How To Pass Python List Address

I want to convert c++ code to python. I have created a python module using SWIG to access c++ classes. Now I want to pass the following c++ code to Python C++ #define LEVEL 3 dou

Solution 1:

Using raw double * and length as an interface is more difficult in SWIG. You'd need to write a typemap for the parameter pair that can intelligently read the array given the size. Easier to use SWIG's built-in vector support.

Example, with display support:

GradedDouble.i

%module GradedDouble

%{
#include "GradedDouble.h"
%}

%include <std_vector.i>
%include <std_string.i>
%template(DoubleVector) std::vector<double>;
%rename(__repr__) ToString;
%include "GradedDouble.h"

GradedDouble.h

#include <vector>
#include <string>
#include <sstream>

class GradedDouble
{
    std::vector<double> thre_;
public:
    GradedDouble(const std::vector<double>& dbls) : thre_(dbls) {}
    ~GradedDouble() {}
    std::string ToString() const
    {
        std::ostringstream ss;
        ss << "GradedDouble(";
        for(auto d : thre_)
            ss << ' ' << d;
        ss << " )";
        return ss.str();
    }
};

Output

>>> import GradedDouble as gd
>>> x=gd.GradedDouble([1.2,3.4,5.6])
>>> x
GradedDouble( 1.2 3.4 5.6 )

Solution 2:

Another method for doing this is by using SWIG cpointer and carrays. Sample code is below:

Interface file:

%module example
%include "cpointer.i"
%{
#include "Item.h"
#include "GradedDouble.h"
extern void avg(double *buf);
%}
%pointer_class(double, doublep);

%include "carrays.i"
%array_class(double, doubleArray);
%include <std_string.i>
%include "Item.h"
%include "GradedDouble.h"
%template(Double) Item<double>;

Python code:

LEVEL = 3
thre = [1, 100, 10000]
a = example.doubleArray(LEVEL)
for i in xrange(LEVEL):
    a[i] = thre[i]

gd=example.GradedDouble(LEVEL,a)

result = example.doublep()
gd.avg(result)
print result.value()

This worked for me