplex.h"
#include "GradedDouble.h"
%}

%include "item.h"
%include "GradedComplex.h"
%include "GradedDouble.h"

And tried to build it using following command

c:>swig -c++ -python example.i

c:>python setup.py build_ext --inplace

The item.h is :

#ifndef __ITEM_H__
#define __ITEM_H__

#include <complex>
#include <functional>
#include <string>

template<typename T>
class Item
{
  std::string name_;
  T val_;

public:
  Item(std::string name, T val) : name_(name), val_(val) {}
  Item(Item<T> &rhs) : name_(rhs.name_), val_(rhs.val_) {}
  Item(const Item<T> &rhs) : name_(rhs.name_), val_(rhs.val_) {}
  ~Item() {}

  std::string name() const { return name_; }
  T operator()() const { return val_; }
  double norm() const { return sqrt(val_ * val_); }
  Item<T> &operator+=(Item<T> &rhs)
  {
    val_ += rhs();
    return *this;
  }
  Item<T> &operator-=(Item<T> &rhs)
  {
    val_ -= rhs();
    return *this;
  }
  Item<T> &operator*=(Item<T> &rhs)
  {
    val_ *= rhs();
    return *this;
  }
};

template<>
class Item<std::complex<double> >
{
  std::string name_;
  std::complex<double> val_;

public:
  Item(std::string name, std::complex<double> val) : name_(name), val_(val) {}
  Item(Item<std::complex<double> > &rhs) : name_(rhs.name_), val_(rhs.val_) {}
  Item(const Item<std::complex<double> > &rhs) : name_(rhs.name_), val_(rhs.val_) {}
  ~Item() {}

  std::string name() const { return name_; }
  std::complex<double> operator()() const { return val_; }
  double norm() const { return sqrt(val_.real() * val_.real() + val_.imag() * val_.imag()); }
};

template<typename T>
struct ItemComparator : public std::binary_function<Item<T>, Item<T>, bool>
{
  inline bool operator()(Item<T> lhs, Item<T> rhs)
  {
    return lhs.norm() < rhs.norm();
  }
};

#endif

But still I am getting the following error

example_wrap.cxx(3275) : error C2512: 'Item<std::complex<double>>' : no appropriate default constructor available

c:\documents and settings\swig\Item.h(38) : warning C45
21: 'Item<T>' : multiple copy constructors specified
        with
        [
            T=double
        ]
        example_wrap.cxx(3425) : see reference to class template instantiation '
Item<T>' being compiled
        with
        [
            T=double
        ]
error: command '"C:\Program Files\Microsoft Visual Studio 9.0\VC\BIN\cl.exe"' fa
iled with exit status 2

Please give me some suggestion.

Answer 1

Use this option for building extension…
swig -nodefaultctor example.i