pasando C++ puntero doble a python

Question

Podría pasar una matriz de una dimensión a python como a continuación. y me pregunto si puedo pasar una matriz de doble puntero C++ a python usando ctypes, numpy.

test.cpp:

#include <stdio.h> 
extern "C" void cfun(const void * indatav, int rowcount, int colcount, void * outdatav); 

void cfun(const void * indatav, int rowcount, int colcount, void * outdatav) { 
    //void cfun(const double * indata, int rowcount, int colcount, double * outdata) { 
    const double * indata = (double *) indatav; 
    double * outdata = (double *) outdatav; 
    int i; 
    puts("Here we go!"); 
    for (i = 0; i < rowcount * colcount; ++i) { 
     outdata[i] = indata[i] * 4; 
    } 
    puts("Done!"); 
} 

test.py:

import numpy 
import ctypes 

indata = numpy.ones((5,6), dtype=numpy.double) 
outdata = numpy.zeros((5,6), dtype=numpy.double) 
lib = ctypes.cdll.LoadLibrary('./ctest.so') 
fun = lib.cfun 
# Here comes the fool part. 
#fun(ctypes.c_void_p(indata.ctypes.data), ctypes.c_void_p(outdata.ctypes.data)) 

fun(ctypes.c_void_p(indata.ctypes.data), ctypes.c_int(5), ctypes.c_int(6), 
    ctypes.c_void_p(outdata.ctypes.data)) 


print 'indata: %s' % indata 
print 'outdata: %s' % outdata 

Answer 1

Aquí está una manera. No vi una buena manera de usar numpy con doble **.

test.cpp (Windows)

#include <stdio.h> 

extern "C" __declspec(dllexport) void cfun(const double ** indata, int rowcount, int colcount, double ** outdata) { 
    for (int i = 0; i < rowcount; ++i) { 
     for (int j = 0; j < colcount; ++j) { 
      outdata[i][j] = indata[i][j] * 4; 
     } 
    } 
} 

test.py

import numpy 
import ctypes 

# Allocate array of double* 
indata = (ctypes.POINTER(ctypes.c_double) * 5)() 
for i in range(5): 
    # Allocate arrays of double 
    indata[i] = (ctypes.c_double * 6)() 
    for j in range(6): 
     indata[i][j] = 1.0 

outdata = (ctypes.POINTER(ctypes.c_double) * 5)() 
for i in range(5): 
    outdata[i] = (ctypes.c_double * 6)() 
    for j in range(6): 
     outdata[i][j] = 1.0 

lib = ctypes.cdll.LoadLibrary('test') 
fun = lib.cfun 

def dump(a,rows,cols): 
    for i in range(rows): 
     for j in range(cols): 
      print a[i][j], 
     print 

dump(indata,5,6) 
fun(ctypes.byref(indata),5,6,ctypes.byref(outdata)) 
dump(outdata,5,6) 

salida

1.0 1.0 1.0 1.0 1.0 1.0 
1.0 1.0 1.0 1.0 1.0 1.0 
1.0 1.0 1.0 1.0 1.0 1.0 
1.0 1.0 1.0 1.0 1.0 1.0 
1.0 1.0 1.0 1.0 1.0 1.0 
4.0 4.0 4.0 4.0 4.0 4.0 
4.0 4.0 4.0 4.0 4.0 4.0 
4.0 4.0 4.0 4.0 4.0 4.0 
4.0 4.0 4.0 4.0 4.0 4.0 
4.0 4.0 4.0 4.0 4.0 4.0