[Boost-users] how to pass pointer to boost.python function in python?

28 Aug 2006

      Dear all,

I wraped a v_varray class into python by boost.
I called it in python, most of its attributes work well. Only when I call
a.push(1.0),it crashed  due to  not match  type.The problem is that my input
argument in c++ is float*(for passing an array) while python has no pointer
type.

How can I pass a variable in python to a.push() to make sure it work
correctly?

Many thanks for help!

Javen

/*************************running result in python:****************/
...
...
...
a.push(1.0)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
Boost.Python.ArgumentError: Python argument types in
    array_floatstar.push(array_floatstar, float)
did not match C++ signature:
    push(v_array {lvalue}, float*)
/*************************v_array def in stack.h:****************/
#ifndef _STACK_H
#define _STACK_H
#include 

template<class T> class v_array{
 public:
  int index;
  int length;
  T* elements;

  T last() { return elements[index-1];}
  void decr() { index--;}
  v_array() { index = 0; length=0; elements = NULL;}
  T& operator[](unsigned int i) { return elements[i]; }

  void push(const T &new_ele)
  {
    while(index >= length)
    {
      length = 2*length + 3;
      elements = (T *)realloc(elements,sizeof(T) * length);
    }
    this->elements[index++] = new_ele;
  }
  void alloc(int newLength)
  {
    elements = (T *)realloc(elements, sizeof(T) * newLength);
    length = newLength;
  }

  T pop()
  {
    if (index > 0)
        return this->elements[--index];
    else
    return T();
  }

};
#endif

/*************************stack.cpp for boost.python(bjam need it to build a
stack.so file):****************/
// Boost Includes
==============================================================
#include 
#include 

// Includes
====================================================================
#include "stack.h"

// Using
=======================================================================
using namespace boost::python;

// Declarations
================================================================
BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(float)

// Module
======================================================================
BOOST_PYTHON_MODULE(stack)
{
    class_< v_array >("array_floatstar", init<  >())
        .def(init< const v_array& >())
        .def_readwrite("index", &v_array::index)
        .def_readwrite("length", &v_array::length)
        .def_readwrite("elements", &v_array::elements)
        .def("last", &v_array::last, return_value_policy<
return_opaque_pointer >())
        .def("decr", &v_array::decr)
        .def("push", &v_array::push)
        .def("alloc", &v_array::alloc)
        .def("pop", &v_array::pop, return_value_policy<
return_opaque_pointer >())
    ;

}

-- 
Qinfeng(Javen) Shi

Research School of Information Sciences and Engineering
Australian National University
Locked Bag 8001
Canberra ACT 2601