Passing an array from python to shared DLL, seeing access violation error

Question

The C function from DLL:

Multi(double Freq, double Power, int ports[], int Size)
Need to pass the 3rd parameter as an array from python

Tried the following different codes:

A:

import ctypes
pyarr = [2,3]
arr = (ctypes.c_int * len(pyarr))(*pyarr)

lp = CDLL(CDLL_file)
lp.Multi(c_double(Freq), c_double(Power), arr ,c_int(Size))`

This code shows an error ## exception :: access violation reading 0x00000000000

B:

retarr = (ctypes.c_int*2)()
retarr[0] =2
retarr[1] =3

lp = CDLL(CDLL_file)
lp.Multi(c_double(Freq), c_double(Power), retarr ,c_int(Size))`

This code shows an error

## exception :: access violation reading 0x00000000000

C: The same code using ctypes.byref also tried ......

My understanding is the function expects an array as argument , Tries passing an array as such as well address. Both cases , it didn't work Do anyone sees any mistake in my understanding or any other to work this out ??

What is Size set to?

cdarke
– cdarke

2016-07-19 12:57:59 +00:00
Commented Jul 19, 2016 at 12:57 — cdarke
– cdarke, Commented Jul 19, 2016 at 12:57

Mark Tolonen · Accepted Answer · 2016-07-27 17:52:26Z

1

Specify your argtypes. Given this test.dll source:

#include <stdio.h>

__declspec(dllexport) void Multi(double Freq, double Power, int ports[], int Size)
{
    int i;
    printf("%f %f\n",Freq,Power);
    for(i = 0; i < Size; ++i)
        printf("%d\n",ports[i]);
}

This works:

from ctypes import *
dll = CDLL('test')
Multi = dll.Multi
Multi.argtypes = (c_double,c_double,POINTER(c_int),c_int)
Multi.restype = None

ports = (c_int * 2)(100,200)
Multi(1.1,2.2,ports,len(ports))

Output:

1.100000 2.200000
100
200

answered Jul 27, 2016 at 17:52

Mark Tolonen

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