Boost.Python - error with parametrized constructor

Question

I have got a toy class from tutorialspoint in a file test.h:

class Box {
   public:

      Box(int l, int b, int h)
      {
        length = l;
        breadth = b;
        height = h;       
      }

      double getVolume(void) {
         return length * breadth * height;
      }
      void setLength( double len ) {
         length = len;
      }
      void setBreadth( double bre ) {
         breadth = bre;
      }
      void setHeight( double hei ) {
         height = hei;
      }

   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

In the another file I have:

BOOST_PYTHON_MODULE(test)
{
  namespace python = boost::python;

  python::class_<Box>("Box")
    .def("setLength",  &Box::setLength )
    .def("setBreadth", &Box::setBreadth)
    .def("setHeight",  &Box::setHeight )
    .def("getVolume",  &Box::getVolume );
}

When I compile this code I get the error message about the Box class constructor:

/usr/include/boost/python/object/value_holder.hpp:133:13: error: no matching function for call to ‘Box::Box()’
             BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_UNFORWARD_LOCAL, nil)
             ^

What am I missing?

Do I need to write the constructor paramaters in BOOST_PYTHON_MODULE()? If so, how to do it?

mohabouje · Accepted Answer · 2019-04-04 09:19:40Z

2

You dont have a default constructor and you are missing the one you declared:

BOOST_PYTHON_MODULE(test) {
  namespace python = boost::python;

  python::class_<Box>("Box", boost::python::init<int, int, int>())
    .def("setLength",  &Box::setLength )
    .def("setBreadth", &Box::setBreadth)
    .def("setHeight",  &Box::setHeight )
    .def("getVolume",  &Box::getVolume );
}

edited Apr 4, 2019 at 9:19

answered Apr 4, 2019 at 8:51

mohabouje

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4 Comments

mohabouje Over a year ago

I do not understand either @YSC, this fixes the problem.

Matthieu Brucher Over a year ago

Actually the answer, better than @YSC suggestion ( as it changes the contract of the object, sorry!).

PintoDoido Over a year ago

error: ‘init’ is not a member of ‘boost’ python::class_<Box>("Box", boost::init<int, int, int>())

mohabouje Over a year ago

Sorry, the init function is defined in the boost::python namespace. I just updated the answer. @PintoDoido

YSC · Accepted Answer · 2019-04-04 08:51:02Z

1

The compiler is complaining that Box doesn't provide a default constructor BOOST_PYTHON_MODULE needs:

no matching function for call to ‘Box::Box()

Simply define one:

class Box {
public:
    Box() = default;
// [...]
};

Additionnaly, you can checkout mohabouje's answer.

answered Apr 4, 2019 at 8:51

YSC

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