sample code for get and return numpy in C++

numpy_Capi

// From http://stackoverflow.com/questions/9128519/reading-many-values-from-numpy-c-api
/*
Make

g++ -o matrix_multiply.o -c matrix_multiply.cpp  -I{python include file  for numpy/noprefix.h} -I{python include}  -fPIC -O2 -Wno-deprecated -Wno-write-strings
g++ -o matrix_multiply.so -shared matrix_multiply.o -L{boost lib path} -lz -lm -ldl -lpthread -boost_python

Python code:
import numpy
import matrix_multiply
a = numpy.arange(1.0, 13.0,1.0)
b = a.reshape(3,4)
x = matrix_multiply.multiply( b, 4.0)
*/
#include <boost/python.hpp>

#include <exception>

#include <numpy/arrayobject.h>

using namespace boost::python;

struct WrongSizeError : public std::exception {
  const char* what() const throw() { return "Unsupported array size."; }
};

struct WrongTypeError : public std::exception {
  const char* what() const throw() { return "Unsupported array type."; }
};

// Boost::Python needs the translators
void translate_sz(const WrongSizeError& e)
{
  PyErr_SetString(PyExc_RuntimeError, e.what());
}

void translate_ty(const WrongTypeError& e)
{
  PyErr_SetString(PyExc_RuntimeError, e.what());
}

// multiply matrix of double (m) by f
object multiply(numeric::array m, double f)
{
  PyObject* m_obj = PyArray_FROM_OTF(m.ptr(), NPY_DOUBLE, NPY_IN_ARRAY);
  if (!m_obj)
    throw WrongTypeError();

  // to avoid memory leaks, let a Boost::Python object manage the array
  object temp(handle<>(m_obj));

  // check that m is a matrix of doubles
  int k = PyArray_NDIM(m_obj);
  if (k != 2)
    throw WrongSizeError();

  // get direct access to the array data
  const double* data = static_cast<const double*>(PyArray_DATA(m_obj));

  // make the output array, and get access to its data
  PyObject* res = PyArray_SimpleNew(2, PyArray_DIMS(m_obj), NPY_DOUBLE);
  double* res_data = static_cast<double*>(PyArray_DATA(res));

  const unsigned size = PyArray_SIZE(m_obj); // number of elements in array
  for (unsigned i = 0; i < size; ++i)
    res_data[i] = f*data[i];

  return object(handle<>(res)); // go back to using Boost::Python constructs
}

BOOST_PYTHON_MODULE(test)
{
  // register exception translators
  register_exception_translator<WrongSizeError>(&translate_sz);
  register_exception_translator<WrongTypeError>(&translate_ty);

  // tell Boost::Python under what name the array is known
  numeric::array::set_module_and_type("numpy", "ndarray");
  def("multiply", multiply);

  // initialize the Numpy C API
  import_array();
}