passant un double pointeur C++ vers python

Question

Je pourrais passer un tableau à une dimension à python comme ci-dessous. et je me demande si je peux passer tableau double pointeur c + + à python en utilisant 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

est ici un moyen. Je n'ai pas vu une bonne façon d'utiliser numpy avec double **.

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) 

Sortie

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